Grand Terrace City Council
February 10, 2026

• Participation in LHMP Planning Team meetings
• Collection of valuable local information and other requested data • Decision on plan process and content
• Development and prioritization of mitigation actions for the LHMP • Review and comment on plan drafts
• Coordination and involvement in the public engagement process Table 2-3, LHMP Planning Team, identifies both LHMP Project Management Team and LHMP Planning Team members, along with their roles in plan development.

Table 2-3
LHMP Planning Team
Name Title/Role Organization LHMP Planning Team
Role
LHMP Project Management Team
Scott Hutter
Planning &
Development Services
Director/Project
Manager
City of Grand Terrace
City Project Manager –
Organization of LHMP
Planning Team and
meetings, development
of and participation in
community outreach,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion, draft LHMP
review/comment.

Gabriel Arguelles Assistant Planner City of Grand Terrace Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion, draft LHMP
review/comment.

Shanita Tillman Senior Management
Analyst City of Grand Terrace
Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion

Name Title/Role Organization LHMP Planning Team
Role
Konrad Bolowich City Manager City of Grand Terrace
Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
Judith Garcia Public Works
Department City of Grand Terrace
Project goals and
objectives identification,
hazard identification
and prioritization
LHMP Planning Team
Michelle DeGrandeFuentesSenior Management
Analyst City of Grand Terrace
Project goals and
objectives identification,
hazard identification
and prioritization
Luis Gardea Building Official City of Grand Terrace
Critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
Bill Hussey Mayor City of Grand Terrace
Project goals and
objectives identification,
hazard identification
and prioritization
Doug Wilson Mayor Pro Tempore City of Grand Terrace
Critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
Michelle Sabino Council Member City of Grand Terrace
Project goals and
objectives identification,
hazard identification
and prioritization
Jeff Allen Council Member City of Grand Terrace
Critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
Kenneth J.

Henderson Council Member City of Grand Terrace
Critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion

Name Title/Role Organization LHMP Planning Team
Role
Isaias Hernandez Disaster Program
Manager
American Red Cross -
Southern California
Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
Tom Ingalls
Fire Marshal /
Emergency
Preparedness
City of Loma Linda
Project goals and
objectives identification,
hazard identification
and prioritization
Mario Suarez Planning Manager City of Colton
Project goals and
objectives identification,
hazard identification
and prioritization
Lieutenant Michele
Mahan
Emergency Operations
Manager
City of San Bernardino
Police Dept.

Project goals and
objectives identification,
hazard identification
and prioritization
Mark D. Annas Emergency Services
Administrator City of Riverside
Project goals and
objectives identification,
hazard identification
and prioritization
Anunciata Greer Homeland Security
Planner (UASI) City of Riverside
Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
David Bell
Director of
Maintenance &
Operations
Colton Joint Unified
School District
Project goals and
objectives identification,
hazard identification
and prioritization
Anthony Ortiz
Assistant
Superintendent of
Student Services
Colton Joint Unified
School District
Project goals and
objectives identification,
hazard identification
and prioritization
Patrick Keith Environmental Health &
Safety Administrator
San Bernardino
Community College
District
Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion

Name Title/Role Organization LHMP Planning Team
Role
Gary Jaeger Assistant Chief San Bernardino County
Fire
Project goals and
objectives identification,
hazard identification
and prioritization
Don Hough General Manager Riverside Highland
Water Company
Project goals and
objectives identification,
hazard identification
and prioritization,
critical facilities review,
risk assessment/
vulnerability discussion,
mitigation action
discussion
Matt Brown Vice President Grand Terrace Area
Chamber of Commerce
Project goals and
objectives identification,
hazard identification
and prioritization
A series of LHMP Planning Team meetings and smaller focus group meetings were hosted during the LHMP update process. The LHMP Planning Team Meeting was hosted during January 2025 to introduce the LHMP, outline the planning process, and discuss priority natural hazards for the plan. Stakeholders on the LHMP Planning Team were then invited to participate in focus group meetings, hosted during February and March 2025. Focus groups were either held with a single stakeholder or a group of stakeholders with similar responsibilities or interests. The meeting series was concluded with Focus Group Meeting #4, hosted on March 12, 2025. The meeting series is summarized below in Table 2-4, LHMP Planning Team and Focus Group Meeting Summary.

Meetings were held virtually via Microsoft Teams, to accommodate stakeholders near the City, distributed throughout the region, and remote staff serving on the LHMP Consultant team. Meeting materials, including PowerPoint presentations, sign-in sheets, agendas, notes, and other relevant handouts, are provided in Appendix B, LHMP Planning Team Documentation.

The draft LHMP was electronically circulated to the LHMP Planning Team on April 15, 2025, for an internal review period concluding on July 15, 2025. At the conclusion of the internal review period, minor comments, edits, and points of clarification were requested in the LHMP.

Documentation of this process is included in Appendix B, LHMP Planning Team Documentation.

Table 2-4
LHMP Planning Team and Focus Group Meeting Summary
Date/Time Meeting Attendees Discussion Items
July 31, 2024
10:30 AM – 11:30 PM LHMP Kickoff Meeting LHMP Planning Team (all)
• Project Background
• Purpose &
Requirements of the
LHMP
• Project Goals,
Objectives and
Expectations
• Hazard Identification
and Prioritization
January 29, 2025
3:00 PM – 4:00 PM
LHMP Planning Team
Stakeholder Meeting
LHMP Planning Team
(all)
• Critical Facilities
Review
• Risk/Vulnerability
Discussion
• Mitigation Action
Discussion
February 25, 2025
3:30 PM – 4:30 PM
Focus Group Meeting
#1
• LHMP Project
Management Team
• Internal City Staff
• Critical Facilities
Review
• Risk/Vulnerability
Discussion
• Mitigation Action
Discussion
February 27, 2025
3:30 PM – 4:30 PM
Focus Group Meeting
#2
• LHMP Project
Management Team
• Representatives
from Neighboring
Communities,
Emergency
Management,
Utilities
• Critical Facilities
Review
• Risk/Vulnerability
Discussion
• Mitigation Action
Discussion
March 4, 2025
4:30 PM – 5:30 PM
Focus Group Meeting
#3
• LHMP Project
Management Team
• Representatives
from CommunityBased
Organizations,
School Districts,
and Higher
Education
• Critical Facilities
Review
• Risk/Vulnerability
Discussion
• Mitigation Action
Discussion
March 12, 2025
11:00 AM – 11:30 AM
Focus Group Meeting
#4
• LHMP Project
Management Team
• City Public Works
Department
• Critical Facilities
Review
• Risk/Vulnerability
Discussion
• Mitigation Action
Discussion

A public outreach and engagement strategy was developed to maximize public involvement in the LHMP planning process. The LHMP public outreach strategy included a dedicated webpage, a community survey, a community outreach event, and public review draft distribution, as described below; refer to Appendix B, LHMP Planning Team Documentation. The LHMP public outreach process was specifically designed to maximize participation and input from all community members, including underserved groups and vulnerable populations.

Webpage
A dedicated webpage was developed on the City’s website for the LHMP planning process. The webpage provided information on the LHMP, and how the public can get involved in the planning process. Contact information was included for comments or questions via email. A link to complete the community survey was posted to encourage participation. The website was updated throughout the planning process and provided notifications and access to LHMP materials. The draft LHMP was also made available for public review on this webpage, available here: Planning & Development Services - City of Grand Terrace.

Virtual outreach on the City’s website posted for the entirety of the LHMP development process allowed for maximum audience reach, including underserved and vulnerable populations.

Traditionally, virtual outreach has the ability to reach community members who may be unable to attend in-person meetings or hearings. Individuals can access all information at their own convenience and have the ability to communicate directly with City staff regarding questions or comments.

Community Survey
A community survey was developed to obtain input from the community about various hazard mitigation topics. In addition to basic demographic information (e.g., zip code and age), the survey asked residents to identify specific safety concerns, including identifying what hazards they felt were most likely to impact their neighborhood or property. Participants were also asked what actions they had taken to be more resistant to hazards, and preferences for future communication methods from the City. A survey link was posted on the LHMP webpage and a QR code was distributed on a printed handout at the Light Up Grand Terrace event. Members of the LHMP Planning Team also distributed the survey link to colleagues and constituents within their jurisdiction.

The survey was opened on November 19, 2024, and closed on March 11, 2025. A total of 45 responses were received. Of the 45 participants, approximately 58 percent provided contact information and requested notification when the draft LHMP becomes available for public review.

Input received was generally similar with feedback from the Light Up Grand Terrace pop-up event as outlined below. Survey input directly influenced the final hazard rankings, provided in Section

4.0, Hazard Assessment. Further details received allow the City to better target future outreach and engagement activities regarding the LHMP. The survey specifically provides outreach with underserved and vulnerable populations who may not have the capacity or ability to attend inperson outreach events or hearings. A detailed community outreach summary is included in Appendix B, LHMP Planning Team Documentation.

Pop-Up Community Outreach
The City of Grand Terrace hosted an interactive popup booth focused on LHMP outreach and content from during December 2024. The free event called
the “Light Up Grand Terrace Tree Lighting Event”
was held on December 5, 2024, from 4:00 PM to
8:00 PM. The intent of this outreach event was to
use the “Whole Community” approach and meet
stakeholders/constituents at a convenient location
during a regularly scheduled and free event.

The LHMP Consultant, Michael Baker International,
set up several informational boards regarding the
LHMP update process and information about key
community lifelines. Participants were given sheets
of five dot stickers to place on the list of Grand
Terrace hazards indicating which of the hazards
were a top concern or priority. Results from these
outreach events, along with the board illustrations
are documented in Appendix B, LHMP Planning
Team Documentation. Feedback was generally
consistent with the results from the community survey exercise, with the top hazard of concern remaining the same amongst all pop-up events. City staff was available to answer questions from the public regarding hazard mitigation and resilience related to the City. Approximately 30-50 participants took part in the natural hazard ranking activity during the pop-up events.

In addition to the activities and informational boards, staff passed out an informational postcard describing the LHMP Update process containing the Community Survey QR Code to provide them the opportunity to give additional input. Photos from the event are included as Figure 2-1, Pictures from the Light Up Grand Terrace Pop-Up Event, and an illustration of this handout is included below as Figure 2-2, Postcard Handout from Grand Terrace Outreach Event.

Definitions:

Whole Community: engaging the full
capacity of private and nonprofit sectors,
including businesses, faith-based and
disability organizations, and the general
public, in conjunction with the
participation of local, tribal, state, and
Federal governmental partners (FEMA)
Social Vulnerability: characteristics of a
person or group that affect their capacity
to anticipate, cope with, resist, and
recover from the impact of a discrete
and identifiable disaster in nature or
society.

Figure 2-1
Pictures from the Light Up Grand Terrace Pop-Up Event Figure LHMP Outreach
Light Up Grand Terrace
Christmas Tree Lighting
December 5, 2024

Figure 2-2
Postcard Handout from Grand Terrace Outreach Events
Public Review Draft LHMP
A draft of the LHMP was made available on the LHMP webpage for the public to review and comment for a two-week period beginning September 24, 2025 and ending on October 8, 2025.

Notification of the draft LHMP availability for review and comment was distributed via the City’s website and hard copies were made available at the City Clerk’s Office, City Hall, and the Grand Terrace Public Library. The LHMP received no comments on the draft LHMP. Documentation of this process is included in Appendix B, LHMP Planning Team Documentation.

The LHMP Planning Team referenced a variety of plans, studies, data, and technical reports available from local, State, and federal sources to prepare the LHMP update. Primary sources were reviewed and incorporated as part of the LHMP planning process, and are listed in Table 2- 5, Existing Plans, Studies, Reports, and Other Technical Data/Information. A complete list of references is included in Section 7.0, References.

Table 2-5
Existing Plans, Studies, Reports, and Other Technical Data/Information Existing Plans, Studies, Reports, Planning Process /
Area of Document Inclusion
FEMA Local Mitigation Planning Policy Guide
(2025)
Multiple Plan Sections; Planning Process, Plan
Maintenance
FEMA Local Mitigation Planning Handbook Multiple Plan Sections; Planning Process, Plan Maintenance
California State Hazard Mitigation Plan (2023) Multiple Plan Sections; Hazard Profiles San Bernardino County Multi-Jurisdictional
Hazard Mitigation Plan (2022)
Multiple Plan Sections; Hazard Profiles
San Bernardino County Emergency
Operations Plan (2019)
Multiple Plan Sections; Hazard Profiles, Mitigation
Strategy
2010 City of Grand Terrace General Plan Multiple Plan Sections; Mitigation Strategy 2018 Grand Terrace Active Transportation
Plan Multiple Plan Elements
2018 City of Grand Terrace Local Hazard
Mitigation Plan Hazard Profiles
2019 San Bernardino County Emergency
Operations Plan Hazard Profiles
2020 Barton Road Specific Plan Multiple Plan Sections
2020 Integrated Regional Urban Water
Management Plan (IRUWMP) Multiple Plan Sections
Housing Element (2021 – 2029) Multiple Plan Sections
In accordance with FEMA requirements, the LHMP Planning Team identified and prioritized the hazards affecting the City and assessed vulnerability from those hazards. Results from this phase of the LHMP planning process aided subsequent identification of appropriate mitigation actions to reduce risk from these hazards; refer to Section 5.0, Mitigation Strategy.

Based on a review of past hazards, as well as a review of existing plans, reports, and other technical studies, data, and information, the LHMP Planning Team determined which specific hazards could affect the City. Content for each hazard profile is provided in Section 4.0, Hazard Assessment.

Hazard profiling exposes the unique characteristics of individual hazards and begins the process of determining which areas within the City are vulnerable to specific hazards. The vulnerability assessment included input from the LHMP Planning Team and a GIS overlaying method to map hazard risk assessments. Using these methodologies, critical facilities impacted by hazards were identified and potential loss estimates were determined, where available. Detailed information on the vulnerability assessments for each hazard is provided in Section 4.0, Hazard Assessment.

The LHMP Planning Team reviewed mitigation goals from the previous 2017 LHMP and made minor editorial edits for clarification. Hazard mitigation goals were discussed during Meeting #1, before finalization and incorporation into the LHMP. The Mitigation Goals are included in Section

1.0, Introduction.

A capabilities assessment is a comprehensive review of all mitigation capabilities and tools currently available to the City for mitigation action implementation, as prescribed in the LHMP.

The LHMP Planning Team identified the planning and regulatory; administrative and technical; financial; and education and outreach capabilities to implement mitigation actions, as detailed in Section 5.0, Mitigation Strategy.

As part of the LHMP planning process, the LHMP Planning Team worked to identify and develop mitigation actions, after which mitigation actions were prioritized as high, medium, or low. A detailed discussion of the identification and prioritization of mitigation actions, and the creation of the implementation strategy is provided in Section 5.0, Mitigation Strategy.

This plan will be submitted to Cal OES and FEMA for review. Upon receiving “approvable pending adoption” notification from FEMA, this plan will be presented to the City for consideration and approval by the Grand Terrace City Council. If approved, a copy of the resolution will be provided in Appendix A, City of Grand Terrace LHMP Adoption Resolution.

Plan maintenance procedures, found in Section 6.0, Plan Maintenance and Capabilities, include the measures the City will take to ensure the LHMP’s continuous long-term implementation. The procedures also include the manner in which the LHMP will be regularly monitored, reported upon, evaluated, and updated to remain a current and meaningful planning document.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-1
SECTION 3: COMMUNITY PROFILE

3.1 Physical Setting
The City of Grand Terrace is located within western San Bernardino County, about 60 miles east of the Pacific Ocean and in the foothills of the Blue Mountain to the east and the La Loma Hills to the west. The City is comprised of roughly 2,240 acres (3.5 square miles). The Interstate 215 traverses the western portion of the City. The City of Grand Terrace is bordered by the City of Colton and the City of Loma Linda in San Bernardino County and by the City of Riverside, the City of Highgrove, and unincorporated areas of Riverside County.

3.2 History
The Tongva, also known as Gabrielino, Cahuilla, and Luiseno were the original inhabitants of the area of the City of Grand Terrace, however, many people still thrive today.1 The people of City of Grand Terrace was home to Native American communities for thousands of years.

In 1850, Mormon settlers arrived in San Bernardino Valley. In 1877, the Colton Land and Water Company, which later became the Colton-Terrace Water Company, organized bringing water from the artesian wells. With the construction of the Gage Canal in 1896, the area transformed into a thriving agricultural community known for its citrus groves.2 Originally the area was referred to as the Terrace, however in 1898, the name Grand was added to Terrace to refer to the area when the Riverside Highland Water Company started developing the area.3 The area experienced continued growth and development during the Southern California suburbia and sunbelt periods.

In 1904, Charles Patton and M. L. Howell purchased 300 acres and organized land in sections of 8 to 20 acres, naming their tract Grand Terrace. With a strong community push for cityhood, San Bernardino County incorporated the City of Grand Terrace on November 30, 1978, with Tony Petta as the first mayor.

3.3 Demographics
Basic demographic and socioeconomic data for the City of Grand Terrace (population, education, employment, and housing) obtained from the U.S. Census 2022 American Community Survey (ACS) is summarized below.4

3.3.1 Population
Table 3-1, City of Grand Terrace and San Bernardino County Population and Housing Data (2022), provides an overview of the City’s and County’s demographics. The City of Grand Terrace has an estimated population of 13,104 according to the 2022 American Community Survey 5-year estimates. In terms of age demographics, residents under the age of 18 make up 21.4 percent of the City’s population, which is less than that of San Bernardino County at 25.9 percent. The 1 Native Land Digital, https://native-land.ca/, accessed November 7, 2024. 2 City Town Info, Grand Terrace, California, https://www.citytowninfo.com/places/california/grand-terrace, published, accessed November 7, 2024.
3 San Bernardino County, San Bernardino County History, https://main.sbcounty.gov/sbcounty-history/, accessed October 2, 2024. 4 2022 American Community Survey (ACS) 5-year estimates is the most current 5-year data profile available. It represents 60 months of collected data and provides the most reliable and largest data set.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-2
median age of City residents is 37.7 years of age. Comparatively, the median age of San Bernardino County residents is 33.9 years of age. The population of senior citizens in the City is approximately 15.4 percent, which is about 3.5 percent higher than the 11.9 percent of senior citizens in San Bernardino County. Overall, these metrics show that the City has a relatively older population than that of the County.

Table 3-1
City of Grand Terrace and San Bernardino County Population and Housing Data (2022) Category City of Grand
Terrace
San Bernardino
County
Total Population 13,104 2,180,563
Percent of Residents that are children (under 18
years)

21.4% 25.9%
Percent of Residents that are senior citizens (65
and over)

15.4% 11.9%
Median Age (years) 37.7 33.9
Median Household Income $89,781 $77,423
Median House Value (Owner-occupied housing
units w/ a mortgage)
$453,000 $460,500
Occupied Housing Units (Owner-occupied
housing units w/ a mortgage)
1,895 282,198
Percent of Renter-Occupied Housing Units 36.3% 38.9%
Percent of Owner-Occupied Housing Units 63.7% 61.1%
Average Household Size 2.77 3.24
Source: US Census Bureau 2022 American Community Survey 5-Year Estimates, DP04 Selected Housing Characteristics
DP05 Demographic and Housing Estimates
S1901 Income in the Past 12 Months (in 2022 Inflation-Adjusted Dollars) S2506 Financial Characteristics for Housing Units with a Mortgage S1101 Households and Families
The City of Grand Terrace has a higher median household income, home ownership rate, and median house value in comparison to San Bernardino County as a whole. The median household income in the City is $89,781, which is higher than the median income in the San Bernardino County at $77,423. Owner-occupied housing units in the City account for 63.7 percent of total occupied housing which is lower than the 61.1 percent of owner-occupied housing units in the County. The median home value in the City is $453,000 compared to a median home value of $460,500 in San Bernardino County.

The City has a lower average household size of 2.77 compared to the County’s average household size of 3.24.5
Table 3-2, City of Grand Terrace and San Bernardino County Racial and Ethnic Composition (2022), provides an overview of the City’s and County’s racial/ethnic demographics. 5 2022 American Community Survey 5-Year Estimates, S1101 Households and Families, https://data.census.gov/table/ACSST5Y2022.S1101?q=S1101:%20Households%20and%20Families&g=160XX00US0630658, accessed November 7, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-3
Table 3-2
City of Grand Terrace and San Bernardino County Racial and Ethnic Composition (2022) Race or Ethnicity
City of Grand Terrace San Bernardino County
Population Percentage of
Population Population Percentage of Population
White 7,303 55.7 975,461 44.7
Black or African American 592 4.5 171,762 7.9
American Indian and Alaskan
Native
117 0.9 25,467 1.2
Asian 564 4.3 169,063 7.8
Native Hawaiian and Other
Pacific Islander
258 2.0 7,333 0.3
Other Race 2,842 21.7 484,024 22.2
Two or More Races 1,428 10.9 347,453 15.9
Hispanic or Latino (of any
race)1
6,711 51.2 1,200,147 55.0
Total 13,104 N/A 2,180,563 N/A
Source: US Census Bureau, 2022: American Community Survey 5-Year Estimates, DP05 Demographic and Housing Estimates.
1 Hispanic or Latino persons are not counted as a separate racial or ethnic category; persons who identify as Hispanic or Latino are also included in other racial or ethnic categories. Totals may vary slightly due to rounding.

The majority racial/ethnic population in the City of Grand Terrace is white at 55.7 percent of residents. In contrast, the white population of San Bernardino accounts for 44.7 percent. The Asian population of the City constitutes 4.3 percent, which is lower than the 7.8 percent Asian population of the County. Hispanic or Latino persons of any race constitute 51.1 percent of the City’s residents in contrast to 55.0 percent of County residents. Percentages of Black or African American, and American Indian and Alaskan Native are lower in the City compared to the County at -3.4 percent and -0.3 percent respectively. In contrast, Native Hawaiian and Other Pacific Islander populations are 1.7 percent higher in the City compared to the County.

Persons identifying as “other race” account for 21.7 percent of the City’s population, while those reporting two or more races make up 10.9 percent of the City’s population. Percentages of “other race” and two or more races in San Bernardino County are 22.2 percent and 15.9 percent respectively. The overall racial and ethnic composition of the City is less generally diverse than that of the San Bernardino County.

3.3.2 Educational Attainment
Educational attainment is analyzed based on the population of individuals ages 25 and over. The City of Grand Terrace residents have a higher level of educational attainment compared to San Bernardino County; refer to Table 3-3, City of Grand Terrace and San Bernardino Educational Attainment (2022).

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-4
Table 3-3
City of Grand Terrace and San Bernardino County Educational Attainment (2022) Educational Attainment (Age
25 and Over)
City of Grand Terrace San Bernardino County
Population Percentage of
Population Population Percentage of Population
Less than 9th Grade 457 4.9 117,756 8.5
9th to 12th Grade, No Diploma 784 8.4 140,623 10.1
High School Graduate 2,582 27.8 378,034 27.2
Some College, No Degree 2,153 23.2 323,816 23.3
Associate Degree 629 6.8 117,124 8.4
Bachelor’s Degree 1,603 17.3 201,183 14.5
Graduate or Professional
Degree
1,071 11.5 110,197 7.9
Total 9,279 100.0 1,388,742 100.0
Source: US Census Bureau, 2022: American Community Survey 5-Year Estimates, S1501 Educational Attainment.

Totals may vary slightly due to rounding.

Of the City’s population aged 25 years and older, 11.5 percent attained a graduate or professional degree, 17.3 percent attained a bachelor’s degree, and 6.8 percent attained an associate degree.

Thus, about 35.6 percent of the City’s population has completed a higher education degree. In comparison, the County’s higher education degree attainment is as follows: 7.9 percent attained a graduate or professional degree, 14.5 percent attained a bachelor’s degree, and 8.4 percent attained an associate degree. Approximately 13.3 percent of adults in the City of Grand Terrace have not completed high school compared to approximately 18.6 percent of adults in the County.

3.3.3 Employment
According to the 2022 American Community Survey 5- Year Estimate, there are 10,614 residents over 16 years of age in the City of Grand Terrace, and 7,140 were in the labor force. 6 Out of the 7,140 people in the labor force, 6,479 (61.0 percent) were employed and 661 (6.2 percent) were unemployed.

The educational services and health care/social services sector employed the largest number of City residents (21.0 percent), followed by manufacturing (12.4 percent), retail trade (11.0 percent), arts, entertainment, recreation, accommodation and food (9.6 percent), construction (8.4 percent), and other services except public administration. The median household income in the City was $89,781.

While approximately 9.0 percent of employees work from home, a majority of Grand Terrace residents commute for work. The average commute travel time is 32.4 minutes.7

6 2022 American Community Survey 5-Year Estimates, DP03 Selected Economic Characteristics, https://data.census.gov/table?q=DP03%20Selected%20Economic%20Characteristics%20san%20bernardino%20county&g=160XX 00US0630658, accessed October 4, 2024.
7 Ibid.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-5

3.3.4 Housing
According to the US Census Bureau 2022 American Survey 5-Year Estimates, there are 4,973 housing units within the City, 93 percent of which are occupied.8 The most prevalent type of housing within the City of Grand Terrace is single-family detached with about 62 percent of units.9 This is followed by multifamily 5+ units (18.4 percent), multifamily 2-4 units (10.0 percent), mobile homes (6.2 percent), and single-family attached (3.4 percent).10 The primary land uses within the City are residential and open space with a mix of public and commercial uses. Residential land uses are located throughout the City, the majority of these are single-family homes. Open space uses are primarily located at the Blue Mountain along the eastern boundary of the City’s northern boundary and eastern areas of the City.

Industrial uses are primarily in the western side of the City. General commercial also extends from the western portion of the City to the center concentrated along Barton Rd. Office commercial land uses are located in the center of the City as well. Existing (on-the-ground) development within the City limits is identified in Table 3-4, City of Grand Terrace General Plan Acreage by Land Use Category.

The majority of housing units were built in between 1960 to 1989 with 28.7 percent built from 1970 to 1979, 22.6 percent from 1960 to 1969, and 21.5 percent from 1980 to 1989.11 The United States Census Bureau estimates an average household size of 2.77 persons per household.12

3.4 Land Use and Existing Development
Development of the City is guided by its General Plan. The City of Grand Terrace General Plan assigns land use designations to all land located within its incorporated boundaries; refer to Figure 3-1, General Plan Land Use Map. The City is a mix of residential, open space, public, commercial, and industrial uses with residential and open space being the predominant uses. Table 3-4, City of Grand Terrace General Plan Acreage by Land Use Category identifies the current General Plan land use designations and descriptions of the typical uses allowed in each designation.

Table 3-4, City of Grand Terrace General Plan Acreage by Land Use Category provides a general breakdown of acreage by land use designation and its percentage of total area within the City.

Table 3-5, Non-Residential Buildout Calculations defines land use designation in six categories:
residential, commercial, industrial, institutional, open space, and mixed-use. 8 2022 American Community Survey 5-Year Estimates, DP04 Selected Housing Characteristics, https://data.census.gov/table?q=DP04%20Selected%20Housing%20Characteristics%20&g=160XX00US0630658, accessed October 4, 2024.
9 City of Grand Terrace, 2021 – 2029 Housing Element, https://www.hcd.ca.gov/housing-elements/docs/grand-terrace-6thdraft121521.pdf, published 2021, accessed October 4, 2024. 10 Ibid.
11 2022 American Community Survey 5-Year Estimates, DP04 Selected Housing Characteristics, https://data.census.gov/table?q=DP04%20Selected%20Housing%20Characteristics%20&g=160XX00US0630658, accessed November 7, 2024.
12 American 2022 American Community Survey 5-Year Estimates, S1101 Households and Families, https://data.census.gov/table/ACSST5Y2022.S1101?q=S1101:%20Households%20and%20Families&g=160XX00US0630658, accessed November 7, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-6
Figure 3-1
General Plan Land Use Map
Source: City of Grand Terrace, 2010 General Plan, https://www.grandterraceca.gov/departments/planning_development_services/planning, accessed December 12, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-7
Table 3-4
City of Grand Terrace General Plan Acreage by Land Use Category Land Use Category Acres Percent
of Total Land Use Designation
Hillside Low Density
Residential
125 5.5% The hillside areas of Blue Mountain located at the far eastern edge of the City are considered a natural resource that requires special consideration to protect the scenic views and
environmental resources of the mountain. Any development proposed within the Hillside designation will require a special evaluation of all environmental issues and must include provisions for the protection of all natural resources within the area. Properties within the designated areas must demonstrate that building pads and streets can be graded with minimal impact on the hillside and views, and that adequate utilities and public services, including drainage, domestic water, sanitary sewer, and fire protection can be provided. Proposed developments within this area shall be required to prepare a Specific Plan. Clustered development that protects sensitive slopes and natural resources shall be strongly encouraged.

Low Density
Residential (LDR)
Density Range - 0 to
5 dwelling units per
gross acre
884.1 39.2% The Low Density Residential designation limits land uses to single family detached residential units and mobile homes subject to the applicable General Plan policies and Zoning Code provisions. This designation encompasses the majority of property within the City and is largely associated with existing housing developments throughout the City.

Medium Density
Residential (MDR)
Density Range – 6 to
12 dwelling units per
gross acre
181.2 8.0% The Medium Density Residential designation includes both single family detached and multiple family attached developments.

Permitted uses within these areas may include small lot single family developments or attached multi-family developments including townhomes, condominiums, and apartments. Mobile home developments are also permitted. A density bonus may be applied to a project pursuant to the density bonus provisions of Chapter 4.3 of the California Government Code, or pursuant to an approved Planned Residential Development application up to a 20% density bonus may be granted.

Medium High
Density Residential

11.6 0.5% The Medium High Density Residential designation is reserved for multiple family development, with an emphasis on affordable housing projects. This designation may also be applied as an overlay to another land use designation to allow multi-family development at a density of 20 to 24 units/acre as an optional alternative to the base land use designation. A density bonus may be applied to a project pursuant to the density bonus provisions of Chapter 4.3 of the California Government Code, or pursuant to an approved Planned Residential Development application for up to a 20% density bonus.

General Commercial 88.4 3.9% This designation is primarily located along Barton Road and near the I-215 Freeway. It provides for general commercial uses to serve the retail and service needs of the community.

Office Commercial 32.9 1.5% Office commercial uses are used as a buffer between residential areas and general commercial areas. The properties designated for Office Commercial uses are primarily located along Barton Road east of Mount Vernon Avenue and north of Barton Road west of Mount Vernon Avenue. Permitted uses may include office/administrative uses and support retail and service commercial uses.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-8
Land Use Category Acres Percent
of Total Land Use Designation
Light Industrial 107 4.7% Permitted uses for properties designated as Light Industrial include those uses that can be made compatible with other surrounding uses within the City regarding noise, dust, odors, vibration, glare, air quality, traffic, aesthetics, and hazardous materials. Typical uses may include light manufacturing and assembly, small scale warehousing and distribution, research and development, and administrative and service types of uses.

Floodplain Industrial 40.1 1.7% Properties designated with the Floodplain Industrial designation experience the potential for severe flooding resulting from their proximity to the Santa Ana River. Properties within this designation are planned for ultimate development as light industrial, nonpolluting uses similar to the Light Industrial designation. Proposed developments must demonstrate that adequate measures can be implemented to ensure that the proposed use is effectively protected from identified flood hazards. Presently, parcels within this area are largely undeveloped or developed as rural residential land uses. It is anticipated that buildout of this area will occur over a long period of time. During this buildout period, existing residential uses shall be permitted and regulated under the requirements of the Low Density Residential land use designation. Light agricultural uses shall be permitted including the keeping of animals with the approval of an Agricultural Overlay zoning designation.

Hillside Open Space 189.1 8.0% Properties designated as Hillside Open Space are those that should not be developed as urban land uses due to
environmental resources, environmental constraints, or scenic resources. These are primarily located along the western and northern slopes of Blue Mountain. Properties designated as Hillside Open Space shall be retained in their natural condition and used as either natural open space or parkland. They may be either publicly or privately owned.

Mixed Use 93.5 4.2% Properties designated as mixed use are intended to be developed with multiple uses on a single site. This may include residential, commercial, business park, open space, and recreational uses. Compatible uses may be placed horizontally or vertically on the site. All mixed use projects shall be required to submit a Specific Plan or Planned Development that
demonstrates compatibility between the proposed uses as well as buffering from adjacent properties, if warranted. Densities may not exceed those of the residential, commercial, and industrial designations of the General Plan and zoning.

Public 158.9 7.0% Public uses may include schools, parks, the City Hall, City maintenance facilities, and facilities owned and operated by public utilities.

Streets 353.0 15.5% N/A
Total 2,255.1 100% N/A
Source: City of Grand Terrace, Land Use Element, Amended September 27, 2016, accessed October 3, 2024

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-9
Table 3-5
Non-Residential Buildout Calculations
Land Use Designation
Probable
Density
(FAR)
Acres Square
Feet
Square
Feet/Employee
Estimated
Employment
General Commercial 0.35 88.4 1,347,764 500 2,695
Office Commercial 0.35 32.9 501,593 250 2,006
Mixed Use 0.35 78.9* 1,202,909 500 2,405
Light Industrial 0.30 107 1,398,276 1,000 1,398
Floodplain Industrial 0.30 40.1 524,027 1,000 2,422
Open Space N/A 189.1 N/A N/A N/A
Total N/A 495.1 7,397,158 N/A 11,450
*Assumes that 85% of the mixed use area is commercial or business uses.

Table 3-6
Residential Buildout Calculations (Density)
Land Use Designation
Probable
Avg.

Density
Acres Dwelling
Units Persons/Household Estimated Population
Low Density/Hillside 0.7 du/ac 155.3 109 2.83 308
Low Density 3.6 du/ac 885.2 3,183 2.83 9,008
Medium Density 11 du/ac 181.2 1,993 2.83 5,640
Medium High Density 20 du/ac 11.6 230 1.20/2.83 455
Mixed Use 12 du/ac 14.6 175 2.83 495
Total N/A 1,246.8 5,690 N/A 15,906
*Assumes that 15% of the mixed-use area is residential
**Includes existing senior housing in persons per household and estimated population calculations.

3.5 Development Trends and Future Development

3.5.1 Past Land Use, Population Patterns, and Development Trends Since the previous iteration of the 2017 LHMP, land use has not substantially changed within the planning area. The City population nominally increased from approximately 12,040 in the 2010 US Census to 13,104 individuals according to the 2022 US Census. This population increase represents 1,064 people, or an increase of 8.84 percent. This population growth can be attributed to an increase in housing development, as the City’s total housing stock increased from 4,634 to 4,973 units (7.32 percent increase) from 2010 to 2022.13,14 Due to increases in population and major development trends in the planning area in the last five years, local vulnerability to certain hazards has increased; this increase in vulnerability is discussed in this LHMP update.
13 2010 American Community Survey 5-Year Estimates, DP05 Demographics and Housing Estimates, https://data.census.gov/table/ACSDP5Y2010.DP05?q=Grand%20Terrace%20city,%20California, , accessed December 19, 2024. 14 2022 American Community Survey 5-Year Estimates, DP05 Demographics and Housing Estimates, https://data.census.gov/table/ACSDP5Y2022.DP05?q=Grand%20Terrace%20city,%20California, accessed December 19, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-10

3.5.2 Future Land Use, Population Patterns, and Development Trends The City of Grand Terrace General Plan is a key guide for future land use and development. The General Plan (including the Land Use Map) was last updated in 2010. Future growth planning is also documented in the 2021 – 2029 Housing Element, last updated in May 2024. As required by the Regional Housing Needs Allocation (RHNA) determination, the City is required to account for the growth of an additional 630 housing units at varying income levels. The RHNA allocation for 2021 – 2029 for the City is as follows:

Table 3-7
City of Grand Terrace RHNA Allocation
Income Level Percent of AMI* Units Percent
Very Low** Up to - 50% 189 30.0%
Low 51 - 80% 92 14.6%
Moderate 81 - 120% 106 16.8%
Above Moderate 120%+ 243 38.6%
Total N/A 630 100%
Source: SCAG, Housing, https://scag.ca.gov/housing, accessed December 12, 2024. *AMI – Area Median Income
**Includes the extremely low income category, which is estimated as half the VL need pursuant to Government Code Sec. 65583(a)(1)
The RHNA represents the minimum number of housing units the City is required to provide “adequate sites” for zoning and is one of the primary threshold criteria to achieve State approval of the Housing Element. It is noted that the RHNA represents a planning target for new residential growth and is not a building quota.

The City is required to demonstrate the availability of land, zoning provisions, and development standards that facilitate and encourage affordable housing development. The City anticipates accommodating these housing units through projection accessory dwelling units (ADUs), RHNA credits for projects that are in progress, and housing units in and outside of specific plan areas throughout the City. The majority of sites that are identified are outside of major hazard areas, where possible. The City will continue to ensure that proposed projects comply with the latest building and safety requirements and mitigate environmental impacts to the maximum extent feasible.

In addition to the RHNA requirements, the City of Grand Terrace Public Works is currently overseeing the design and construction of various capital improvement projects. See Table 3-8, Capital Improvement Projects, for a description and status of current and future development projects.

The City of Grand Terrace implemented the Gateway at Grand Terrace Specific Plan (Gateway SP) which is a comprehensive development plan for approximately 112 acres and 32 parcels located east of Interstate 215 in the City.15 The Gateway SP site is bounded by Barton Road and vacant land to the north, former Gage Park and industrial uses to the south, Taylor Street and Grand Terrace High School and vacant parcels to the east, and the Burlington Northern Santa Fe railway and industrial/retail uses to the west. The plan is designed to guide future development in 15 CEQA, Gateway at Grand Terrace, https://ceqanet.opr.ca.gov/2021020110/6, received August 1, 2024, accessed December 19, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-11
the area and includes a variety of land uses such as residential, commercial, business park, public utilities, and open space and recreation uses. Future development will also include associated on- and off-infrastructure improvements (roadway improvements, sewer, water, storm drain, and dry utilities), under the guidance of the Project.

Table 3-8
Capital Improvement Projects
Project Location Description Status
West Barton Bridge Replacement
Project
Barton Rd 189 30%
Barton Santa Ana River Rails to
Trails Project
Barton Rd 92 14.6%
Edwin Renewable Fuels Barton Rd and La
Crosse Ave
106 16.8%
La Crosse Site Development La Crosse St. 243 38.6%
Grocery Outlet 22441 Barton
Road
N/A Completed 2020
Source: City of Grand Terrace, Capital Improvement Projects, https://www.grandterraceca.gov/departments/city_managers_office/economic_development/2020_And_Beyond, accessed November 7, 2024.

Additionally, the City reports over an additional 50 development projects listed below and are in various stages of completion:16
• Speed Bumps on W. Carhart
• Barton Road Interchange Project
• Smart Bus Shelter
• Hollywood Video Conversion
• Mt. Vernon Slope Grant
• Mr. TV Video Parking Program
• HISP Program on Mt. Vernon
• High Speed Sign
• City Hall
• Surgical Center
• Preston Traffic Signal
• Commerce Way Expansion
• Lewis Development Phases I & II
• Greens Development Phases I & II
• Dutch Bros Coffee
• Michigan St. Enhancements
• Canal Intersection Redesign
• Development of 4.87 ac. RDA Land
• Canal Path Project with Riverside
• Grand Terrace Health Center
While it remains unlikely that all projected development projects and capital improvement projects listed above will be approved and constructed within the five-year active period of this LHMP, it is reasonable to assume that some level of growth and development will occur. The City is currently experiencing a period of growth and development, focusing on capital improvement projects to revitalize the planning area and fuel economic development. Residential growth within the planning area is accompanied by population growth, increasing local vulnerability to specific hazards. Discussions related to how projected growth could impact risk and vulnerability are discussed on a hazard-by-hazard basis within Section 4.0.

16 City of Grand Terrace, Capital Improvement Projects, https://www.grandterraceca.gov/departments/city_managers_office/economic_development/2020_And_Beyond, accessed February 26, 2025.

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City of Grand Terrace, California
Section 3, Community Profile Page 3-12

3.5.3 Infrastructure Systems
Infrastructure systems within the City of Grand Terrace, such as roadways, water and wastewater facilities, electricity, and natural gas, provide vital community and individual functions. These facilities and distribution systems are primarily owned, operated, and maintained by other agencies. The ability for infrastructure systems to remain operational during hazard events and emergencies will contribute to the City’s ability to withstand or recover sooner from hazard events.

3.5.4 Transportation
The City of Grand Terrace has over 30 miles of streets. The Interstate 215 is a 54.5-mile-long north-south Interstate highway in the Inland Empire region of Southern California. This freeway connects both Riverside and San Bernardino counties. There are two I-215 bridge overpasses in the City of Grand Terrace, one at Barton Road and one at Newport Avenue.

The City of Grand Terrace also has two major freight railroad services that run near the City of Grand Terrace: Union Pacific Railway and BNSF Railway. These railroad services ship food, forest products, automobiles, agricultural products, coal, and chemicals. The Union Pacific has a stop in the City of Colton, located north of the City of Grand Terrace. The BNSF Railway is a major freight railroad network in California and the greater U.S. region. Both freight trains use tracks near Grand Terrace High School, transecting the western portion of the City from north to south.

The City of Grand Terrace has two commuter rail systems, the Metrolink and the Amtrak, that use tracks in the western portion of the City of Grand Terrace. The railway services use tracks intersecting Main Street and adjacent to Grand Terrace High School. All train services use the Burlington Northern and Santa Fe Railroad and Southern Pacific Railroad which traverse the western portion of the City of Grand Terrace from north to south.

3.5.5 Water and Wastewater
The City of Grand Terrace receives water from the Riverside Highland Water Company. The Riverside Highland Water Company sources water from the State that is spread in local groundwater aquifers.17 Additionally about 25 percent of water in the region is imported from Northern California, which supplements the local supply.

The City of Grand Terrace is served by a wastewater system located, owned, and operated by the City of Colton. The water reclamation plant accepts domestic, commercial, and industrial wastewater generated within the Cities of Colton, Grand Terrace and some unincorporated areas of San Bernardino County. The total population discharging to the CWRF is estimated at 65,867 and has average daily flows at the CWRF of 5.6 Million Gallons per Day (MGD).18

3.5.6 Electricity
Southern California Edison (SoCal Edison) provides electricity to the City of Grand Terrace.

Electricity is distributed from power plants through power lines and substations. Substations within the City include the Highgrove Substation (ID SS2381) and Vista (ID SS1638). Power lines within the City are located above ground and underground. Damage to substations or the larger 17 City of Grand Terrace, Utilities, https://www.grandterrace-ca.gov/departments/utilities, accessed October 31, 2024. 18 The City of Colton, Wastewater Information, https://www.ci.colton.ca.us/653/Wastewater-Information, accessed October 3, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-13
distribution system outside of the City could result in power loss to the City. More localized power losses can also occur in the event underground transmission lines are damaged.

3.5.7 Natural Gas
Southern California Gas (SoCal Gas) provides gas service to the City of Grand Terrace. There are no major gas transmission lines traversing the City; however, the City has one high pressure distribution along Interstate 215 in the southwest portion of the City.19

3.5.8 Critical Facilities
The LHMP Planning Committee identified 38 critical facilities for incorporation in the hazard vulnerability/risk analysis; refer to Table 3-9, City of Grand Terrace Critical Facilities, and Figure 3-3, City of Grand Terrace Critical Facilities Map. Critical facilities and facilities of concern are owned, operated, and maintained by various agencies, not just the City. Critical facilities serve an important function in the operations of the municipal government and in serving the community.

These facilities include City Hall, fire station, community center, parks, major transportation systems, water and wastewater facilities, communication facilities, health and medical centers, non-profits, and utility facilities. Damage to these facilities caused by a hazard event has the potential to impair response and recovery and may lead to disruption of services. Critical facilities may also assist in evacuations, serve as assembly points or temporary shelters, or provide a supportive role in preparing for and recovering from hazard events.

Where available, the LMHP Planning Committee identified a facility’s potential loss value, comprised of replacement and contents for each facility. If a facility is completely destroyed in a hazard event, the replacement and contents values indicate the cost to replace the entire facility and all of its contents. Typically, the cost to repair a damaged facility would be less than the replacement value. While the replacement and contents values are used throughout this plan to estimate potential losses, it is noted that the actual cost to recover from a hazard event will depend on the type and magnitude of the event.

19 So Cal Gas, Gas Transmission Pipeline Interactive Map – San Bernardino, https://socalgas.maps.arcgis.com/apps/webappviewer/index.html?id=c85ced1227af4c8aae9b19d677969335, accessed October 3, 2024.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-14
Table 3-9
Grand Terrace Critical Facilities
ID Name Facility Type Community
Lifeline
1 Grand Terrace City Hall
Government
Services Safety and Security
2 San Bernardino County Library Grand Terrace
Branch
Government
Services Safety and Security
3 San Bernardino County Fire Station 23
Government
Services Safety and Security
4 San Bernardino Sherriff Dept Substation
Government
Services Safety and Security
5 Richard Rollins Park Parks & Recreation Safety and Security 6 Veteran's Freedom Park Parks & Recreation Safety and Security 7 Fitness Park Parks & Recreation Safety and Security
8 Griffin Park Parks & Recreation Safety and Security
9 Susan Petta Park Parks & Recreation Safety and Security 10 Gwenn Karger Park Parks & Recreation Safety and Security 11 Grand Terrace Dog Park Parks & Recreation Safety and Security 12 TJ Austin Park Parks & Recreation Safety and Security 13 Grand Terrace Elementary School Public School Safety and Security 14 Terrace View Elementary School Public School Safety and Security 15 Terrace Hills Middle School Public School Safety and Security 16 Grand Terrace High School Public School Safety and Security 17 Grand Terrace Health Care Center Health and Medical Health and Medical 18 Future Health and Medical Health and Medical Health and Medical 19 Blue Mountain Senior Villas Health and Medical Health and Medical 20 San Manuel Indian Health Clinic Health and Medical Health and Medical 21 JC Wallace House Health and Medical Health and Medical 22 SCE Vista Substation Facilities Energy
23 Riverside Highland Water Company Facilities Water Systems 24 RHW Water Tank Facilities Water Systems
25 RHW Water Tank Facilities Water Systems
26 RHW Water Tank Facilities Water Systems
27 Condor Energy Storage Facilities Energy
28 Church of Fire in Christ Non-profit/NGO Safety and Security 29 Azure Hills Seventh-day Adventist Church Non-profit/NGO Safety and Security 30 Grand View Baptist Church Non-profit/NGO Safety and Security 31 Living Word Inland Empire Non-profit/NGO Safety and Security 32 Christ the Redeemer Catholic Church Non-profit/NGO Safety and Security 33 St. Junipero Serra House of Formation Non-profit/NGO Safety and Security 34 Calvary Deaf Church Non-profit/NGO Safety and Security 35 TSG Grand Terrace Yard Facilities Safety and Security 36 Aqueduct Water Systems Water Systems
37 Railroads Transportation Transportation
38 Gage Canal Water Systems Water Systems

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-15
Figure 3-2
Grand Terrace Critical Facilities Map

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-16

3.6 Socially Vulnerable Populations and Determination

3.6.1 SVP Research and Methodology
Identification and integration of Socially Vulnerable Populations (SVPs) into the hazard mitigation planning process is a new addition for the 2025 LHMP and is considered best practice by Cal OES, though no longer required by the most recent 2025 FEMA Local Mitigation Policy Guide.

The purpose of this new LHMP section is to identify vulnerable populations within the planning area by assessing the City’s five census tracts, along with identifying characteristics that can make individuals more vulnerable to natural and human-caused hazards.

CDC Social Vulnerability Index
Social vulnerability is defined by the Centers for Disease Control and Prevention (CDC) as characteristics of a person or group that affect their capacity to anticipate, cope with, resist, and recover from the impact of a discrete and identifiable disaster in nature or society. Several socioeconomic factors or other characteristics influence social vulnerability, as illustrated in Figure 3-3 below.

Figure 3-3
Social Vulnerability Index Themes and Social Factors
Source: CDC and Prevention – National Center for Environmental Health, Planning for an Emergency:

Strategies for Identifying and Engaging At-Risk Groups, published 2015.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-17
US Census and American Community Survey data at the census tract level was utilized to locate and identify socially vulnerable populations within the planning area. The City of Grand Terrace is made up of five census tracts. The LHMP Planning Team evaluated California-based and national environmental justice definitions and data indices as a method for locating and identifying socially vulnerable populations within the City of Grand Terrace.

Figure 3-4, CDC Social Vulnerability Index – Nationwide Comparison (2020), shows the CDC SVI for census tracts within the City. This index was selected because it is most frequently utilized in federal grant evaluations and decision-making, including FEMA hazard mitigation grants. Table 3- 10, Grand Terrace Overall Social Vulnerability Index Scores, shows the SVI score and level of vulnerability for census tracts within the City. Possible scores range from 0 (lowest vulnerability) to 1 (highest vulnerability).

Table 3-10
Grand Terrace Overall Social Vulnerability Index Scores Census Tract Social Vulnerability Index Scores
2022 Statewide Overall SVI Score Level of Vulnerability

71.07 0.8792 High

40.04 0.8421 High

71.09* 0.5658 Medium to High

71.06 0.5701 Medium to High

71.04 0.2886 Low to Medium
*CalEnviroScreen data shows Census Tract 71.11 as 71.09 and was labeled as 71.09 for this table.

Source: Center of Disease Control/Agency for Toxic Substances and Disease Registry, CDC/ATSDR Social Vulnerability Index (SVI), https://www.atsdr.cdc.gov/placeandhealth/svi/interactive_map.html, accessed November 7, 2024.

Four census tracts within the City of Grand Terrace show medium to high and high levels of vulnerability according to the CDC Social Vulnerability Index. The only census tract that does not have high vulnerability is census tract 71.04, with a low to medium level of vulnerability.

Several factors are reported to contribute toward the medium to high vulnerability determinations for census tracts within the City. Census tracts within the City indicate social vulnerability based on 16 indicators identified in the SVI including socioeconomic status, household characteristics, racial/ethnic minority status, and housing type/transportation. The SVI identifies census tracts in the top ten percent (i.e., the 90th percentile) of these demographic, socioeconomic, and housing indicators to indicate a high level of vulnerability.

According to the CDC SVI data, census tracts 40.04, 71.06, 71.07, and 71.11 (listed as 71.09 in Cal EnviroScreen) in the City of Grand Terrace were flagged as facing increased vulnerability for the following indicators:
• Percentage minority
• Persons with no high school diploma
• Percentage of housing cost-burdened occupied housing units (30%+ of income spent on housing costs)
• Percentage of mobile homes

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-18
Figure 3-4
CDC Social Vulnerability Index – Nationwide Comparison (2020)

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-19
Prevalent across all census tracts identified by the SVI as facing increased vulnerability are high percentages of minority populations. Census tracts 40.04 and 71.07 contain the greatest concentrations of minorities at 88.7 and 79.9 percent, respectively. Census tracts 71.06 and 71.11 (71.09 in CalEnviroScreen) also indicated high percentages of minority populations, with more than half of the population in each tract identifying as a minority group. Minority populations may face increased vulnerability during disasters due to potential language or emergency alert barriers if residents do not receive emergency messaging in their native language. In the event of an emergency, evacuation orders and other essential notifications may not reach these groups effectively, placing them at increased risk of injury or death.

Census tracts with the greatest percentage of persons with no high school diploma included census tract 40.04 in the City. Census tract 71.07 also indicates that over a quarter of the population has not attained a high school diploma. This indicates a low level of educational attainment in these portions of the City and an increased level of social vulnerability.

Additionally, census tracts 40.04 and 71.07 indicated the highest percentage of persons living in mobile homes. The population living in mobile homes in Grand Terrace may face increased vulnerability during a hazard event. Vulnerability includes structural weakness of the mobile homes which may not withstand extreme weather conditions. The locations of mobile homes may be built on floodplains or regions of high fire risk. Additionally, residents of mobile homes may have access to fewer resources to recover from disasters.

Lastly, census tract 71.07 contains a high population of persons with housing cost-burdens where 30%+ of their income is spent on housing costs. This population has a higher vulnerability as there is a financial strain to purchase resources for emergency preparedness and to recover from a disaster. Additionally, with resources spent on housing, this may correlate with limited access to transportation making it difficult for residents to evacuate during emergencies.

Based upon the CDC SVI data indicators outlined above, the CDC SVI identifies census tracts

40.04, 71.06, 71.07, and 71.11 (71.09 in Cal EnviroScreen) as facing increased social vulnerability within the planning area. While several other SVI indicators impacted census tracts within the City, the above-mentioned census tracts were identified as facing the greatest social vulnerability.

CalEnviroScreen 4.0
In addition to the CDC Social Vulnerability Index, the LHMP Planning Team utilized the CalEPA DAC criteria based on CalEnviroScreen 4.0 to evaluate the presence of socially vulnerable populations. In May 2022, the California Environmental Protection Agency (CalEPA) used indicators such as pollution burden and population characteristics listed in Table 3-11, CalEnviroScreen 4.0 Indicators. These indicators establish four criteria markers to indicate the presence of a disadvantaged community (DAC) at the census tract level; census tracts meeting one or more criteria are considered disadvantaged. Applicability to the City of Grand Terrace is summarized in Table 3-12, Grand Terrace Disadvantaged Communities Criteria Evaluation, below.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-20
Table 3-11
CalEnviroScreen 4.0 Indicators
Category Indicator
Pollution Burden
Ozone
PM2.5
Diesel
Drinking Water
Lead
Pesticides
Toxicity Release
Traffic
Cleanup Sites
Groundwater Threats
Hazardous Waste
Impacted Water Bodies
Solid Waste
Population Characteristics
Asthma
Low Birth Weight
Cardiovascular Disease
Education
Linguistic Isolation
Poverty
Unemployment
Housing Burden
Source: State of California OEHHA, CalEnviroScreen 4.0 Excel and Data Dictionary, https://oehha.ca.gov/calenviroscreen/maps-data, published October 2021, accessed February 25, 2025.

Table 3-12
Grand Terrace Disadvantaged Communities Criteria Evaluation CalEPA DAC Criteria Applicability to City of Grand Terrace

1. Census tracts receiving the highest 25% of overall
scores in CalEnviroScreen 4.0.

Applicable. Two census tracts within the City
of Grand Terrace are listed with composite
scores at 75 or above. Refer to Table 3-11,
below.

2. Census tracts lacking overall scores in
CalEnviroScreen 4.0 due to data gaps but receiving
the highest 5% of CalEnviroScreen 4.0 cumulative
pollution burden scores.

Not Applicable. No data gaps are listed in
CalEnviroScreen 4.0 for census tracts within
the City of Grand Terrace.

3. Census tracts identified in the 2017 DAC
designation as disadvantaged as required by SB535,
regardless of scores in CalEnviroScreen 4.0.

Applicable. Three census tracts within the
City of Grand Terrace were listed in the 2017
DAC designation. Refer to Table 3-11, below.

4. Lands under the control of federally recognized
tribes.

Not Applicable. No tribal jurisdiction is
located within the City of Grand Terrace
Figure 3-5, CalEnviroScreen 4.0 by Census Tract in Grand Terrace, shows the CalEnviroScreen vulnerability status for census tracts within Grand Terrace and Figure 3-6, 2017 Disadvantaged Communities in Grand Terrace, shows the 2017 DAC designations as required by SB 535.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-21
CalEnviroScreen overall percentile scores and DAC designation based on the CalEPA criteria are summarized in Table 3-13, Grand Terrace Disadvantaged Communities by Census Tract, below.

Table 3-13
Grand Terrace Disadvantaged Communities by Census Tract Census
Tract
Disadvantaged Community Criteria
CalEnviroScreen 4.0
Percentile Score 2017 DAC Disadvantaged Community

40.04 96.02 CalEnviroScreen 4.0 Top 25% Yes

71.07 83.36 CalEnviroScreen 4.0 Top 25% Yes

71.06 69.87 N/A N/A

71.09* 69.02
CalEnviroScreen 3.0
Disadvantaged Communities
Only
Yes

71.04 26.48 No No
*CalEnviroScreen data shows Census Tract 71.11 as 71.09 and was labeled as 71.09 for this table.

Source: California Office of Environmental Health Hazard Assessment, CalEnviroScreen 4.0, https://oehha.ca.gov/calenviroscreen/report/calenviroscreen-40, accessed February 15, 2024.

According to the CalEnviroScreen, two census tracts (40.04 and 71.06) within the City have overall CalEnviroScreen 4.0 percentile scores above 75. Thus, these two census tracts are considered DACs under the first CalEPA DAC criteria. Additionally, census tract 71.09 is considered a DAC under the CalEnviroScreen 3.0 Disadvantaged Communities criteria, establishing census tract 71.09 as a DAC despite the tract’s updated score falling just below the DAC threshold of 70 (at 69.02). While census tract 71.06 received a CalEnviroScreen 4.0 percentile score of 70, the State data does not consider this census tract to be a DAC according to its prescribed indicators. Census tract 71.04 is the only tract in the City with a score lower than 60, making tract 71.04 not a DAC according to CalEnviroScreen data. No data gaps are listed in CalEnviroScreen 4.0 for census tracts, and no tribal jurisdiction is located within the City; these CalEPA criteria do not apply to the City of Grand Terrace.

Of the five census tracts within the City, census tract 40.04 has the highest CalEnviroScreen 4.0 percentile score of 96.02. There are several indicators that impact CalEnviroScreen 4.0 score including ozone, fine particulate matter (PM 2.5), traffic, drinking water, cleanups, groundwater threats, hazardous waste, solid waste, pollution, asthma, low birth weight, cardiovascular, education, and population characteristics. High indicator scores for these environmental effects are correlated with high percentages of health conditions. This census tract is also in a high industrial area zone possibly contributing to the indicators above. Thus, census tract 40.04 is considered a DAC under the first CalEPA DAC criteria.

Census tract 71.07 has the second highest CalEnviroScreen 4.0 percentile score of 83. Indicators impacting its CalEnviroScreen 4.0 score include high ozone, PM 2.5, traffic, clean ups, solid waste, pollution, education, unemployment, and housing burden. This increases vulnerability for hazardous disasters and health conditions for individuals in this area. Census tracts 71.06 and

71.09 may also show vulnerability including one or more indicators such as ozone, diesel, PM2.5, traffic, pollution, education, poverty, housing burden, cardiovascular, low birth weight, and unemployment. Lastly, census tract 71.04 scored the lowest, which means it is not considered a DAC.

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-22
Figure 3-5
CalEnviroScreen 4.0 by Census Tract in Grand Terrace
Source: Cal OEHHA, Cal EnviroScreen 4.0, published October 2021, accessed December 2024

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-23
Figure 3-6
2017 Disadvantage Communities in Grand Terrace
Source: Cal OEHHA, Cal EnviroScreen 4.0, published May 2022, accessed March 2025

Local Hazard Mitigation Plan
City of Grand Terrace, California
Section 3, Community Profile Page 3-24

3.6.2 SVP Determination
Due to the data provided by CalEPA CalEnviroScreen 4.0 and the CDC SVI listed above, the LHMP Planning Team determined that for the purposes of this LHMP, census tracts 40.04. 71.07,

71.06, and 71.11 (listed as 71.09 in CalEnviroScreen 4.0) are considered socially vulnerable populations (SVPs). Based on the CalEPA DAC designation criteria and CalEnviroScreen 4.0 environmental and socioeconomic data, primary concerns include pollution burden, exposures, and environmental effects, as well as sensitive populations and socioeconomic factors indicating DAC and SVPs throughout the City.

The CDC SVI also tracks these data markers to report congregated populations that indicate a high social risk. On an individual level, residents throughout the City may meet one or more of the characteristics listed above that enhance vulnerability within specific hazard circumstances. As this LHMP identifies four census tracts as SVP communities, additional consideration is given at the qualitative data level regarding characteristics that make individuals more socially vulnerable during hazard incidents. This consideration is also integrated into the hazard profiles within Section 4.0, Hazards Assessment.

It is acknowledged that while this geographic area has been identified as facing increased social vulnerability, vulnerable populations do exist within the City and outside of this region. While the presence of many socioeconomic concerns and limitations is present within the community, the scope of the LHMP has limited ability to address or mitigate the underlying causes of such social vulnerability. Rather, this LHMP aims to utilize the data uncovered through the environmental justice indices listed above to establish a more equitable and inclusive LHMP planning process.

Additionally, characteristics include but are not limited to the factors outlined in Figure 3-3, Social Vulnerability Index Themes and Social Factors or in Table 3-11, CalEnviroScreen 4.0 Indicators, As such, the LHMP Planning Team acknowledges that certain characteristics can make individuals throughout Grand Terrace more vulnerable or “high-risk” in specific natural or humancaused hazard incidents.

After understanding the data behind the high vulnerability determination for all census tracts, the LHMP Project Management team worked to incorporate stakeholders into the LHMP Planning Team that represent or serve socially vulnerable groups, including:
• American Red Cross (persons living in poverty, overcrowded households) • Local school districts and institutions of higher education (persons with no high school diploma, persons who speak English less than well)
• City of Grand Terrace Planning & Development Services Department (overcrowding and other housing challenges)
Feedback from these stakeholders and the rest of the LHMP Planning team regarding socially vulnerable populations was included in the hazard profiles (Section 4.0) and mitigation actions (Section 5.0). Specific connections between the risk assessment and relevant mitigation actions are discussed on a hazard-by-hazard basis within Section 4.0, Hazards Assessment.

The first step in developing the vulnerability and risk assessment is identifying the hazards. The LHMP Planning Team reviewed the previously prepared 2017 City of Grand Terrace Hazard Mitigation Plan, hazard mitigation plans from neighboring jurisdictions, and other relevant information to determine the extent of natural and human caused hazards with the potential to affect the City; refer to Table 2-5, Existing Plans, Studies, Reports, and Other Technical Data/Information. A discussion of potential hazards during the first LHMP Planning Team meeting resulted in the identification of the natural hazards that pose a potential risk to the City of Grand Terrace. Table 4-1, City of Grand Terrace Hazard Identification, summarizes the Planning Team’s discussion of each of the natural hazards and indicates those identified for inclusion in the LHMP.

Table 4-1
City of Grand Terrace Hazard Identification
List of Hazards
Identified in
Previous
LHMP
Include in
Updated
LHMP
Discussion Summary
Avalanche No No Not applicable. The conditions for avalanches are not present in Grand Terrace.

Climate Change Yes Yes
Climate change is not profiled as a distinct
hazard, but rather a phenomenon that could
exacerbate hazards. Climate change will be
considered as a factor for relevant identified
hazards.

Coastal Erosion No No
Not applicable. The City is located inland in San
Bernardino County, and there is no coastline
within the jurisdiction. Therefore, the City does
not experience impacts due to coastal erosion.

Coastal Storms No No
Not applicable. The City is located inland in San
Bernardino County, and there is no coastline
within the jurisdiction. Therefore, the City does
not experience impacts due to coastal storms.

Dam Reservoir
Failure No Yes The City is susceptible to inundation caused by dam failure of the Seven Oaks Dam.

Disease/Pest
Management No Yes
Vector-borne and infectious disease has the
potential to impact the planning area. Vectorborne and infectious diseases are profiled along with pandemic under human-caused hazards.

Drought Yes Yes Drought is a potential threat to Grand Terrace and has historically impacted the planning area.

Expansive Soils No No
Soils in the planning area are composed of rock
and loose clay, sand, silt, and gravel, indicating
minimal risk of expansive soils to the City.

Extreme Heat No Yes
Extreme heat has the potential to impact Grand
Terrace. Extreme heat is profiled under severe
weather hazards.

List of Hazards
Identified in
Previous
LHMP
Include in
Updated
LHMP
Discussion Summary
Flood Yes Yes Flood is a potential threat to Grand Terrace and has historically impacted the planning area.

Hailstorm No No
The LHMP Planning Team determined that
hailstorms do not pose a significant risk to the
planning area based upon limited previous
occurrences.

Human-Caused
Hazards No Yes
Human-caused hazards are a potential threat to
Grand Terrace and have historically impacted
the planning area.

Hurricane No No
Not applicable. Hurricanes do not typically
impact California and would not have significant
impacts on an inland City such as Grand
Terrace.

Land Subsidence No No
The LHMP Planning Team determined that this
hazard does not pose a significant risk to the
planning area due to limited previous
occurrences.

Landslide and
Rockfall Yes Yes
Landslide and rockfall are potential threats to
Grand Terrace and have historically impacted
the planning area.

Lightning No No
The LHMP Planning Team determined that this
hazard does not pose a significant risk to the
planning area due to limited previous
occurrences.

Pandemic No Yes
Pandemic is a potential threat and has
historically impacted Grand Terrace. Pandemic
is profiled under human-caused hazards.

Sea Level Rise No No
Not applicable. The City is located inland and
does not experience impacts due to sea level
rise.

Seismic Hazards Yes Yes
Grand Terrace is located in a seismically active
area and seismic hazards including fault
rupture, ground shaking, and liquefaction pose
a risk to the planning area.

Severe Weather
Hazards No Yes
Severe weather including extreme heat, heavy
rains, Santa Ana winds, and power outages
pose a risk to the planning area. These hazards
have been profiled together for organizational
purposes.

Tornado No No
The LHMP Planning Team determined that this
hazard does not pose a significant risk to the
planning area due to the City’s location and
climate.

Tsunami No No
Not applicable. The City is located inland in San
Bernardino County, and tsunami does not pose
a significant risk to the planning area.

Volcano No No Not applicable. There are no active volcanoes that pose a threat to Grand Terrace.

List of Hazards
Identified in
Previous
LHMP
Include in
Updated
LHMP
Discussion Summary
Wildfire Yes Yes
Wildfire is a potential threat to Grand Terrace
and has been included as a potential threat to
the planning area.

Windstorm Yes Yes
Strong winds and windstorms are potential
hazards within Grand Terrace. Strong winds
such as Santa Ana Winds have been detailed
under the severe weather hazards profile.

The LHMP Planning Team used a spreadsheet-based tool to prioritize the identified hazards by assigning each hazard a ranking based on probability of occurrence and magnitude of potential impact. These rankings were assigned based on a group discussion, knowledge of past occurrences, and familiarity with the City’s vulnerabilities. Four criteria were used to establish the hazard priorities to be addressed in the LHMP:
• Probability (likelihood of occurrence)
• Location (size of potentially affected area)
• Maximum Probable Extent (intensity of damage)
• Secondary impacts (severity of impacts to community)
A value from one to four was assigned for each criterion, where one is the lowest and four is the highest. The four criteria were then weighted based on the LHMP Planning Team’s opinion of each criterion’s importance. To enhance collaboration and discussion regarding hazard rankings, the LHMP Planning Team participated in a live survey through Mentimeter, allowing each LHMP Planning Team member to individually report initial thoughts on probability, location, maximum probable extent, and secondary impacts. Rankings were assigned individually based on knowledge of past occurrences and familiarity with City vulnerabilities. The survey was integrated into the LHMP Planning Team Meeting #1 PowerPoint presentation, and all attendees filled out the survey questions. Results were averaged to provide a group score per hazard, utilizing the weighted value (recommended by FEMA and confirmed by the LHMP Planning Team) based on the importance of the criterion; refer to Table 4-2, Hazard Ranking Methodology.

The hazard rankings were multiplied by weighted factors to obtain a score for each criterion. A higher weight was given to the criterion considered more important or significant. For example, the probability of hazard occurrence received a higher weight than the potential secondary impacts. The scores for location, maximum probable extent (anticipated damage), and secondary impacts for each hazard were added together to determine the total impact score. The total impact score was then multiplied by the overall probability score to determine the final score. The final scores were used to determine the prioritization of each hazard based on the following FEMA recommended scale:
• Low Threat: 0 to 12;
• Medium Threat: 12.1 to 42; and
• High Threat: 42.1 to 64.

Table 4-2
Hazard Ranking Methodology
Probability, Location, and Maximum Probable Extent and Secondary Impacts Probability (2.0): Estimated likelihood of occurrence from historical data.

Probability Score
Unlikely – less than 1% probability in next 100 years or has a recurrence interval of greater than every 100 years
1 Somewhat Likely – between 1% and 10% probability in next year or has a recurrence interval of 11 to 100 years
2 Likely – between 10% and 100% probability in next year or has a recurrence interval of 10 years or less
3 Highly Likely – near 100% probability in next year or happens every year 4 Location (0.8): Size of geographical area of community affected by the hazard.

Affected Area Score
Isolated 1
Small 2
Medium 3
Large 4
Primary Impact (0.7): Anticipated damage to a typical facility/structure in the community.

Impact Score
Negligible – less than 10% damage 1
Limited – between 10% and 25% damage 2
Critical – between 25% and 50% damage 3
Catastrophic – more than 50% damage 4
Secondary Impacts (0.5): Estimated secondary impacts to the community at large.

Impact Score
Negligible – no loss of function, downtime, and/or evacuations 1 Limited – minimal loss of function, downtime, and/or evacuations 2 Moderate – some loss of function, downtime, and/or evacuations 3 High – major loss of function, downtime, and/or evacuations 4 Total Score = Probability x Impact, where:

Probability = (Probability Score x Importance)
Impact = (Affected Area + Primary Impact + Secondary Impacts), where:

Affected Area = Affected Area Score x Importance
Primary Impact = Primary Impact Score x Importance
Secondary Impacts = Secondary Impacts Score x Importance Hazard Planning Consideration
Score Range Value Count

0.0 20.0 Low 1

20.1 42.0 Medium 8

42.1 64.0 High 1
The probability of each hazard is determined by assigning a level, from unlikely to highly likely, based on the likelihood of occurrence from historical data. The total impact value includes the affected area, primary impact, and secondary impact levels of each hazard. Each level's score is reflected in the matrix. The total score for each hazard is the probability score multiplied by its importance factor times the sum of the impact level scores multiplied by their importance factors. Based on this total score, the hazards are separated into three categories based on the hazard level they pose to the communities: High, Medium, and Low.

The results from the LHMP Planning Team Meeting #1 survey were compiled and presented to the LHMP Planning Team for further evaluation and discussion. Table 4-3, Hazard Rankings, identifies the final scores and the hazard planning consideration (threat level) for each hazard based on additional discussion with the LHMP Planning Team and the prioritization process described above. Hazards marked with “N/A” denote hazard rankings carried over from the previous LHMP, where running an additional analysis was not determined to be necessary.

Table 4-3
Hazard Rankings
Hazard Type Probability
Impact
Total
Score
Hazard
Planning
Consideration Location Primary
Impact
Secondary
Impacts
Air Quality 2.08 2.10 1.50 1.56 14.60 Medium
Dam/Reservoir Failure
(Seven Oaks Dam) 1.33 1.20 1.10 1.22 6.22 Low
Drought 3.42 3.10 2.50 1.78 35.02 Medium
Flood (riverine,
coastal, localized) N/A N/A N/A N/A N/A Medium
Hazardous Materials 3.08 2.40 2.40 2.78 30.74 Medium
Human-Caused
Hazards 3.08 2.20 2.30 2.44 28.27 Medium
Landslide and
Rockfall 3.17 2.90 3.00 3.11 37.88 Medium
Seismic Hazards N/A N/A N/A N/A N/A High
Severe Weather
Hazards N/A N/A N/A N/A N/A Medium
Wildfire (including
wildfire smoke) N/A N/A N/A N/A N/A Medium
The LHMP Project Management Team decided to identify one hazard (seismic hazards) as a high hazard planning consideration based on conversations with the LHMP Planning Team.

Many hazards identified by the LHMP Planning Team are recognized to be interconnected or interrelated. Where appropriate, the hazard profiles (presented below) may include references to other hazard profiles (such as including extreme heat within the Severe Weather Hazards category).

Additionally, as part of the hazard identification and prioritization process, the LHMP Planning Team determined that some hazards could be combined for clarity purposes within a larger hazard category.

Some hazards were expanded or renamed to reflect conditions more accurately for the City of Grand Terrace. Thus, for example, the Severe Weather profile includes extreme heat, urban heat island effect, heavy rain, and Santa Ana Winds. The Human-Caused Hazards profile includes pandemic, active shooter, power outage/Public Safety Power Shutoff (PSPS), and trail derailment.

It is noted that PSPS is not a direct hazard, but a secondary impact from other natural disasters (primarily Santa Ana Winds, but potentially extreme heat and heavy rains as well). The LHMP Planning Team and survey participants expressed concerns about the ramifications of PSPS and

the effects on City infrastructure and operations; thus, PSPS is discussed under Human-Caused Hazards. The Seismic Hazards profile includes fault rupture/ground motion and liquefaction.

The following hazards are discussed within the 2025 LHMP, below:
• Air Quality
• Dam/Reservoir Failure
• Drought
• Flood
• Hazardous Materials
• Human-Caused Hazards (pandemic, active shooter, power outage/PSPS, and train derailment)
• Landslide and Rockfall
• Seismic Hazards (Fault rupture/ground motion and liquefaction) • Severe Weather Hazards (extreme heat, urban heat island effect, heavy rain, and Santa Ana Winds)
• Wildfire
Climate change has the potential to exacerbate many of the existing hazards in the City. As such, the LHMP Team decided climate change would be included under each applicable hazard profile with a discussion about how each hazard would intersect or become more significant with impacts of climate change. Discussion and analysis related to climate change are discussed as a subsection under each hazard profile included below.

Vulnerability describes how exposed or susceptible to damage an asset is and depends on a number of variables including the asset’s construction, condition, contents, and economic value of functions. A vulnerability analysis predicts the extent of injury/damage on the built environment that may result from a hazard event of a given intensity in a specific area.

The vulnerability assessment considers risks to critical facilities listed in Section 3.0, Community Profile, and to residential and non-residential buildings throughout Grand Terrace. Critical facilities serve an important function in the operations of the municipal government and in serving the community. Critical facilities include essential public buildings, police and fire stations, schools, transportation infrastructure, and essential public utility assets. Many facilities may also be vital to evacuations, serve as assembly points or temporary structures, or provide a supportive role in preparing for and recovering from hazard events. While the City owns and maintains most of the listed critical facilities, there are also critical facilities owned by other public agencies or jurisdictions. Direct and indirect impacts were considered as part of the vulnerability assessment as impacts to some facilities may have indirect impacts on other facilities or populations.

The vulnerability assessment below quantifies, to the extent feasible using the best available data, City assets at risk to hazards and estimates potential losses. This section focuses on the profiled hazards and risks specific to the City of Grand Terrace.

Each hazard profile in the following section includes a Vulnerability and Risk Assessment section that presents the results using the methodology described below. Replacement and content

values for the facilities in each the hazard areas are tallied in each vulnerability table to estimate the total potential losses for each facility.

For each hazard profiled in Sections 4.5 to 4.14, a vulnerability/risk assessment is included within the section. The vulnerability/risk assessment gives equal weight to all hazards, regardless of the identified probability. The specific hazard and associated probability are considered as part of the mitigation prioritization, discussed in Section 5.0, Mitigation Strategy. This assessment considers the physical threats to critical facilities. It should be noted that actual losses will depend on the type, location, magnitude, and extent of the actual hazard event.

This assessment considers the physical threat to the critical facilities, as well as the physical threat to residential and non-residential structures.

Socioeconomic impacts are generally discussed as some hazards have the potential to impact the City in ways beyond physical damages. To confirm at-risk community populations, a detailed parcel analysis investigated the intersection of each mapped natural hazard with development and population vulnerability. The critical facilities listed in Section 3.0, Community Profile, were mapped in GIS and overlaid with mapped hazard areas (those hazards that have a specific or defined geographic area) to determine which assets are located in each hazard area.

Using the comprehensive parcel database from the City of Grand Terrace, parcels with residential and non-residential structures were identified within each mapped natural hazard zone. For residential assets, the number of units is reported per hazard zone. Single family homes are assumed to be one unit. The number of residential units then informs an estimate of residents within each hazard zone. The estimate was generated using the 2.77 persons per household identified by the American Community Survey (ACS) 2022 dataset. For non-residential assets, the total structure square footage was calculated.

Hazard areas and critical facility overlays were conducted for: dam reservoir failure, flood, landslide and rockfall, seismic hazards, and wildfire. It should be noted that the parcel analysis is based on the best available data and is intended for planning purposes only. The City of Grand Terrace provided parcel data via shapefile in November 2024. Michael Baker International did not manipulate the data and used the data as it was provided to estimate hazard vulnerabilities. As such, the parcel analysis serves as an estimate of potential losses based on this data snapshot and may not reflect actual or current conditions within the City at the time of LHMP approval.

Overlays were not prepared for the following hazards: air quality, drought, human-caused hazards (pandemic, active shooter, and trail derailment), and severe weather hazards (extreme heat, urban heat island effect, heavy rain, Santa Ana Winds, and PSPS). These hazards are not geographically defined and/or have the potential to affect the entire City. For the purposes of this LHMP and vulnerability assessment, it is assumed that coastal erosion, drought, human-caused hazards, and severe weather hazards could impact the entirety of the planning area, including all critical facilities.

Replacement and contents values for the facilities and the number of residents and residential and non-residential structures in each hazard area are provided where possible, to estimate the potential losses based on the method described above. Estimations were prepared using replacement values identified in the HAZUS 7.0 Inventory Technical Manual (2025), where

appropriate and related land use categories are listed. Some critical facilities have unavailable replacement cost values due to ownership status or unique characteristics that make replacement estimates infeasible.

The following sections, Section 4.5 through Section 4.14, contain profiles for the hazards identified in Table 4-1, City of Grand Terrace Hazard Identification, above. The profiles include a vulnerability analysis and risk assessment using the methods described in Section 4.3, Vulnerability and Risk Assessment. Each hazard profile is organized by the following subsections:
• Description: A brief introduction to the mechanisms behind the hazard. • Location/Extent: An indication of geographic areas that are most likely to experience the hazard and a description of the potential magnitude and impacts of the hazard. • Previous Occurrences: A highlight of recent and historical occurrences of the hazard accompanied by the impacts or damage to the planning area, if available. • Probability of Future Occurrences: Discussion of the likelihood of the hazard occurring (or a timeframe of recurrence, if available).
• Climate Change: A discussion of how climate change may impact the location, magnitude, recurrence, or extent of the hazard into the future. • Vulnerability and Risk Assessment: A description of the potential magnitude of losses associated with the hazard. Vulnerability may be expressed in quantitative or qualitative values depending upon available data. This section also discusses the changes in vulnerability due to expected growth and development within the planning area. • Socially Vulnerable Populations: A discussion of how the hazard may impact identified socially vulnerable populations within the planning area and considerations that have been incorporated into the mitigation strategy of this LHMP.

Poor air quality can pose a significant risk to the City of Grand Terrace. Air quality can decrease due to air pollution which consists of chemicals or particles in the air that can harm humans, animals, and plants. There are two types of air pollution: anthropogenic and natural sources.

Anthropogenic sources can come from industrial processes, transportation, residential heating, agriculture, waste management, and recreational activities. Industrial processes such as factories, warehouses, and power plants production can emit pollutants such as sulfur dioxide (SO2), nitrogen oxides, and particulate matter (PM). Emissions from transportation such as vehicles, airplanes, and ships, release exhaust gases like carbon monoxide (CO), hydrocarbons and nitrogen oxide. Transportation of goods such as diesel trucking can also contribute to increases in air pollution.1 Agricultural activities such as livestock farming and usage of fertilizers 1 PBS So Cal, Can Banning New Warehouses Improve Air Quality in the Inland Empire?, https://www.pbssocal.org/newscommunity/can-banning-new-warehouses-improve-air-quality-in-the-inland-empire, published May 10, 2022, accessed September 23, 2024.

release methane (CH4) and ammonia (NH3).2
Landfill waste incineration can also produce
methane and other harmful gases.3 Recreational activities such as smoking can release harmful chemicals and particulate matter contributing to air pollution while bonfires and barbecues can also release excess smoke and fine-particle air pollution into the air.4,5Anthropogenic air pollution such as sulfur dioxide (SO2) and nitrogen oxide (NO2) particles can even lead to further hazards such as acid rain. Acid rain occurs when in the air can mix water and oxygen in atmosphere.6 Sulfur dioxide (SO2) and nitrogen oxide (NO2) come mostly from coal-fired power plants and motor vehicles.

Natural sources of air pollution include volcanic ash, dust storms, biological sources, or smoke from wildfires. Volcanic eruptions can emit ash, carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen sulfide (H2S), radon (Rn), hydrogen fluoride (HF), and sulfuric acid (H2SO4) which can be harmful to human health.7 Dust storms can contribute to air pollution by carrying dust and sand particles over long distances, thus increasing particulate matter concentrations.8 Biological sources such as pollen sources, mold spores, and other organic materials can contribute to air pollution. Wildfire smoke is a mixture of gases and fine particles from burning trees, plants, buildings.
9 Wildfire smoke creates fine particulate matter are particles smaller than 2.5 micrometers, which can be inhaled deeply into the lungs. When inhaled, fine particulate matter, also referred to as PM2.5, increases the risk of cardiovascular and respiratory problems. Additionally, wildfire smoke is a complex mixture that consists of other pollutants that have also been shown to lead to a variety of health effects. The most common natural source of air pollution to the City of Grand Terrace may be wildfire smoke as the planning area has potential for severe wildfires as well areas surrounding the City (See Section 4.14, Wildfire).

Air distribution of smoke is affected by factors such as wind, weather, terrain, and fire heat intensity.10 Wind, particularly the Santa Ana winds, may affect wildfire smoke by either clearing out an area or blow more smoke in or fan the flames which can therefore intensify the fire and worsen smoke.11 Intense heat generated by wildfire can drive smoke high into the air where it remains until it cools and beings to descend to ground level however it becomes more diluted and 2 UN Environment Programme, Methane emission are driving climate change. Here’s how to reduce them., https://www.unep.org/news-and-stories/story/methane-emissions-are-driving-climate-change-heres-how-reduce-them, accessed September 18, 2024.
3 United State Environmental Protection Agency, Basic Information about Landfill Gas, https://www.epa.gov/lmop/basic-informationabout-landfill-gas, last updated April 25, 2024, accessed September 18, 2024. 4 National Geographic, Air Pollution, https://education.nationalgeographic.org/resource/air-pollution/, accessed September 18, 2024. 5 United States Environmental Protection Agency, Backyard Recreational Fires, https://www.epa.gov/burnwise/backyardrecreational-fires#:~:text=Outdoor%20recreational%20fires%20can%20become,particle%20pollution%20in%20wood%20smoke., updated June 4, 2024, accessed September 23, 2024.
6 United States Environmental Protection Agency, What is Acid Rain? https://www.epa.gov/acidrain/what-acidrain#:~:text=Acid%20rain%2C%20or%20acid%20deposition,in%20wet%20or%20dry%20forms., last updated May 7, 2024, accessed September 23, 2024.
7 Centers for Disease Control and Prevention, Health Effects of Volcanic Air Pollution, https://www.cdc.gov/volcanoes/riskfactors/index.html#:~:text=and%20your%20health- ,Inhaling%20volcanic%20gases%20and%20ash%20can%20be%20harmful%20to%20your,difficulty%20breathing%20or%20even% 20death., published April 22, 2024, accessed September 23, 2024. 8 World Health Organizations, Sand and dust storms, https://www.who.int/news-room/fact-sheets/detail/sand-and-duststorms#:~:text=Sand%20and%20dust%20storm%20episodes,air%20pollution%20from%20particulate%20matter., published July 11, 2024, accessed September 23, 2024.
9 Centers for Disease Control and Prevention, How Wildfire Smoke Affects Your Body, https://www.cdc.gov/wildfires/riskfactors/index.html, published April 19, 2024, accessed June 28, 2024. 10 United States Environmental Protection Agency, Health Effects Attributed to Wildfire Smoke, https://www.epa.gov/wildfire-smokecourse/challenges-predicting-smoke-concentrations, updated February 2, 2024, accessed June 28, 2024. 11 Ibid.

widespread. Terrain affects smoke concentrations by altering dispersal patterns.12 For example, as the sun warms mountain slopes, air is heated and rises, ultimately bringing smoke and fire with it from lower elevations. After sunlight passes, the terrain cools and the air descend, creating a down-slope airflow that can alter smoke dispersal.

Health effects of air pollution may be relatively minor, such as respiratory irritation, or may be serious and cause significant respiratory problems, heart failure, and death.13 Certain groups of people are more susceptible to the effects of air pollution and wildfire smoke. Particularly vulnerable populations include people with pre-existing health conditions (asthma, chronic respiratory conditions, cardiovascular disease), children 18 and younger, people over the age of 65, pregnant people, outdoor workers, people of color, tribal and indigenous people, and people with low income and/or people experiencing homelessness. Air pollution kills 13 people every minute worldwide as urbanization increases.14 Mitigation efforts can include expanding green spaces and urban tree canopy, promoting public transportation, and regulating industrial emissions.15
The air quality hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area. The specific extent of wildfire smoke may depend on the size and severity of the wildfire as well as weather and wind patterns. Larger wildfires generally create more significant wildfire smoke impacts that extend throughout the County. This may be exacerbated by strong winds which would drive the smoke further throughout the planning area.

Various health impacts are associated with wildfire smoke and poor air quality including coughing, phlegm, wheezing, difficulty breathing, eye irritation, heart failure, and death. Impacts would worsen with increased duration of exposure. Poor air quality and wildfire smoke may impact people even when indoors, leading to health impacts. However, vulnerable populations are most at risk of the health impacts associated with wildfire smoke.16 The extent of poor air quality is measured by the Air Quality Index (AQI). The AQI also focuses on health effects within a few hours or days after breathing polluted air. The EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide.17 The AQI is divided into six categories ranging from good to hazardous (refer to Table 4-5, Air Quality Index).
12 Ibid.
13 United States Environmental Protection Agency, Health Effects Attributed to Wildfire Smoke, https://www.epa.gov/wildfire-smokecourse/health-effects-attributed-wildfire-smoke, accessed June 28, 2024. 14 World Economic Forum, Air pollution is a silent killer. Here’s how cities are tackling it, https://www.weforum.org/agenda/2024/03/air-pollution-is-the-silent-killer-heres-how-cities-are-tackling-it/, published March 18, 2024, accessed September 23, 2024.
15 Ibid.
16 Ibid.
17 National Weather Service NOAA, Air Quality Index, https://www.weather.gov/safety/airquality-aqindex, updated 2024, accessed June 28, 2024.

Table 4-4
Air Quality Index Table
Air Quality
Index
Category Associated Health Impacts
0 – 50 Good Air quality is satisfactory and poses little or no risk 51 – 100 Moderate Sensitive individuals should avoid outdoor activity as they may experience respiratory symptoms
101 – 150 Unhealthy for Sensitive
Groups
General public and sensitive individuals in particular are at risk to experience irritation and respiratory problems
151 – 200 Unhealthy Increased likelihood of adverse effects and aggravation to the heart and lungs among general public
201 – 300 Very Unhealthy General public will be noticeably affected. Sensitive groups should restrict outdoor activities.
301 – 500 Hazardous
General public at high risk of experiencing strong
irritations and adverse health effects. The entire
population should avoid outdoor activities.

Source: U.S. Environmental Protection Agency, Air Data Basic Information, https://www.epa.gov/outdoor-air-qualitydata/air-data-basic-information, updated December 8, 2023, accessed August 9, 2024.

The nearest air quality monitoring stations to the City of Grand Terrace are listed in Table 4-5, Air Quality Monitoring Stations near City of Grand Terrace. Figure 4-1 shows the location of the Table 4-5
Air Quality Monitoring Stations near City of Grand Terrace Name Location Distance From City
ARB #33144 5888 Mission Blvd Riverside, CA 92509 ~5 miles ARB #36203 24302 E. 4th St. San Bernardino, CA 92410 ~5.3 miles ARB #36204 500 N. Dearborn Redlands, CA 92374 ~9.5 miles Source: California Air Resources Board, Air Monitoring Sites, https://ww2.arb.ca.gov/applications/air-monitoringsites-interactive-map, updated 2024, accessed June 26, 2024.https://grandterrace.citynewsgroup.com/articles/thesummer-heat-continues-to-bring-fires-1

Figure 4-1
Air Quality Monitoring Stations near City of Grand Terrace Source: California Air Resources Board, Air Monitoring Sites – Interactive Map, https://ww2.arb.ca.gov/applications/air-monitoring-sites-interactive-map, accessed September 23, 2024.

In 2021, San Bernardino and Riverside counties were ranked first and second most ozone polluted counties in the nation.18 The high rates of asthma, chronic obstructive pulmonary disease, lowered lung function, high blood pressure, and certain cancers dubbed these areas as “diesel death zones” by physicians.19
In 2024, San Bernardino County continued to rank as the number one worst county in the United States for ozone pollution with a weighted average (WA) of 175.2 hazardous days.20 This ranking is followed by Riverside County at 128 WA hazardous days and Los Angeles County 114.8 WA hazardous days.21 Additionally, San Bernardino County ranked number 10 for the worst annual particulate matter in the air.22
In September 2024, San Bernadino County issued a smoke advisory for the Line Fire.23 18 Earth Justice, Fighting to Breathe: Andrea Vidaurre is Taking on the Freight Industry’s Pollution from California to Washington D.C., https://earthjustice.org/feature/andrea-vidaurre-goldman-prize-inland-empire-warehouse, published April 29, 2024, accessed September 17, 2024.
19 Ibid.
20 American Lung Association, State of the Air 2024, https://www.lung.org/getmedia/dabac59e-963b-4e9b-bf0f-73615b07bfd8/Stateof-the-Air-2024.pdf, published 2024, accessed December 18, 2024. 21 American Lung Association, State of the Air 2024, published 2024, https://www.lung.org/getmedia/dabac59e-963b-4e9b-bf0f73615b07bfd8/State-of-the-Air-2024.pdf, accessed September 23, 2024. 22 Ibid.
23 Fox, California’s Line Fire smoke degrades air quality to ‘very unhealthy,’ sends thousands fleeing flames, published September 9, 2024, accessed September 23, 2024.

Several inland empire cities near the City of Grand Terrace have implemented warehouse moratoriums to address air quality concerns.24 This includes San Bernardino, Colton, Redlands, Chino, and Jurupa Valley.

The following table shows PM2.5 readings from the Rubidoux, Mission Blvd air quality monitoring station nearest to the City of Grand Terrace within the past five years:25 Table 4-6
Air Quality in PM2.5 near City of Grand Terrace
Month Year AQI Category Duration (Days)
September 2024 100 ~ 125 Unhealthy for Sensitive Groups 2 July 2024 125 ~ 150 Unhealthy for Sensitive Groups 1
December 2023 100 ~ 125 Unhealthy for Sensitive Groups 1 July 2023 125 ~ 150 Unhealthy for Sensitive Groups 1
December 2021 150 ~ 175 Unhealthy 1
125 ~ 150 Unhealthy for Sensitive Groups 1
100 ~ 125 Unhealthy for Sensitive Groups 2
November 2021 125 ~ 150 Unhealthy for Sensitive Groups 1 100 ~ 125 Unhealthy for Sensitive Groups 1
July 2021 100 ~ 125 Unhealthy for Sensitive Groups 1
October 2020 100 ~ 125 Unhealthy for Sensitive Groups 4 September 2020 150 ~ 175 Unhealthy 1
125 ~ 150 Unhealthy for Sensitive Groups 3
100 ~ 125 Unhealthy for Sensitive Groups 2
November 2019 100 ~ 125 Unhealthy for Sensitive Groups 2 July 2019 100 ~ 125 Unhealthy for Sensitive Groups 1
No federally declared or state declared disasters related to air quality have impacted the planning area within the last five years; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area.

The effects of air pollution are expected to increase in the future due to rapid urbanization and industrialization. Air pollution can damage crops, plants, and forests, where an absorption of large amounts of ground-level ozone may reduce photosynthesis and increase sensitivity to diseases.

Windblown dust may increase from more prolonged droughts.

Air pollution can also increase due to an increase of wildfires. As smoke can travel hundreds or thousands of miles, air quality can also be a problem from the wildfire itself.26 Predicting if air quality will improve or worsen can be difficult because of the unpredictable behavior of wildfires and factors such as wind, weather, and terrain.27 For example, a wind that usually clears out a 24 Daily Reporter, Warehouse boom transformed Inland Empire. Are jobs worth the environmental degradation? 25 World Air Quality Historical Database, Rubidoux – Mission Blvd, Riverside, https://aqicn.org/historical#!city:california/riverside/rubidoux-mission-blvd, accessed September 23, 2024. 26 United States Environmental Protection Agency, Challenges in Predicting Smoke Concentrations, https://www.epa.gov/wildfiresmoke-course/challenges-predicting-smoke-concentrations, updated February 2, 2024, accessed June 19, 2024. 27 Ibid.

valley could also blow more smoke in an area or even fan the flames therefore intensifying the fire and worsening smoke. This may increase the probability of poor air quality due to wildfires.

Based on previous occurrences, there is a somewhat likely probability of future air quality impacts in the future. A somewhat likely probability means there is a 1 to 10 percent probability of occurrence in the next year or a recurrence interval of 11 to 100 years. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with air quality concerns based upon an occasional probability and limited impacts of future events.

Climate change can exacerbate air pollution by increasing the frequency and intensity of wildfires and dust storms. Hot sunny days associated with a warming climate can increase ground-level ozone in some areas.28 Additionally prolonged pollen seasons due to climate change can worsen allergies and respiratory conditions.

As climate change increases the intensity and frequency of wildfires, this will inevitably increase the amount of wildfire smoke. According to the Stanford Center for Innovation in Global Health, about one-third of all particulate matter pollution in the United States comes from wildfire smoke – wildfires that are more intense and common because of climate change.29 Regional wildfires will likely become an increased threat in the City and surrounding areas.

Wildfires release smoke, ash, and other particulate matter that degrade air and water quality.

Thus, fires located in various parts of the City of Grand Terrace and surrounding areas can negatively impact air and water quality throughout the planning area. As such, wildfire mitigation should consider the cumulative impacts associated with climate change.

Poor air quality and wildfire smoke would potentially impact the entirety of the City of Grand Terrace. Thus, all City critical facilities, infrastructure systems, structures, residents, and businesses are considered vulnerable to air quality impacts. The entire City population of 13,104 people and 4,973 occupied housing units are potentially vulnerable. The threat of a major air pollution in Grand Terrace could be derived from transportation, industrial activities, construction sites, wildfires, and residential heating. The I-215 and railroad system serve as transportation corridors, traversing the City and contributing to air pollution while heavy industrial warehouses within and surrounding the City emit volatile organic compounds and sulfur dioxide. It is possible that residents and visitors near these transportation corridors and warehouses may experience worse air quality as opposed to residents and patrons near the City’s open space.30 However, residents near open space may experience greater wildfire smoke if the open space is on fire.

Air pollution does not typically result in immediate physical damage to buildings and infrastructure.

However, pollutants can corrode, discolor, and degrade paint and coatings of buildings over long 28 United States Environmental Protection Agency, Climate Change Impacts on Air Quality, https://www.epa.gov/climateimpacts/climate-change-impacts-air-quality, updated June 4, 2024, accessed September 23, 2024. 29 Stanford Center for Innovation in Global Health, How climate change exacerbates air pollution (and its health impacts), https://globalhealth.stanford.edu/planetary-health-fellowship/how-climate-change-exacerbates-air-pollution-and-its-healthimpacts.html/, published August 24, 2023, accessed June 28, 2024. 30 The Hill, E-commerce hubs worsen air pollution: Study, https://thehill.com/policy/energy-environment/4790958-warehouses-airpollution-increase/, published July 24, 2024, accessed December 23, 2024.

periods of exposure.31 More importantly, air pollution can have serious effects on the health and well-being of humans.

Changes in Vulnerability
Changes in land use, development, and population since the previous 2017 LHMP indicate past changes in hazard vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development for a description of past and future growth within Grand Terrace.

To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth and has initiated various capital improvement projects. Changes in land use and capital improvement projects has enabled residential development and population growth within the planning area. Based on population changes and development trends, it is reasonable to assume that vulnerability to poor air quality and wildfire smoke has increased due to additional population and density across the planning area since the 2017 LHMP.

Anticipated development and capital improvements in the next five years will enable more population growth and increased density within Grand Terrace into the future. Population and residential development are anticipated to increase in accordance with the California Department of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates an additional 630 housing units in the City of Grand Terrace between 2021 and 2029.

Poor air quality has the potential to impact all community lifelines within the City in the future.

Population and density within the City is expected to experience growth and continued development over the 5-year planning horizon of this LHMP. Considering the potential for population growth, additional residential development, increased density, and anticipated capital improvement projects throughout the City, it is reasonable to assume that vulnerability to poor air quality and wildfire smoke will increase over the planning horizon of this LHMP.

Section 3.6, Socially Vulnerable Populations and Determination, includes a detailed determination of socially vulnerable populations (SVP) within the planning and the characteristics that make those populations more vulnerable to hazards. In the City of Grand Terrace, poor air quality may impact socially vulnerable populations sensitive to air quality, particularly concentrated in the northeastern area of the City. Specifically, low-income households, households with cost burdens and overcrowding, elderly residents, children, pregnant women, and individuals with pre-existing health conditions would potentially be affected by air pollution. Residents with pre-existing medical conditions may also face increased economic burdens, inhibiting their ability to move to areas with cleaner air quality and increasing overall health risks. Additionally, mobile home residents and residents with poor HVAC systems to filter air indoors may be more susceptible. This includes areas in census tracts 40.04 and 71.07 where social and economic disparities can further hinder people’s ability to access good air quality, leaving individuals at greater risk of health problems following continuous exposure to poor air quality.
31 RMI, Uncovering the Deadly Toll of Air Pollution from Buildings, https://rmi.org/uncovering-the-deadly-toll-of-air-pollution-frombuildings/, published May 5, 2021, accessed December 12, 2024.

Considerations for SVPs throughout the planning area were incorporated into the mitigation strategy in Section 5.0. Specifically, the LHMP Planning Team tailored Mitigation Actions #8, #11, and #13, to mitigate the socioeconomic impacts of air quality issues that may disproportionately impact SVPs in Grand Terrace.

A dam is an artificial barrier preventing the flow of water or a barrier built across a watercourse for impounding water. Dam failure is the uncontrolled release of impounded water from behind a dam. Flooding, earthquakes, blockages, landslides, lack of maintenance, improper operation, poor construction, vandalism, and terrorism can all cause dam infrastructure to fail. Dam failure results in sudden, fast-moving floods that can damage or destroy property, cause injury or loss of life, and displace large numbers of people in the flood’s path. A dam failure event can also damage regional infrastructure such as transportation and energy networks, causing impacts outside of the immediate inundation zone.

Dam failures are most likely to happen for the following reasons:32 • Overtopping, caused by water spilling over the top of the dam, usually a precursor of dam failure because of inadequate spillway design, debris blockage of spillways, or settlement of the dam crest;
• Foundation defects, including settlement or slope stability; • Cracking caused by natural settling of a dam or seismic movements; • Inadequate maintenance and upkeep; and/or
• Piping, when seepage through a dam is not properly filtered, soil particles continue to progress and form sinkholes in the dam.

Because dam failure can have severe consequences, FEMA and the California Governor’s Office of Emergency Services (Cal OES) require all dam owners of dams classified as "high hazard" and "significant hazard" to develop an Emergency Action Plan (EAP) for warning, evacuation, and post-flood actions. In the event of a major dam failure, mutual aid from all levels of government would be required for an extended period. Recovery efforts would include the removal of debris, clearing roadways, demolishing unsafe structures, assistance in reestablishing public services, and providing continued care for the affected population.

Dams in Grand Terrace are regulated by the Department of Water Resources, Division of Safety of Dams (DSOD). DSOD ensures dam safety by:33
• Reviewing and approving dam enlargements, repairs, alterations, and removals, and ensuring that the dam appurtenant structures are designed to meet minimum requirements;
• Performing independent analyses to understand dam and appurtenant structures performance (including structural, hydrologic, hydraulic, and geotechnical evaluations); 32 Association of State Dam Safety Officials, Dam Failures and Incidents, https://damsafety.org/dam-failures, accessed August 9, 2024.
33 California Department of Water Resources, Division of Safety of Dams, https://water.ca.gov/Programs/All-Programs/Division-ofSafety-of-Dams, accessed July 12, 2022.

• Overseeing construction to ensure work is performed in accordance with approved plans/specifications;
• Inspecting each dam on an annual basis to ensure safety and performance standards; and
• Periodically reviewing the stability of dams/major appurtenances, as well as new findings regarding earthquake hazards and hydrologic estimates in California.

DSOD is responsible for assigning each jurisdictional dam a downstream hazard classification.

This classification is based only on potential downstream impacts to life and property, should the dam fail when operating with a full reservoir. This hazard status is not related to the condition of the dam or the likelihood of the dam to fail in either the short- or long-term. Additionally, dams in southern California usually do not operate at full capacity at all times of the year, and thus hazard risks and classifications are a worst-case scenario assessment. The DSOD definitions for downstream hazards are borrowed from the Federal Guidelines for Inundation Mapping of Flood Risks Associated with Dam Incidents and Failures, and are outlined in Table 4-7, DSOD Downstream Hazard Potential Classification Levels.

Table 4-7
DSOD Downstream Hazard Potential Classification Levels
Downstream Hazard
Potential Classification Potential Downstream Impacts to Life and Property Low
No probable loss of human life and low economic and environmental losses. Losses are expected to be principally limited to the owner’s property.

Significant No probable loss of human life but can cause economic loss, environmental damage, impacts to critical facilities, or other significant impacts.

High Expected to cause loss of at least one human life.

Extremely High Expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 or more.

Source: California Department of Water Resources, Division of Safety of Dams, Definitions of Downstream Hazard and Condition Assessment, https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/AllPrograms/Division-of-Safety-of-Dams/Files/Publications/Division-of-Safety-of-Dams-Definitions-for-DownstreamHazard-and-Condition-Assessment.pdf, accessed July 13, 2022.

Due to the urbanized nature of the City, dam infrastructure is classified as either “extremely high” or “high”. As noted above, this is not reflective of the likelihood for the specific infrastructure to fail; this classification is due to the highly populated areas downstream of the dams. DSOD inspects dams once annually and provides a condition assessment. This condition assessment is a more accurate tool to evaluate infrastructure risk. DSOD uses the National Inventory of Dams (NID) condition rating definitions, with additional criteria, as a guideline in assigning condition assessments. This rating system is outlined in Table 4-8, DSOD Condition Assessment Rating Levels.

Table 4-8
DSOD Condition Assessment Rating Levels
Rating National Inventory of Dams Definitions California DSOD Additional Criteria
Satisfactory
No existing or potential dam safety deficiencies
are recognized. Acceptable performance is
expected under all loading conditions (static,
hydrologic, seismic) in accordance with the
applicable regulatory criteria or tolerable risk
guidelines.

None.

Fair
No existing dam safety deficiencies are
recognized for normal loading conditions. Rare or
extreme hydrologic and/or seismic events may
result in a dam safety deficiency. Risk may be in
the range to take further action.
• Dam has a long-standing
deficiency that is not being
addressed in a timely
manner.
• Dam is not certified and its
safety is under evaluation.
• Dam is restricted and
operation of the reservoir at
the lower level does not
mitigate the deficiency.

Poor
A dam safety deficiency is recognized for loading
conditions that may realistically occur. Remedial
action is necessary. A poor rating may also be
used when uncertainties exist as to critical
analysis parameters that identify a potential dam
safety deficiency. Further investigations and
studies are necessary.

Dam has multiple deficiencies
or a significant deficiency that
requires extensive remedial
work.

Unsatisfactory
A dam safety deficiency is recognized that
requires immediate or emergency remedial action
for problem resolution.

None.

Not Rated
The dam has not been inspected, is not under
State jurisdiction, or has been inspected but, for
whatever reason, has not been rated.

None.

Source: California Department of Water Resources, Division of Safety of Dams, Definitions of Downstream Hazard and Condition Assessment, https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/AllPrograms/Division-of-Safety-of-Dams/Files/Publications/Division-of-Safety-of-Dams-Definitions-for-DownstreamHazard-and-Condition-Assessment.pdf, accessed July 13, 2022.

The geographic extent of dam or reservoir failure is dependent on the type of infrastructure and amount of water stored at the time of the hazard incident. Dams and reservoirs exist throughout San Bernardino County, but none are located within the City of Grand Terrace. The primary dam with inundation zones that may impact Grand Terrace is listed in Table 4-9, Dams and Reservoirs.

Refer to Figure 4-2, Dam Inundation Zone for the location of identified dams and an illustration of inundation extent.

Table 4-9
Dams and Reservoirs
Dam Name Dam Owner
State ID /
National
ID
Latitude,
Longitude
Storage
Qty / Max
Storage
Hazard
Category
Condition
Assessment
Seven Oaks County of San
Bernardino
Department of
Public Works
CA01530 34.11° N,
117.09° W
145,600
Ac-ft
Extremely
High
Satisfactory
Sources: Dam Breach Inundation Map, https://fmds.water.ca.gov/webgis/?appid=dam_prototype_v2 California Division of Safety of Dams, Dams within Jurisdiction of the State of California, https://water.ca.gov/- /media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-of-Dams/Files/Publications/AnnualData-Release/DAMS-WITHIN-JURISDICTION-OF-THE-STATE-OF-CALIFORNIA-LISTED-ALPHABETICALLYBY-COUNTY-SEPTEMBER-2024.pdf, September 2024.

Seven Oaks Dam is located on the Santa Ana River, about 12.5 miles northeast of Grand Terrace.

The structure is a 550-foot-high earth and rock dam with a crest length of 2,980 feet and a capacity of 145,600 acre-feet. Construction of the Seven Oaks Dam was completed in 1999 as a part of the Sant Ana River Mainstream Project. Seven Oaks Dam operates in tandem with the Prado Dam located 40 miles downstream on the Santa Ana River in neighboring Orange County. 34 The Dam is designed to reduce the inflow of 85,000 cfs to 7,000 cfs to provide 350-year flood protection. During rainy seasons runoff is stored behind the dam; small continual releases occur to maintain the water supply downstream. If flooding occurs along the river, the Dam is designed to store water until the lower Prado Dam reservoir level is no longer rising. At the end of the rainy season, the Seven Oaks reservoir is slowly drained. Earthquake resilience was a major consideration during the dam’s construction as it is located between the north and south branches of the San Andreas fault. The Dam was designed to resist damage from an earthquake up to 8.0 on the Richter scale.35
Though Seven Oaks Dam is not located within the city of Grand Terrace, the potential inundation zone in the event of a dam failure could impact the northern and western parts of the city near the Santa Ana River. The downstream hazard potential of the Seven Oaks Dam is considered “Extremely High” according to the DSOD Downstream Hazard Potential Classification system.

Failure of the dam, were it to occur, could cause “considerable loss of human life or would result in an inundation area with a population of 1,000 or more”. Though the downstream impacts of a dam failure are potentially extensive, the likelihood that a dam failure will occur is low. The conditions rating of the Seven Oaks Dam is considered “Satisfactory” meaning that there are no recognized safety concerns by the DSOD.36
34 U.S. Army Corps of Engineers, 7 Oaks Dam, https://resreg.spl.usace.army.mil/pages/7oaks.php, accessed November 13, 2024. 35 Orange County Public Works, Seven Oaks Dam, https://ocip.ocpublicworks.com/service-areas/oc-infrastructure-programs/santaana-river-project/seven-oaks-dam, accessed November 13, 2024. 36 California Department of Water Resources, Division of Safety of Dams, Definitions of Downstream Hazard and Condition Assessment, https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-ofDams/Files/Publications/Division-of-Safety-of-Dams-Definitions-for-Downstream-Hazard-and-Condition-Assessment.pdf, accessed November 14, 2024.

Figure 4-2
Dam Inundation Zone

To date, no significant dam or reservoir infrastructure failures have occurred in or directly impacted Grand Terrace. The most significant dam failures in California history have occurred in other Southern California cities. The closest dam failures to Grand Terrace resulting in significant inundation occurred in the City of Los Angeles, both the St. Francis Dam Disaster of 1928 and Baldwin Hills Dam Disaster of 1963. Both incidents are considered major civil engineering failures and resulted in significant loss of life and property across Los Angeles County. These failures did not impact the City of Grand Terrace.

No federally declared or state declared disasters related to dam or reservoir failure have impacted the planning area within the last five years; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area.

Dam incidents and failures are rare occurrences throughout the region. Considering the lack of dam incidents in the past, the planning team determined that the probability of future dam or reservoir failures is unlikely. An unlikely probability means less than 1 percent probability of occurrence in the next year or a recurrence interval of greater than every 100 years. The LHMP planning team assigned a low hazard planning consideration to the hazards and impacts associated with dam failure based upon an unlikely probability and limited impacts of future events.

Measures are taken to inspect and remediate dams as problems arise. Significant- and highhazard potential dams are periodically inspected by the DSOD; however, dam failures are difficult to predict and dam condition. Reporting is largely the responsibility of the dam owner. Additionally, dam failures may increase in occurrence and severity when coupled with other natural disasters.

Earthquakes or heavy rains can threaten the structural integrity of dam/reservoir infrastructure and create challenging conditions for emergency response operations. Although the probability of a dam failure remains unlikely, the cumulative impacts of related hazards may increase the risk of dam failure in the planning area.

Climate change could indirectly increase the likelihood of dam or reservoir infrastructure failure.

Increased severe storm events and flooding incidents could increase strain on dam and reservoir infrastructure, including dams throughout Southern California. More frequent or intense storms, heavy rains and flooding could increase “wear and tear” and require additional maintenance and infrastructure improvements to protect dam integrity and function. Additionally, severe storm events could oversaturate soils and compromise dam infrastructure.

The Seven Oaks Dam is the primary dam in the area that could potentially pose a threat to Grand Terrace. The inundation zone identified in Figure 4-2 illustrates the parts of the city on the west side of Interstate-215 along South La Cadena Drive could be impacted in the event of a dam failure. The inundation impact area is zoned primarily for the Industrial Floodplain land uses with some Low-Density Single Family Residential. Inundation of this area may result in loss of property and could pose a threat to lives of people living or working in the area. The rest of the City is unlikely to be directly impacted by a dam failure as demonstrated by the inundation hazard zone

in Figure 4-2. Additionally, though the dam has a high downstream hazard level that may put areas outside of the planning area at risk, the likelihood of failure is low.

Approximately 187 residential units are located within the dam inundation hazard zone. The number of vulnerable residential units multiplied by the average 2.77 persons per household for Grand Terrace indicates that approximately 518 people reside in the dam failure hazard zone.

Additionally, approximately 18,599 square feet of non-residential structures are located within the dam failure hazard area. Refer to Table 4-10, Dam/Reservoir Failure Vulnerability Summary for a summary of vulnerable residents, residential units and non-residential buildings.

Table 4-10
Dam/Reservoir Failure Vulnerability Summary
Critical Facilities at Risk
Map ID Name Asset Type Community
Lifeline Replacement Value
35 TSG Grand Terrace
Yard Container Yard Transportation $1,625,800
37 Railroads Railway Transportation Not Available
Populations at Risk
Residents at Risk Residential Units at Risk Non-Residential Area at Risk (Sq.

Ft.)
518 187 18,599
Other than potential inundation of parts of the City, dam failure could have cascading effects including loss of stored water, which might affect water supply and management systems. A dam failure may also have significant impacts to the surrounding natural resources and Santa Ana River. The sudden release of water can lead to severe flooding, which can erode riverbanks, destroy habitats, and displace wildlife. Sediment and debris can alter the river’s flow, further affecting water quality and aquatic ecosystems. Additionally, the loss of the dam’s reservoir can reduce water availability for downstream ecosystems that rely on consistent water levels. Overall, the environmental and economic impacts of a dam failure may occur despite low risk to populations and critical facilities throughout the planning area.

Changes in Vulnerability
Changes in land use, development, and population since the previous LHMP indicate past changes in hazard vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development for a description of past and future growth within Grand Terrace.

To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth while initiating various capital improvement projects. Changes in land use and capital improvement projects have enabled development and population growth within the planning area, particularly in the public facility land use area south of De Berry Street and just north of Pico Street, which narrowly intersect with the dam failure hazard area. Based on population changes and development trends, it is reasonable to assume that vulnerability to dam failure has slightly increased due to population and density increases in the area identified above since the 2017 LHMP.

Anticipated development and capital improvements in the next five years will enable more population growth and increased density within Grand Terrace into the future. Population and

residential development are anticipated to increase in accordance with the California Department of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates an additional 630 housing units in the City of Grand Terrace between 2021 and 2029.

Mapped dam inundation hazard zones narrowly intersect with a public facility land use area (Planning Area 18 of the City’s Specific Plan) in the northwestern portion of the City. Population and density within the mapped dam inundation hazard zone are expected to experience growth and continued development over the 5-year planning horizon of this LHMP. Considering the potential for population growth, additional development, increased density, and anticipated capital improvement projects throughout the City and particularly within areas intersecting with the dam inundation area, it is reasonable to assume that vulnerability to dam inundation will slightly increase over the planning horizon of this LHMP.

Section 3.6, Socially Vulnerable Populations and Determination, includes a detailed determination of socially vulnerable populations (SVP) within the planning area and the characteristics that make those populations more vulnerable to hazards. The dam failure hazard would mainly impact census tracts 40.04 and 71.07 which include Socially Vulnerable Populations (SVPs) within the City and other high-risk individuals located throughout the planning area. While SVPs are particularly concentrated in northeastern areas of the City that are not located within the mapped dam inundation area, vulnerable populations are present in the mapped inundation area including low-income households, minority communities, the elderly, and uninsured residents. SVPs and other high-risk individuals may experience mobility and cost challenges during evacuation efforts or in the event of an injury as a result of a dam failure emergency.

Low-income households in Grand Terrace are more vulnerable during disasters due to limited resources for essential items including food, water, and medical care. Uninsured residents are socially vulnerable, lacking financial means to prepare for or recover from major water damage and destruction following an incident of dam failure. Minority populations face higher rates of chronic health conditions, making them especially at-risk in the event of dam failure. Homeless populations are particularly vulnerable during a nearby dam failure due to a lack of established support systems. Individuals may not be aware of evacuation routes or local emergency procedures, making it difficult for them to respond quickly. Additionally, they might not have access to timely information about the dam failure or the resources needed to cope with the aftermath.

These factors make SVPs throughout City of Grand Terrace especially vulnerable to the impacts of a dam failure.

Drought is defined as a prolonged period of abnormally low rainfall, leading to a shortage of water.

Drought may also be defined by factors other than rainfall, including vegetation conditions, agricultural productivity, soil moisture, water levels in reservoirs, and stream flow. Droughts or water shortages are a gradual phenomenon, often occurring over multiyear periods and increasing with the length of dry conditions. When precipitation is less than normal for a period of time, the flow of streams and rivers declines, water levels in lakes and reservoirs fall, and the depth to water in wells increases. If dry weather persists and water supply problems develop, the dry period can become a drought. The term “drought” can have different meanings depending on how a water deficiency affects day to day activities. Drought is a complex natural hazard, reflected in the following four common definitions:37
• Agricultural – Agricultural drought is defined principally in terms of naturally occurring soil moisture deficiencies relative to water demands of plant life, usually arid crops. • Hydrological – Hydrological drought is related to the effects of precipitation shortfalls on stream flows and reservoir, lake, and groundwater levels. • Meteorological – Meteorological drought is defined solely on the degree of dryness, expressed as a departure of actual precipitation from an expected average or normal amount based on monthly, seasonal, or annual time scales. • Regulatory (or socioeconomic) – Regulatory drought can occur when the availability of water is reduced due to imposition of regulatory restrictions on the diversion and export of water out of a watershed to another area.

Although climate is a primary contributor to hydrological drought, other factors such as changes in land use (i.e., deforestation), land degradation, and dam construction can affect the hydrological characteristics of a region. Because regions are geographically interconnected by natural systems, drought impacts may extend well beyond the borders of the precipitationdeficient area. Changes in land use upstream may alter hydrologic characteristics such as infiltration and runoff rates, resulting in more variable stream flow and a higher incidence of hydrologic drought downstream. Land use changes can alter water shortage frequencies, even when no change in precipitation occurred.38
Droughts cause public health and safety impacts, as well as economic, environmental, and social impacts. Public health and safety impacts are primarily associated with catastrophic wildfire risks and drinking water shortage risks. Examples of other impacts include costs to homeowners due to loss of residential landscaping, degradation of urban environments due to loss of landscaping, agricultural land fallowing and associated job loss, degradation of fishery habitat, and tree mortality with damage to forest ecosystems. Drought conditions can also result in damage to older infrastructure that is located within dry soils with potential to break or crack. Dead or dying vegetation poses a risk to falling and damaging structures and infrastructure systems.

Drought also results in drier brush and an increase in the size and severity of wildfires. Dry brush becomes significantly more flammable and increases the rate of wildfire spread. Extended 37 NOAA, Definition of Drought, https://www.ncdc.noaa.gov/monitoring-references/dyk/drought-definition, accessed August 9, 2024. 38 National Drought Mitigation Center, Drought Basics, https://drought.unl.edu/Education/DroughtBasics.aspx, accessed August 9, 2024.

drought conditions can also create challenges in procuring adequate amounts of water to fight wildfires. Further, water and wastewater infrastructure systems located within areas susceptible to wildfires are at a greater risk of being impacted. Damage or failure to water and wastewater infrastructure systems can significantly reduce or even interrupt service to customers. For more on wildfire hazards, refer to Section 4.14, Wildfire.

Due to the regional nature of water, the geographic extent of a drought in California is not clearly defined. Droughts impact the groundwater that is shared across regions, making this hazard widespread across counties. The drought hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area. As of February 2025, 56% of San Bernardino County is experiencing at least “Severe Drought” conditions according to the United States Drought Monitor.39 Eastern parts of the county are experiencing “Extreme Drought”, which have cascading effects that may impact the rest of the county, including Grand Terrace.

October 2024 was considered the dryest October of the previous 130 years, according to the National Integrated Drought Information System.40
San Bernardino Valley Municipal Water District manages the import of water through the State Water Project. Imported water is delivered directly to residents and is used to replenish the groundwater. The Water District is also responsible for overseeing the extraction of groundwater in the San Bernardino and Colton-Rialto basins, of which Grand Terrace is a part. Riverside Highland Water Company supplies water to the residents of Grand Terrace. The company primarily provides water that has been extracted from local groundwater sources. Persistent drought reduces the rate of groundwater recharge, resulting in a lowered water table.41 This may make it more difficult for local providers to access groundwater. While the city does not directly rely on water imported from northern California through the State Water Project, widespread drought in the state may impact the provision of water to other municipalities in the region. Cities that are impacted by shortages of imported water may begin relying on the same local groundwater supply that is used by the Riverside Highland Water Company.42 This may exacerbate existing stress on the local water supply.

Drought severity and extent depends on numerous factors including duration, intensity, and geographic extent, as well as regional water supply demands by humans and vegetation. The magnitude of drought is usually measured by time and severity of the hydrologic deficit. The United States Drought Monitor provides weekly data identifying portions of the United States that are experiencing drought. The intensity of drought is categorized as one five classifications:
abnormally dry (D0), showing areas that may be going into or are coming out of drought, and four levels of drought: moderate (D1), severe (D2), extreme (D3), and exceptional (D4); refer to Table 4-11, Drought Severity Classification.
39 U.S. Drought Monitor, San Bernardino County, CA,
https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?fips_06071, accessed February 25, 2025. 40 National Integrated Drought Information System, Drought Conditions for San Bernardino County, https://www.drought.gov/states/california/county/San%20Bernardino accessed November 13, 2024. 41 U.S. Geological Survey, Drought and Groundwater Levels, https://www.usgs.gov/special-topics/water-scienceschool/science/drought-and-groundwater-levels, accessed November 8, 2024. 42 The City of Grand Terrace, Be Water Wise Grand Terrace, https://www.grandterraceca.gov/departments/public_works/water_wise, accessed November 8, 2024.

Figure 4-3, Drought Monitor Map, identifies areas of drought by intensity. The Drought Monitor is not a forecast but looks at previous weather patterns; providing a weekly assessment of drought conditions based on how much precipitation did or did not fall.

Table 4-11
Drought Severity Classification
Category Description Possible Impacts
D0 Abnormally Dry Going into drought: short-term dryness slowing planting, growth of crops or pastures. Coming out of drought: some lingering water deficits; pastures or crops not fully recovered.

D1 Moderate
Drought
Some damage to crops, pastures; streams, reservoirs, or wells low, some water shortages developing or imminent; voluntary water-use restrictions requested.

D2 Severe Drought Crop or pasture losses likely; water shortages common; water restrictions imposed.

D3 Extreme
Drought
Major crop/pasture losses; widespread water shortages or restrictions.

D4 Exceptional
Drought
Exceptional and widespread crop/pasture losses; shortages of water in reservoirs, streams, and wells creating water emergencies.

Source: United States Drought Monitor, Drought Classification, https://droughtmonitor.unl.edu/About/AbouttheData/DroughtClassification.aspx, accessed April 1, 2024.

Figure 4-3
Drought Monitor Map
Source: U.S. Drought Monitor, California,
https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?CA, accessed February 25, 2025.

Drought has affected virtually every county in California, with numerous severe droughts over the past century.43According to the 2018 State Hazard Mitigation Plan, from 1972 to 2016, there have been fifteen historical drought State Emergency Proclamations in California.44 Figure 4-4
Historical Drought Conditions for San Bernardino County Source: U.S. National Integrated Drought Information System, California, https://www.drought.gov/states/california/county/san%20bernardino, accessed November 7, 2024 Between the years 2000 and 2024, San Bernardino County has experienced 5 periods of drought where the entire county was experiencing at least “Abnormal Dryness” according to the U.S.

Drought Monitor. “Extreme Drought” conditions were present in four of those events. The most severe drought on record began in 2012 and continued through 2017. On January 17, 2014, the Governor of California declared a state drought emergency, and on April 1, 2015, the Governor announced the first-ever mandatory 25-percent Statewide water use reduction. As part of this reduction effort, the state proposed a series of actions to help save water, increase enforcement to prevent wasteful water use, streamline the State’s drought response, and invest in new technologies that would make California more drought resilient. At the time of the announcement, the volume of Sierra Nevada snowpack was approximately 14 percent of normal.

By the end of May 2014, all of California was in a condition of “extreme” or “exceptional” drought.

At the same time, the volume of the Sierra Nevada snowpack had decreased to less than 10 percent of normal and water stored in Lake Oroville, the major reservoir for the State Water 43 FEMA, Disaster Declarations, https://www.fema.gov/disaster/3023, accessed July 12, 2022. 44 California Governor’s Office of Emergency Services, 2018 California State Hazard Mitigation Plan, https://www.caloes.ca.gov/HazardMitigationSite/Documents/012-2018%20SHMP_FINAL_Ch%209.pdf, published September 2018, accessed July 12, 2022.

Project, was at 58 percent of normal.45 State water restrictions resulted in the City of Grand Terrace limiting outdoor watering to no more than two-days per week, which was down from the previous three-day limit. State water restrictions also required that Riverside Highland Water Company reduce water usage by 36% during this time.46 After a series of winter rains, the Governor issued an executive order in April 2017 ending the drought emergency in Southern California, including San Bernardino County.

The most recent major drought event occurred began in 2020 and prompted a drought state of emergency for much of California.47 Heavy rainfall in the winter of 2023 led to flooding in Southern California and prompted the end of the drought state of emergency in 19 counties including San Bernardino County. 48
One state declared disaster for drought has impacted the planning area within the last five years:
• State of Emergency: Drought Emergency – October 19, 2021.

No federally declared disasters related to drought have impacted the planning area within the last five years; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area.

California weather is classified by a typical dry and wet season. Heavy precipitation that occurs during the wet season constitutes the majority of the annual total rainfall; the absence of any event can significantly impact water availability. Certain atmospheric circulation patterns define California’s temperature and precipitation extremes. Examining these patterns, researchers discovered that atmospheric conditions associated with extreme drought have become increasingly common in recent decades.49
Based on previous occurrences and trends in California, the likelihood that San Bernardino County and the City of Grand Terrace will experience drought conditions in the future is considered likely. A likely probability means between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. The United States Seasonal Drought Outlook depicts large-scale trends based on United States Drought Monitor areas (intensities of D1 to D4), as shown in Figure 4-5, San Bernardino County Seasonal Drought Outlook. It is indicated that drought development is likely to persist throughout the southeastern part of California, including the entirety of San Bernardino County. As the City of Grand Terrace is included within the persistent drought boundary delineated by this map, the City will likely experience the effects of persistent drought in the future. While the region received high levels of precipitation during the December 2022 – January 2023 storms, drought is a known reoccurring hazard within the southern California region. Based on available data and historical, drought is considered to have a high probability for reoccurrence within the City of Grand Terrace and the southern California 45 California Department of Water Resources, California’s Most Significant Droughts: Comparing Historical and Recent Conditions, February 2015.
46 Carl Dameron, Grand Terrace Extends Mandatory Water Restrictions, Grand Terrace City News, November 2015. 47 Executive Department State of California, Proclamation of a State of Emergency https://www.gov.ca.gov/wpcontent/uploads/2021/10/10.19.21-Drought-SOE-1.pdf, published November 2021 and accessed November 8, 2024. 48 Governor Gavin Newsom, Governor Newsom adapts state’s drought response to changing conditions, continues action to support recovery and build resilience https://www.gov.ca.gov/wp-content/uploads/2021/10/10.19.21-Drought-SOE-1.pdf, published September 4, 2024 and accessed November 8, 2024.
49 Stanford News, California drought patterns becoming more common, Stanford scientists say, https://news.stanford.edu/2016/04/01/drought-patterns-change-040116/, published April 1, 2016, accessed November 7, 2022.

region. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with drought based upon a likely probability and expected impacts of future events.

Impacts of future droughts can be mitigated through water conservation efforts and other waterwise management practices taken by water purveyors. Previous occurrences of drought prompted actions to examine water storage, distribution, management, conservation, and use policies more closely. Water purveyors drafted administrative drought actions and implemented mechanisms allowing for administrative consistency in water conservation and drought regulations.

Figure 4-5
San Bernardino County Seasonal Drought Outlook
Source: National Integrated Drought Information System, California, https://www.drought.gov/states/california/county/San%20Bernardino, accessed February 24, 2025.

Climate change is a phenomenon that will likely exacerbate drought hazards. Decreased snowmelt, reduced precipitation, and higher temperatures are all expected effects of climate change. The experiences faced by water supply agencies during the 2012-2017 drought prompted actions to examine water storage, distribution, management, conservation, and use policies more closely. Water districts drafted administrative drought actions and implemented mechanisms allowing for administrative consistency in water conservation and drought

regulations. This interagency coordination and heightened awareness regarding drought helped to mitigate the effects, but the challenges of climate change and drought are ever-present.

According to the 2018 State Hazard Mitigation Plan, climate scientists studying California found that drought conditions are likely to become more frequent and persistent over the twenty-first century due to more frequent and extended periods of high temperature conditions. Decreasing snowmelt, reduced precipitation, and higher temperatures are all expected effects of climate change. As the City relies partially on imported water, climate change impacts (such as decreased snowpack in the Sierra Mountains) on areas outside of the area could affect water supplies within the City. Furthermore, the California Adaptation Planning Guide states that the pressure climate change places on ground water reliance during times of drought is not sustainable.50 When coupled with increasing populations and increasing demand for water in southern portions of California, these conditions may result in future challenges associated with climate change for Grand Terrace and the water purveyors that supply the City’s residents and businesses.

Drought conditions would affect the entire City of Grand Terrace. Thus, all City critical facilities, infrastructure systems, structures, residents, and businesses are considered vulnerable to the impacts of drought. The entire City population of 13,104 people and 4,973 occupied housing units are potentially vulnerable. Droughts do not typically result in physical damage to buildings and infrastructure, thus critical facilities are not at risk of destruction or structural failure. Instead, drought could potentially limit the availability of water supplies to Grand Terrace residents and businesses. Concerns with limited water supplies is the availability to fight wildfire. Furthermore, drought often coincides with the wildfire season and contributes to conditions conducive to wildfire, causing wildfire smoke.

Other effects of drought could be sustained by parks, landscaping, and grounds around commercial and residential facilities, as well as by various plant and animal species, which depend on a delicate meteorological balance to survive. The risk of damage to landscaping and the natural ecosystem, and potential economic impacts from increased water prices or an insufficient supply of water are concerns in addition to the effects of drought on exacerbating wildfire and consequently wildfire smoke conditions.

Changes in Vulnerability
Changes in land use, development, and population since the previous LHMP indicate past changes in hazard vulnerability and can be used to anticipate future changes in vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development, for a description of past and future growth and development within Grand Terrace. To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth and has initiated various capital improvement projects. Historically, drought has not caused physical damage to buildings and infrastructure in Grand Terrace; however, populations and development growth may have exacerbated water supply issues, economic impacts, and the secondary impacts of wildfire risk and environmental challenges associated with drought. 50 California Governor’s Office of Emergency Services, California Adaptation Plan, https://www.caloes.ca.gov/HazardMitigationSite/Documents/CA-Adaptation-Planning-Guide-FINAL-June-2020-Accessible.pdf, published June 2020, accessed July 12, 2022.

Anticipated development and capital improvement projects will enable population growth and increased density within Grand Terrace into the future. Population and residential development are anticipated to increase in accordance with the California Department of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates the need for an additional 630 housing units in Grand Terrace between 2021 and 2029.

Although drought does not typically result in physical damages to buildings and infrastructure, drought conditions would potentially affect the entire City of Grand Terrace. The City anticipates continued growth and development in residential and non-residential areas over the 5-year planning horizon of this LHMP which would also be vulnerable to drought. Population and density increases could exacerbate the impacts of drought such as water supply issues and other economic impacts. Secondary impacts such as increased wildfire risk and the environmental or ecological impacts of drought would potentially affect more people as growth and development within Grand Terrace occurs. Considering the potential for population growth, additional residential development, increased density and anticipated capital improvement projects throughout the City, it is reasonable to assume that vulnerability to drought will increase over the planning horizon of this LHMP.

Section 3.6, Socially Vulnerable Populations and Determination, includes a detailed determination of socially vulnerable populations (SVP) within the planning and the characteristics that make those populations more vulnerable to hazards. The drought hazard would apply to the entirety of the planning area, including Socially Vulnerable Populations (SVPs) within Grand Terrace and other high-risk individuals located throughout the planning area, but particularly those located in northeastern areas of the City. Census tracts with SVPs include tracts 40.04, 71.07, 71.09, and

71.06 where cost burdens associated with potable water surcharges during drought conditions and may need additional outreach and communication for drought awareness purposes.

Low-income households in Grand Terrace are more vulnerable during disasters due to limited resources for essential items including food, water, and medical care. Uninsured residents are socially vulnerable, lacking financial means to prepare for or recover from water scarcity. Minority populations face higher rates of chronic health conditions, making them especially at-risk during droughts. Homeless populations may struggle with sudden water shortages and lack of support services. Strained water supplies can lead to economic impacts and exacerbate wildfires, disproportionately affecting socially vulnerable populations.

Considerations for SVPs throughout the planning area were incorporated into the mitigation strategy in Section 5.0. Specifically, the LHMP Planning Team tailored Mitigation Actions #15 and #16, to mitigate the socioeconomic impacts of drought and water supply issues that may disproportionately impact SVPs in Grand Terrace.

Flooding occurs when a waterway, either a natural one or an artificial drainage channel, receives more water than it is capable of conveying, causing the water level in the waterway to rise.

Depending on how long these conditions last and the amount of water the waterway receives in

proportion to its capacity, the rising water level may eventually overtop the waterway’s banks or any other boundaries to the drainage area, resulting in flooding in the surrounding area.

Floods are the second most common and widespread of all natural disasters faced by the region including the City of Grand Terrace. Floods often occur during heavy precipitation events, when the amount of rainwater exceeds the capacity of storm drains or flood control channels. Floods can also happen when infrastructure such as levees, dams, or culverts fail, or when a section of drainage infrastructure fails, and water cannot be drained from an area fast enough. These failures can be linked to precipitation events (e.g., when water erodes away a levee, allowing water to escape and flood nearby areas), or can be a consequence of other emergency situations (e.g., a dam collapsing due to an earthquake).

FEMA defines flood or flooding as a general and temporary condition of partial or complete inundation of normally dry land areas from:
• The overflow of inland or tidal waters;
• The unusual and rapid accumulation or runoff of surface waters from any source; or, • Mudslides which are proximately caused by flooding and are akin to a river of liquid and flowing mud on the surfaces of normally dry land areas, as when earth is carried by a current of water and deposited along the path of the current. • Collapse or subsidence of land along the shore of a lake or similar body of water as a result of erosion or undermining caused by waves or currents of water exceeding anticipated cyclical levels that result in a flood as defined above.51 Floods can be caused by a number of factors, including:
• Weather and climate patterns (e.g., El Niño, La Niña, Pineapple Express, Atmospheric River, etc.)
o El Niño and La Niña are complex weather patterns resulting from variations in ocean temperatures in the equatorial Pacific. Warmer or colder than average ocean temperatures in one part of the world can influence weather around the globe. El Niño and La Niña episodes typically last 9 to 12 months, but some prolonged events may last for years.52
o Pineapple Express is a name given to an atmospheric river on the West Coast. It is a channel in the atmosphere that moves vast amounts of moisture and can result in massive rain showers.
• Hydrologic features such as reservoirs, ponds, lakes, rivers, etc., can have a large impact on the amount of flooding.
• The absorption capacity of the ground depends on the composition of soil and bedrock of the area. Less absorbent soil conditions in addition to lack of proper storm infrastructure can result in flooding.
• Type and density of vegetation is related to moisture absorption affecting the flow of water. • Patterns of land use/urbanization relates to the pervious and impervious nature of the ground.
51 FEMA, Glossary: Flood,
https://www.fema.gov/glossary/flood#:~:text=A%20general%20and%20temporary%20condition,inland%20or%20tidal%20waters%3 B%20or, updated July 7, 2020, accessed July 1, 2024.
52 NOAA, What are El Nino and La Nina?, https://oceanservice.noaa.gov/facts/ninonina.html, updated June 16, 2024, accessed July 1, 2024.

• Expected level, age, and condition of flood management infrastructure can impact flooding conditions.
• Large-scale wildfires dramatically alter the terrain and ground conditions. Vegetation absorbs rainfall, reducing runoff. However, wildfires leave the ground charred, barren, and unable to properly absorb water, creating conditions ripe for flash flooding and debris flow.

Flood risk remains significantly higher until vegetation is restored – up to five years after a wildfire.53
The City of Grand Terrace is prone to two primary types of flooding:
• Riverine: riverine flooding occurs when streams and rivers exceed the capacity of their natural or constructed channels to accommodate water flow and water overflows the banks spilling out into adjacent low-lying, dry land.54 According to the FEMA National Risk Index, the City of Grand Terrace has a relatively moderate risk of riverine flooding.55 • Localized: localized flooding is the result from storms and run off that overload the drainageways and flows into streets and low lying-areas.56 This type of flooding can block streets, and low-lying areas while flooding homes and businesses such as the lower parts of the floors and basements. Localized flooding tends to recur small impacts accumulated over time which can become major problems in the future.

Floods can cause extensive damage and pose health risks. The force of a flood is sufficient to carry away large objects and damage structures, causing considerable damage to buildings and infrastructure. In severe instances, floodwaters themselves can destroy structures or move them off their foundation. Floods can saturate and weaken soil, potentially making structures built on them more susceptible to damage or collapse. Flooding can also affect water quality, as large volumes of water can transport contaminants into water bodies and overload storm/wastewater systems. Additionally, large increases in water volume can cause water body erosion and loss of aquatic habitat. Flooding can also cause economic loss to people and government due to the destruction of property and/or infrastructure. Flood events may be particularly destructive when they create conditions conducive to geologic hazards including landslides or debris flows.

Shallow flooding, a type of localized flooding, can also pose health problems to the community.57 This includes:
• Triggering the growth of mold and mildew in buildings which aggravate allergies and asthma.
• An influx of snakes and rodents moving into closer contact with people. • Movement of gasoline, pesticides, fuel oils, chemicals and other substances can be washed into buildings and soaking into soils.
• Breeding of vectors in standing still water which can transmit encephalitis and West Nile Virus, straining individuals and families with strain on individuals and family. 53 FEMA, Flood Risk Increases After Fires Are Out – Buy Flood Insurance Now, https://www.fema.gov/fact-sheet/4562/flood-riskincreases-after-fires-are-out-buy-flood-insurance-now, published October 21, 2020, accessed July 12, 2022. 54 FEMA, Riverine Flooding, Riverine Flooding, https://hazards.fema.gov/nri/map , accessed July 23, 2024. 55 FEMA, Riverine Flooding National Risk Index, https://hazards.fema.gov/nri/map, accessed July 23, 2024. 56 Reducing Damage from Localized Flooding: A Guide for Communities, Chapter 2: Localized Flooding, FEMA511 ch2.indd, accessed July 23, 2024.
57 Ibid.

Although nearly all of the City of Grand Terrace is elevated along the base of Blue Mountain, the northwest portion of the City lies within a designated flood plain of the Santa Ana River. Levees have been constructed along a portion of the City’s riverfront. However, a flood hazard continues to exist that could make certain areas unsuitable for habitable structures. There are also localized flooding issues occurring outside of the floodplain in areas such as Pico St. Additionally, the City is prone to flooding in the following areas:
• All of Pico St from east to west City limits and sections of Michigan Street near Pico Street floods often.
• Flooding occurs at Vivienda Avenue and Burns Avenue.
• Runoff from Highway 215 runs into the creek bed running parallel to Vivienda Ave and will flood Grand Terrace Road during extensive periods of rain, making the road impassible. • The natural basin/creek bed southeast of Thompson Drive floods during heavy rain.

FEMA flood maps indicate that a few locations in the northwestern corner of the City between the railroad tracks and bordering S La Cadena Drive are at an elevated risk for flooding; refer to Figure 4-6, Flood Hazard Zones. This figure includes illustrative data derived from FEMA Digital Flood Insurance Rate Maps (DFIRM) within the City of Grand Terrace. Refer to Appendix C for a record of the City’s FIRM maps. The City currently has no record of repetitive loss of properties due to flooding.

The extent or magnitude of flooding is measured by percentage and annual chance floods. The flooding areas are classified as 1 in 100 (one percent) or high risk, and 1 in 500 (0.2 percent) or moderate risk of flooding. Areas having a chance of less than 0.2 percent are classified as low risk areas. Floods are measured by stream gages that are installed in bodies of water near populated areas. They are installed and operated by the United States Geological Survey (USGS) and continuously monitor water levels.

Table 4-12
Flood Zones Definitions
Zone Risk
Floodplain – 100-year flood zone (A, AE, AH, AO,
VE)
1% annual flood risk
Floodway – 100-year flood zone (AE) 1% annual flood risk 500-year flood zone 0.2% annual flood risk
Area with reduced flood risk due to levee Reduced flood risk Source: FEMA, FEMA Flood Maps and Zones Explained, https://www.fema.gov/blog/fema-flood-maps-and-zonesexplained, accessed August 23, 2023.

Figure 4-6
Flood Hazard Zones

While San Bernardino County has experienced a significant number of flood events since the previous HMP, very few flood events have recently been recorded as directly affecting the City of Grand Terrace. Notable flood events affecting the City of Grand Terrace within the last five years are detailed below:

In August 2023, Hurricane Hilary (later downgraded to a tropical storm) swept across Southern California. The storm brought widespread flooding, heavy rain, severe winds, and other impacts to numerous communities in Southern California. In the City of Grand Terrace, the Sisters of St.

Benedict Labyrinth experienced downed trees and other impacts due to heavy rains during the storm.58
Six state declared disasters related to flood have impacted the planning area within the last five years:
• State of Emergency: Severe Winter Storms – December 30, 2021 • State of Emergency: Tropical Storm Kay – September 16, 2022 • State of Emergency: Severe Winter Storms – January 10, 2023 • State of Emergency: Severe Winter Storms – March 1, 2023 • State of Emergency: Tropical Storm Hilary – August 19, 2023 • State of Emergency: Severe Winter Storms – February 4, 2024 Several federally declared disasters related to flood have impacted the planning area within the last five years. A list of federally declared disasters related to flood is included below; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area for further details regarding specific impacts (if any) to the City of Grand Terrace.59 • DR-4750-CA: Tropical Storm Hilary – November 21, 2023 • DR-3592-CA:Severe Winter Storms, Flooding, Landslides, and Mudslides – March 10, 2023
• DR-3591-CA:Severe Winter Storms, Flooding, Landslides, and Mudslides – January 9, 2023
FEMA defines flood zones based on the probability of occurrence, expressed in a percentage of the change of a flood of a specific extent occurring in any given year. For areas located within the 100-year flood zone, there is a 1 percent chance in a given year that this area will be inundated by flood waters. For moderate flood hazard areas located within the 500-year flood zone, this probability decreases to 0.2 percent. For minimal flood hazard areas, they are located outside of the 0.2 percent annual chance flood.

Given the location of the planning area and based on previous flood events, there is an unlikely probability of a flood event significantly affecting the City of Grand Terrace. An unlikely probability means there is a less than 1 percent probability of occurrence in the next year or a recurrence 58 Luna, Deborah, Grand Terrace Labyrinth Affected by Hurricane Hilary, https://www.citynewsgroup.com/articles/grand-terracelabyrinth-affected-by-hurricane-hilary-, accessed August 22, 2024. 59 FEMA, Disaster Declarations for States and Counties, https://www.fema.gov/data-visualization/disaster-declarations-states-andcounties, accessed August 9, 2024.

interval of greater than every 100 years. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with flood events based upon a likely probability and expected impacts of future events.

Climate change is likely to have a direct effect on flooding. According to research conducted by the University of California, Los Angeles, California will experience extremely wet and extremely dry seasons by the end of the century. It is predicted that “over the next 40 years, the State will be 300 to 400 percent more likely to have a prolonged storm sequence as severe as the one that caused the legendary California flood more than 150 years ago.”60 This research team confirmed the recent findings from a New York Times article titled “The Coming California Megastorm,” predicting a future superstorm exacerbated by climate change. A warmer climate can carry atmospheric rivers in rapid succession to California, testing the capacity of dams and flood control infrastructure. The risk of a month-long megastorm as modeled and visualized by this article has a one in 50 chance of occurring annually. If global temperatures continue to climb, the likelihood of such a storm could increase to one in 30.61 Thus, flood considerations should continue to remain a mitigation priority into the future.

As mentioned above, climate change is expected to continue to disrupt traditional weather patterns, thereby increasing the prevalence of extreme weather events across the nation and within the City of Grand Terrace. Changing weather patterns and other impacts of climate change may change the identified flood zones within the planning area in the coming years, potentially increasing the risk to the local population and City assets.

Critical facilities located within the flood hazard zone include those that serve as transportation community lifelines. In total, there are two vulnerable critical facilities located within the City’s flood hazard zone. A container yard and railroad tracks are the asset types that been identified as vulnerable to the flood hazard. Critical facilities located within the City’s identified flood hazard zone have been listed in Table 4-13, Flood Vulnerability Summary.

Approximately 3 residential units are located within the flood hazard zone. The number of vulnerable residential units multiplied by the average 2.77 persons per household for Grand Terrace indicates that approximately 8 people reside in the flood hazard zone. Additionally, approximately 2,167 square feet of non-residential structures are located within the flood hazard area. Refer to Table 4-13, Flood Vulnerability Summary for a summary of vulnerable residents, residential units and non-residential buildings.

Table 4-13
Flood Vulnerability Summary
Critical Facilities at Risk
Map ID Name Asset Type Community
Lifeline Replacement Value
35 TSG Grand Terrace
Yard Container Yard Transportation $1,625,800
60 UCLA Newsroom, Study forecasts a severe climate future for California, https://newsroom.ucla.edu/releases/california-extremeclimate-future-ucla-study, accessed July 12, 2023. 61 New York Times, The Coming California Megastorm, https://www.nytimes.com/interactive/2022/08/12/climate/california-rainstorm.html, published August 12, 2022, accessed July 2, 2024.

Critical Facilities at Risk
37 Railroads Railway Transportation Not Available
Populations at Risk
Residents at Risk Residential Units at Risk Non-Residential Area at Risk (Sq.

Ft.)
8 3 2,167
Potential impacts of a flood event in the City would include significant damage to buildings and infrastructure, including transportation community lifelines. Specific critical facilities located within the flood hazard zone include a container yard and railroad tracks. Damages to these assets would hinder City operations, emergency response, and local transportation operations. A flood event would also potentially result in damaged homes and businesses. Potential impacts would include the displacement of a significant number of people, disruption of power, water, and emergency services, economic losses, and increased insurance premiums. Major transportation routes, including Interstate 215 and railroads, could become severely congested or inaccessible, complicating evacuation efforts, especially for socially vulnerable populations. Floodwaters could cause medical emergencies, hindering residents and visitors from leaving the hazard area, and potentially affecting the health of nearby populations as floodwaters spread. Shelters designated for emergencies might be damaged or inaccessible, increasing the risk of secondary hazards like waterborne diseases for the local population.

Depending upon the extent and magnitude of a flood event, streets may be inundated with multiple feet of flood water due to urban flooding. Businesses may be forced to close, and City streets may no longer be accessible. Flood waters may also wash out City roads including South La Cadena Drive, cutting off evacuation access. Socially vulnerable populations with limited mobility could face additional vulnerability during a major flood event as they are unable to escape from incoming flood waters.

In the event of a major 100-year flood event, impacts to critical facilities in the planning area could cause disruption in essential services and the potential pollution of local water sources. While drowning is the primary cause of death during a flood event, flood waters may contain sharp objects that can cause additional injury and lead to infection for those impacted by a flood emergency.

Changes in Vulnerability
Changes in land use, development and population since the previous LHMP indicate past changes in hazard vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development for a description of past and future growth within Grand Terrace.

To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth and has initiated various capital improvement projects. While changes in land use and capital improvement projects have enabled residential development and population growth within the planning area, industrial areas intersecting with the flood hazard area have not experienced this same growth. Based on the lack of development and population increase within the floodplain, it is reasonable to assume that vulnerability to flood has remained the same since the 2017 LHMP.

Anticipated development and capital improvements in the next five years will enable more population growth and increased density within Grand Terrace into the future. Population and residential development are anticipated to increase in accordance with the California Department

of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates an additional 630 housing units in the City of Grand Terrace between 2021 and 2029.

Mapped flood hazard zones primarily include the floodplain industrial land use zone in the northwestern portion of the City. Population and density within the mapped flood hazard zone are not expected to experience growth or development over the 5-year planning horizon of this LHMP.

Considering these factors, it is reasonable to assume that vulnerability to the flood hazard will remain relatively the same over the planning horizon of this LHMP.

Section 3.6, Socially Vulnerable Populations and Determination, includes a detailed determination of socially vulnerable populations (SVP) within the planning area and the characteristics that make those populations more vulnerable to hazards. The flood hazard would apply to areas in the northwestern part of the City near the Santa Ana River, including Socially Vulnerable Populations (SVPs) within Grand Terrace and other high-risk individuals. Census tracts 40.04, 71.07, 71.09, and 71.06 are ranked as “High” and “Medium High” on the CDC Social Vulnerability Index and include SVPs particularly minority populations, low-income households, limited English proficiency individuals, the elderly, and uninsured residents. SVPs and other high-risk individuals may experience mobility and cost challenges during evacuation efforts or in the event of an injury as a result of a major flood event.

Low-income households in Grand Terrace are more vulnerable during disasters due to limited resources for essential items including food, water, and medical care. Uninsured residents are socially vulnerable, lacking financial means to prepare for or recover from major water damage and destruction following a flood event affecting themselves and their property. Minority populations face higher rates of chronic health conditions, making them especially at-risk in the event of flooding due to the risk of water-borne disease. Homeless populations are particularly vulnerable during a flood event due to a lack of established support systems. They may not be aware of evacuation routes or local emergency procedures, making it difficult for them to respond quickly to incoming floodwaters. Additionally, they might not have access to timely information, or the resources needed to cope with the aftermath. These factors make SVPs throughout City of Grand Terrace especially vulnerable to the impacts of flooding.

Considerations for SVPs throughout the planning area were incorporated into the mitigation strategy in Section 5.0. Specifically, the LHMP Planning Team tailored Mitigation Actions #18 and #26,to mitigate the socioeconomic impacts of flood that may disproportionately impact SVPs in Grand Terrace.

A hazardous material is a substance that, because of its quantity, concentration, or physical or chemical composition, poses a significant present or potential hazard to human health and safety or to the environment if released. A release may occur by spilling, leaking, emitting toxic vapors, or any other process that enables the material to escape its container, enter the environment, and

create a potential hazard.62 Hazardous materials can be in the form of explosives, flammable and combustible substances, poisons, and radioactive materials. Hazardous material accidents can occur during production, storage, transportation (roadway and railway), use, or disposal.63 Transportation of hazardous materials may pose a risk to people, property, and the environment.

Vehicles, trains, boats, and aircraft may be used to transport these materials, and accidents may result in the release of hazardous materials. Additionally, an unrelated disaster such as an earthquake or flood may damage hazardous material storage or distribution infrastructure.

Incidents can also occur independently of other disasters, such as from human error or malfunctioning or broken equipment.

The impacts of a hazardous materials release can vary depending on the type and amount of material released. Hazardous materials exposure can include the following effects: skin/eye irritation; difficulty breathing; headaches; nausea; behavior abnormalities; cancer; genetic mutations; physiological malfunctions (i.e., reproductive impairment, kidney failure); physical deformations; or birth defects.64 Hazardous material spills can release significant amounts of hazardous material in which the release cannot be controlled.65 Hazardous material spills can be detrimental to wildlife and aquatic ecosystems. Certain hazardous substances also have the potential to explode or cause fires, threatening both animals and human populations.66 Hazardous materials are generated, used, and stored by facilities throughout the City for a variety of purposes in service industries, businesses, schools, and households. Hazardous materials associated with certain commercial, industrial, and manufacturing uses are present throughout the City. Additionally, household hazardous materials are commonly found in paints, lawn and garden products, household cleaners, beauty products, medicine, automotive fluids, and batteries. These hazardous materials are generally associated with low-risk, small-scale operations consistent with day-to-day activities and would be present throughout developed areas of Grand Terrace and participating jurisdictions.

Certain areas throughout the City have a higher risk of hazardous materials spills. Hazardous materials transportation corridors including highways and navigable waterways are potential highrisk areas. As such, hazardous materials incidents may be caused by a traffic accident along Highway 215, which runs through the City. The hazardous materials hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area.

The Federal Motor Carrier Safety Administration (FMCSA) defines the following classes of hazardous materials:67
62 Washington Emergency Management Division, Hazardous Material, https://mil.wa.gov/hazardous-material, published 2024, accessed April 17, 2024.
63 Department of Homeland Security, Chemicals and Hazardous Materials Incidents, https://www.ready.gov/hazardous-materialsincidents, accessed April 17, 2024. 64 US EPA, Health and Ecological Hazards Caused by Hazardous Substances, https://www.epa.gov/emergency-response/healthand-ecological-hazards-caused-hazardous-substances, updated December 13, 2023, accessed April 17, 2024. 65 Ball State University, Hazardous Material Spills, https://www.bsu.edu/about/administrativeoffices/emergencypreparedness/guidelines/hazardous-materialspills#:~:text=A%20hazardous%20material%20spill%20is,the%20substance%20cannot%20be%20controlled., published 2024, accessed April 12, 2024.
66 United States Environmental Protection Agency, Health and Ecological Hazards Caused by Hazardous Substances, https://www.epa.gov/emergency-response/health-and-ecological-hazards-caused-hazardous-substances, accessed April 12, 2024. 67 FMCSA, National Hazardous Materials Route Registry - By State, https://www.fmcsa.dot.gov/regulations/hazardousmaterials/national-hazardous-materials-route-registry-state, accessed August 22, 2024.

• Class 1: Explosives
• Class 2: Gas
• Class 3: Flammable Liquid
• Class 4: Flammable Solid
• Class 5: Organic
• Class 6: Poison
• Class 7: Radioactive
• Class 8: Corrosives
• Class 9: Dangerous (Other)
• Class (i): Poisonous Inhalation Hazard (PIH)
The California Environmental Protection Agency (CalEPA) works to develop, implement, and enforce environmental laws to regulate air, water and soil quality, pesticide use and waste recycling and reduction. CalEPA maintains a database of regulated facilities that include sites producing or related to the use of hazardous materials. Figure 4-7, Sites Related to Hazardous Materials in the City of Grand Terrace, includes the sites identified within Grand Terrace.

Figure 4-7
Sites Related to Hazardous Materials in the City of Grand Terrace Source: CalEPA, CalEPA Regulated Site Portal, https://siteportal.calepa.ca.gov/nsite/map/results, accessed August 22, 2024.

Note: Red circle indicates the approximate location of the City of Grand Terrace.

Hazardous materials sites are concentrated around developed areas of Grand Terrace.

Specifically, sites storing hazardous materials are heavily concentrated along the south side of Barton Road, along with sites scattered in various areas including near Terrace Hills Junior High School and near the corner of Van Buren Street and Michigan Avenue. Additionally, hazardous materials transportation corridors including I-215 and the railroad tracks running through the western limits of the City are potential areas of concern.

The magnitude and severity would be dependent on the type of spill, location, and the extent to which hazardous materials are released. Hazardous materials can be flammable, radioactive, infectious, corrosive, toxic/poisonous, or otherwise reactive. For example, a radioactive material spill would have a much further-reaching extent when compared to a paint spill. Climate conditions can also affect the severity of hazardous materials spills. Heavy rains or winds could spread hazardous materials over a larger geographical area or create challenging cleanup conditions.

Challenging cleanup conditions could allow for the extent of contamination to grow. Additionally, natural hazards such as wildfires or earthquakes could cause hazardous materials releases as a secondary impact, requiring immediate response.

Facilities providing energy to the City may be impacted and cause secondary hazardous effects to the City. The battery storage facility, the Condor Energy Storage Project, holds up to 400 megawatts worth of energy when power from solar or wind is in abundance, then discharges the stored energy to the local electrical grid during times of peak energy demand.68 This facility may have risks such as power outages, environmental contamination, fire hazards, and access issues during a natural disaster. Additionally, the Highgrove Substation (ID SS2381) and Vista (ID SS1638) may also be impacted causing secondary hazards after a disaster.

The Comprehensive Environmental Response, Compensations, and Liability Act (CERCLA), Emergency Planning and Community Right-to-Know Act (EPCRA), and Washington State law require responsible parties to report hazardous materials releases if certain criteria are met. All hazardous materials releases exceeding reportable quantities must be reported to the National Response Center. As shown in Table 4-14, there have been a few hazardous materials incidents within the City in recent history. Most historical hazardous materials releases in Grand Terrace have been small in scale and impacts.

However, there are two Superfund sites just outside of the City in the neighboring cities of San Bernardino and Rialto; a Superfund site is a location that has been contaminated by hazardous waste or other toxins, posing a threat to both the environment and human health. Superfund is a government funded environmental program to address hazardous waste sites. The two Superfund sites near the City are listed below:
• The Norton Air Force Base (Landfill #2) Superfund Site is located in the southeastern corner of the City next to the San Bernardino International Airport. Past hazardous material management practices at the site contaminated groundwater and soil with polychlorinated biphenyls (PCBs), dioxins, heavy metals (such as lead) and acids. Following construction of the site’s remedy, operation and maintenance activities and monitoring are ongoing.69 • A Rockets, Fireworks, and Flares Superfund site is located in northwestern Rialto near Alec Fergusson Park. The "Rockets, Fireworks, and Flares" (RFF) site includes a 160- acre industrial area in Rialto, California where volatile organic compounds (VOCs) and perchlorate have contaminated soil and groundwater. The site, formerly known as the B.F. 68 San Bernardino Sun, Renewable energy storage project launches in Grand Terrace, https://www.sbsun.com/2024/08/05/renewable-energy-storage-project-launches-in-grand-terrace/, published August 5, 2024, accessed February 3, 2025.
69 EPA, NORTON AIR FORCE BASE (LNDFLL #2), https://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id=0902760, accessed August 22, 2024.

Goodrich site, also includes a six-mile-long area of groundwater contamination downgradient of the 160-acre area. Site investigations and cleanup are ongoing.

Hazardous materials spills along transportation corridors have not commonly been reported within the City of Grand Terrace in recent history. A review of the Pipeline and Hazardous Materials Safety Administration (PHMSA) incident reporting database showed the following hazardous materials incidents along transportation corridors since 1991.

No federally declared or state declared disasters relating to hazardous materials release/spills have impacted the planning area within the last five years; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area.

Table 4-14
Department of Transportation Hazardous Materials Spills in Grand Terrace Incident Route Incident City Date of
Incident
Quantity
Released
(LGA)*
Commodity Long Name
538 of Alhambra
Sub
Colton 9/9/2017 1,000 LGA Sulfuric acid with more than 51 percent acid
2359 South
Riverside Ave
Colton 11/20/2022 400 LGA Gasoline includes gasoline
mixed with ethyl alcohol, with
not more than 10% alcohol
Milepost: 537.20 Grand
Terrace
3/26/2006 0 LGA Liquefied Petroleum Gas
*LGA = Liquid gallons
Source: United States Department of Transportation: Pipeline and Hazardous Materials Safety Administration, Incident Statistics,
https://portal.phmsa.dot.gov/analytics/saw.dll?Portalpages&PortalPath=%2Fshared%2FPublic%20Website%20Pa ges%2F_portal%2FHazmat%20Incident%20Report%20Search, accessed August 22, 2024.

Hazardous materials will continue to be manufactured, used, stored, and transported throughout Grand Terrace, posing a risk of hazardous materials spills. Hazardous materials used for daily commercial and household operations rarely result in significant hazardous materials releases.

Additionally, Grand Terrace maintains a household hazardous waste collection program to reduce the potential for hazardous material incidents within the City.

Incidents caused by a traffic accident along hazardous materials transportation corridors including I-215 and the railroad along the western edge of the City pose a higher risk of hazardous materials spills. Furthermore, increased development trends may lead to increased manufacturing, use, and transportation of hazardous materials and a potentially higher incidence of traffic accidents involving hazardous materials. The use, production, and transportation of fuels and fuel products throughout the City also create the potential risk of hazardous materials spills. Gas stations and other industrial facilities will continue to use, store, and transport hazardous materials in the future.

Given the prevalence of facilities storing hazardous materials throughout Grand Terrace and previous occurrences, it has been determined that the probability of future hazardous materials events impacting the planning area is considered likely. A likely probability means between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. The LHMP planning team assigned a medium hazard planning consideration to the hazards and

impacts associated with hazardous materials events based upon a likely probability and moderate impacts of future events.

Climate change poses an indirect risk related to hazardous materials release. According to the U.S. Environmental Protection Agency (EPA), climate change may increase exposure to chemicals. More frequent and intense storms may increase the likelihood of flooding, causing chemicals held in underground storage tanks, landfills, and storm debris to leak or spread to previously unsoiled areas.70 Further, hazardous materials releases during wildfire or severe weather events could spread contamination to large geographic areas and amplify long-term impacts to human and ecological health. Spills or releases in challenging clean-up conditions can result in more severe damage or impacts compared to spills during normal conditions.

Hazardous material releases have the potential to affect the entire planning area, and therefore all critical facilities within the City are considered vulnerable. Impacts from hazardous materials spills can vary significantly based on the type, content, and quantity of hazardous materials released, and the release location. The threat of a major hazardous material incident in Grand Terrace could be derived from either transportation, utilities, industrial/agricultural sources, clandestine operations and/or illegal camping. Major highways including Interstate 215 and the railroad tracks in the western region of the City run through the planning area, however the likelihood of a significant quantity of hazardous materials being routinely transported is low.

Although hazardous materials incidents could result in damage to City infrastructure, the most significant impact is the potential human health hazards as a result of a spill or potential environmental contamination. Environmental contamination could impact air and water quality and could involve costly long-term clean-up measures. Damage to utility systems could disrupt service or cause significant outages. The intent behind hazardous materials spills can influence the magnitude of impact as well. An intentional hazardous materials release linked to terrorism or sabotage attempts could have wider-ranging impacts compared to an unintentional release. Thus, the threat of harm and injury is highly dependent on the actual incident.

The San Bernardino County Fire District supports the California Environmental Reporting System (CERS) to report, collect, and manage data related to hazardous materials.71 Future incidents involving hazardous materials within the City of Grand Terrace will ultimately be captured through the CERS reporting system.

Changes in Vulnerability
Changes in land use, development, and population since the previous LHMP indicate past changes in hazard vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development for a description of past and future growth within Grand Terrace.

To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth and has initiated various capital improvement projects. Changes in land use and capital 70 United States Environmental Protection Agency, Climate Adaptation – Chemical Exposure and Health, https://www.epa.gov/arcx/climate-adaptation-chemical-exposure-and-health, published June 21, 2023, accessed April 15, 2024. 71 SBC Fire, About CERS, https://sbcfire.org/hmcers/, accessed August 22, 2024.

improvement projects have enabled residential development and population growth within the planning area. Based on population changes and development trends, it is reasonable to assume that vulnerability to hazardous materials has increased due to additional population and density in the planning area since the 2017 LHMP.

Anticipated development and capital improvements in the next five years will enable more population growth and increased density within Grand Terrace into the future. Population and residential development are anticipated to increase in accordance with the California Department of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates an additional 630 housing units in the City of Grand Terrace between 2021 and 2029.

Incidents involving hazardous materials have the potential to impact the entire City of Grand Terrace. The City anticipates continued growth and development in residential and non-residential areas over the 5-year planning horizon of this LHMP which would also be vulnerable to incidents involving hazardous materials. Population and density increases would increase the number of people at risk of the hazardous materials hazard. Considering the potential for population growth, additional residential development, increased density and anticipated capital improvement projects throughout the City, it is reasonable to assume that vulnerability to hazardous materials will increase over the planning horizon of this LHMP.

Section 3.6, Socially Vulnerable Populations and Determination, includes a detailed determination of socially vulnerable populations (SVP) within the planning and the characteristics that make those populations more vulnerable to hazards. The hazardous materials hazard would apply to the entirety of the planning area, including Socially Vulnerable Populations (SVPs) within Grand Terrace and other high-risk individuals located throughout the planning area, but particularly those located in northeastern areas of the City. Census tracts with high vulnerability due to high SVIs scores and proximity of industrial areas are tracts 40.04, 71.07, 71.09, and 71.06.

Incidents involving hazardous materials, including transportation accidents involving hazardous materials, may disproportionately impact SVPs by exposing them to toxic chemicals, which can cause serious health issues such as respiratory problems, skin irritation, and long-term illnesses.

SVPs such as low-income households in the planning area often have limited resources to respond to and recover from such incidents and may face barriers in accessing timely information and emergency services. Additionally, the displacement caused by spills can be particularly challenging for those with mobility issues, financial constraints, or lack of local knowledge, further exacerbating their vulnerability. Homeless populations may also struggle to obtain access to medical care if they face health impacts due to a hazardous materials spill.

Pandemic
Disease (Infectious/Vector-Borne)
Infectious diseases are caused by undesirable organisms (insects, bacteria, viruses, etc.), resulting in health impacts, symptoms and/or serious harm to plants, animals, or humans. These organisms threaten human health by infecting people with disease, some of which are potentially fatal. Vector-borne diseases are a type of infectious disease which the World Health Organization (WHO) defines as human illnesses caused by parasites, viruses, and bacteria that are only transmitted by vectors. In this context, vectors are “living organisms that can transmit infectious pathogens between humans, or from animals to humans”.72 Communicable disease is an umbrella term for infectious diseases that are spread from one person to another through contaminated surfaces, bodily fluids, and through the air. In any case, infectious diseases transmitted from vector-to-person or person-to-person may have significant health impacts and symptoms that affect the structure or function of the immune, neurological, or other physiological system of the human body. In many cases, infectious diseases have severe health impacts up to and including death.

Specific vectors of concern in the City of Grand Terrace include mosquitos, ticks, rodents, and other animals. These vectors are known carriers of hantavirus, rabies, West Nile Virus (WNV), and tick-borne diseases such as Lyme disease.

Pandemic
The Centers for Disease Control and Prevention (CDC) defines an epidemic as an increase, often sudden, in the number of cases of a disease above what is normally expected in a population.

The CDC makes the distinction that a pandemic refers to an epidemic that has spread over several countries or continents, usually affecting signification proportions of the population.73 This definition of pandemic refers specifically to infectious diseases that have spread over or impacted large geographic areas. Non-infectious diseases, such as asthma or diabetes, may exist in “pandemic proportions” but do not readily spread throughout a population and thus do not constitute a pandemic. Pandemics also exclude vector-borne diseases, categorized by transmission through a vector (rats, mosquitos, etc.).

Pandemics require two components: 1) an agent (disease or virus) and 2) a susceptible host population. The host population, usually humans, is the primary mode by which agents are spread under this definition of pandemic. Pandemic agents are spread from person to person through direct or indirect contact, so humans are understood to be the causal element of pandemics.

Airborne diseases and those spread through physical contact pose higher risks to the community because they are difficult to isolate and control. Diseases such as influenza, pertussis, 72 World Health Organization, Vector-Borne Diseases, https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases, accessed September 19, 2024.
73 CDC, Lesson 1: Introduction to Epidemiology, Section 11, https://archive.cdc.gov/#/details?url=https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html, accessed September 19, 2024.

tuberculosis, and meningitis are spread by these pathways and therefore have the potential to reach pandemic levels.

Viruses of special concern in pandemics are novel viruses, which are new viral strains not previously identified in humans. Novel viruses present public health challenges as limited information about transmission, prevention, and treatment is available. Further, the human body does not have natural immune defenses prepared to fight novel viruses.74 In recent history, novel viruses originated as zoonotic diseases; the virus beginning in animals evolves to transfer from human to human. Examples of zoonotic diseases becoming human pandemics include Covid-19 (theorized to originate in bats), H1N1 influenza (originated in pigs), and H5N1 influenza (originated in birds).75
Active Shooter
An active shooter is defined by the FBI as an individual actively engaged in killing or attempting to kill people in a populated area. Active shooters select victims at random, and the shooting event is unpredictable and often evolves quickly.76 Active shooters select public gathering and community areas, often targeting schools, places of worship, and transportation centers. There may be one or more shooters involved in an event, and there is not one demographic profile of an active shooter. The FBI identify the pathway to active shooting as typically involving an unresolved real or perceived grievance and an ideation of a violent resolution.77 Active shooter and terrorist incidents can both result in mass casualties, where emergency response and resources are overwhelmed by the number or severity of casualties.

Power Outage, Public Safety Power Shut-Off
Power outages are a major secondary effect of severe weather events in the City. An outage could result in damaged power equipment or equipment failures and can affect multiple jurisdictions for hours. This type of event can range from a moderate event to a catastrophic regional event that may threaten human life, safety, and health, or interferences with vital services.

During severe weather incidents such as high winds, extreme heat, or severe flooding, Southern California Edison (SCE) may implement an operational practice called Public Safety Power Shutoffs (PSPS) to preemptively shut off power in high-risk areas during potentially dangerous conditions. This program is designed to proactively prevent SCE facilities from starting a wildfire in at risk areas when winds and temperatures are high.

Strong Santa Ana winds, high temperatures, and low humidity are all severe weather conditions that could trigger a PSPS event. It is possible for extreme weather incidents outside of the City to trigger a PSPS that affects the service area (i.e., strong winds affecting regional infrastructure 74 GoodRX Health, The Novel Coronavirus: What are Novel Viruses, and How do they Impact Public Health?, https://www.goodrx.com/conditions/covid-19/what-does-novel-coronavirus-mean-science-medical-definition, updated February 21, 2023, accessed September 19, 2024.
75 CDC, Lesson 1: Introduction to Epidemiology, Section 11, https://archive.cdc.gov/#/details?url=https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html, accessed September 19, 2024.
76 Federal Bureau of Investigation, OPS Active Shooter Guide, https://www.fbi.gov/file-repository/active-shooter-508.pdf/view, accessed September 19, 2024.
77 Federal Bureau of Investigation, Addressing the Problem of the Active Shooter, https://leb.fbi.gov/articles/featuredarticles/addressing-the-problem-of-the-active-shooter, published May 7, 2013, accessed September 19, 2024.

that powers SCE grids in San Bernardino County). The frequency of these events depends on the weather and environmental factors, and SCE makes decisions based on internal threat thresholds, assessment of real-time information, and situational awareness data. When possible, SCE intends to notify customers prior to a PSPS event. When weather forecasts indicate extreme fire conditions, SCE begins predictive modeling to assess the potential impacts while monitoring weather watch alerts from the National Weather Service. Three days prior to the forecasted PSPS, SCE would coordinate first with local governments, the emergency management community, first responders, and other critical infrastructure/service providers. Two days prior to the forecasted PSPS, notices would go out to SCE customers with a follow-up one day before a notice of power shut off. It is noted that actual or sudden onset of extreme weather conditions could impact the intended coordination and notification efforts.78 Outside of the PSPS events, there is the potential for unplanned power outages to occur within the City of Grand Terrace. SCE defines a major outage as a large, unexpected outage caused by either accidents or natural disasters. While uncommon, loss of electrical power is a potential secondary effect of heavy rains or strong winds. Other types of events that could occur is mechanical power failure due to aging equipment.

Train Derailment
Train derailment poses as a significant hazard to the City of Grand Terrace. This hazard can lead to injuries or fatalities for passenger, crew and nearby individuals or wildlife. Train derailment can also cause significant environmental damage if the train is carrying hazardous material, which can release toxic substances in the air, soil, and water. Release of toxic substances can lead to long-term environmental contamination and health risks for human and wildlife.

Train derailment can occur to either passenger/commuter trains or freight trains. Passenger and commuter trains carry people, while freight trains carry goods, raw resources such as coal, lumber, ore, and toxic substances. Train derailment can occur due to broken or misaligned rails, mechanical failures of the train itself, and operational errors such as excessive speed especially around curves or improper handing by the train operator. Collisions between two or more trains, infrastructure, crossing vehicles, or debris can also derail a train causing collateral damage to individuals and properties near the incident.79 Weather conditions such as heavy rain, strong winds, flooding, or landslides can misalign tracks and cause derailments. During extreme heat weather conditions, steel rails will expand causing a train to buckle. The cost of train derailment can range up millions of dollars with property damages, economic loss, health impacts, environmental cleanups, and legal fees.80
Pandemic
Disease (Infectious/Vector-Borne)
A public health crisis involving vector-borne diseases can originate within the City or neighboring communities before spreading into and throughout the planning area. Vector-borne diseases and 78 Southern California Edison, Public Safety Power Shutoff, https://www.sce.com/wildfire/psps, accessed September 19, 2024. 79 International Railway Safety Council, Railway Safety, https://international-railway-safety-council.com/common-risks-managedrailway-industry/, accessed September 12, 2024. 80 Fast Company, $600 million will go to Ohio residents affected by the Norfolk Southern derailment, https://www.fastcompany.com/91198017/600-million-ohio-residents-affected-norfolk-southern-derailment, published September 26, 2024, accessed September 26, 2024.

pests could potentially impact any areas throughout the City of Grand Terrace or San Bernardino County. Outdoor spaces are most likely to be areas of vector congregation, but specific vectors prefer different environments. Vectors such as rats may thrive in unmaintained structures or other areas with trash and food sources. Mosquitos require standing water to reproduce, prefer warmer environments, and may be found throughout the planning area. Ticks and rodents may interact with humans anywhere throughout the planning area, although outdoor and wildland areas may pose a higher risk of contact.

The magnitude and severity of vector-borne diseases rely on many factors such as the range and distribution of the vector population. A crisis can occur if dense populations of vectors carrying disease encounter large groups of people. Vector-borne disease could spread quickly among residents in urban areas, including vulnerable populations such as elderly persons, low-income populations, and people living in overcrowded housing conditions. The severity of impacts from vector-borne diseases are highly variable; some diseases may have relatively minor health impacts while others could be deadly. A worst-case scenario would be a vast vector population that transmits a disease with an extremely high mortality rate. In this scenario, impacts would be severe and could extend throughout populations within the City of Grand Terrace.

Pandemic
By definition, a pandemic is understood to have a significant geographic range with impacts on a global scale. Effects of a pandemic would impact the entirety of the planning area, depending on the disease and susceptible population. Pandemic diseases have been known to spread quickly throughout communities. Many diseases spread through close contact, meaning that highly populated areas are more prone to widespread outbreaks; many public activities are centered out of City Hall, Grand Terrace Senior Center, Richard Rollins Community Park, and local schools making this area more likely to experience the spread of pandemic disease. Indoor areas where people are in close contact with each other appear to be significant vectors for diseases that are spread through respiratory droplets.81 Areas with relatively low population densities throughout the planning area are less likely to experience a widespread outbreak. While the entirety of the City would be at risk, specific subsets of the population may be more susceptible than others, including vulnerable populations such as the very young (those under 1 year), elderly, and immuno-compromised individuals, depending on the disease.82, 83 The extent to which a pandemic could impact the City of Grand Terrace depends on the disease type and symptoms. Some diseases may be highly transmissible and affect a significant portion of the population but may carry minor symptoms. On the other hand, a disease might be very deadly but not be easily transmitted. The worst-case pandemic scenario is a disease that is both highly transmissible and carries a high mortality rate. The severity and extent of a pandemic may also depend on the ability to respond by developing and administering vaccinations, or other public health measures for mitigating the spread of the disease. The pandemic hazard, including infectious and vector-borne disease, does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area.
81 California Department of Public Health, Isolation Q&A, https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Covid-19/IsolationQA.aspx, accessed September 19, 2024. 82 Mayo Clinic, Covid-19 in babies and children, https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/coronavirus-inbabies-and-children/art-20484405, published October 21, 2022, accessed September 19, 2024. 83 University of Michigan, Which Populations are Most Vulnerable to the Coronavirus Pandemic?, https://sph.umich.edu/news/2020posts/which-populations-are-most-vulnerable-to-coronavirus.html, published April 6, 2020, accessed September 19, 2024.

Active Shooter
The specific location of terrorism and active shooter incidents are difficult to predict. Generally, locations most vulnerable to terrorism and active shooters are places where people gather, places of political importance, infrastructure, and destinations. Examples include but are not limited to:
• Schools
• Hospitals
• Churches/religious centers
• Employment centers
• City Hall/County Seat
• Community centers
• Libraries
• Transit operations and stops
• Shopping malls/large retail centers
• Highways and other transportation infrastructure
• Power plants and utility infrastructure
• Event/entertainment centers
The City of Grand Terrace, located in San Bernardino County, includes land uses pertaining to this list such as parks, commercial buildings, residence, manufacturing, and transportation. The active shooter hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area.

The severity of impacts of active shooter are difficult to predict and would depend on the nature of the attack and target. The impacts vary in size and severity depending on the specific event, but typically results in loss of life, psychosocial damage, and service/industry disruptions. The effects of psychosocial damage, and service/industry disruptions would likely be experienced by the entire community in the event of an active shooter. Further, the City could experience secondary effects due to terrorism incidents located outside of the City. The City of Grand Terrace is surrounded by the City of Colton, the City of Riverside, and unincorporated areas of Riverside County, and is in close proximity to major urbanized areas. The highly populated and developed nature of the City of Grand Terrace and surrounding areas present a potential target for active shooting. Depending on the type and size of an attack in a neighboring jurisdiction, impacts could extend to the City.

Power Outage, Public Safety Power Shut-Off
SCE designates High Fire Risk Areas as areas with circuits within California Public Utilities Commission’s (CPUC) Tier 2 (elevated risk) and Tier 3 (extreme risk) Fire Threat Areas. The CPUC Fire-Threat Map was developed with input from the U.S. Forest Service, California Department of Forestry and Fire Protection, and the State’s investor-owned utilities, including SCE. SCE uses their own thresholds prior to initiating a PSPS event. When evaluating weather and environmental conditions, SCE considers a variety of factors which include but are not limited to:
• National Weather Service Red Flag Warnings;
• SCE meteorological assessments;
• SCE Fire Potential Index;

• SCE Fire Scientist assessments;
• Real-time situational awareness information;
• SCE Fire Management/Office of Emergency Management input; • Concerns from local or State fire authorities;
• Mandatory or voluntary evacuation orders in place;
• Expected impact of de-energizing circuits on essential services (including public safety agencies, water pumps, traffic controls, etc.); and
• Other operational considerations to minimize wildfire ignitions.

Figure 4-8
CPUC Fire-Threat Map
Source: CPUC, High Fire Threat District (HFTD),
https://www.arcgis.com/apps/webappviewer/index.html?id=5bdb921d747a46929d9f00dbdb6d0fa2, accessed December 17, 2024.

Note: Blue circle indicates the approximate location of the City of Grand Terrace

The magnitude or extent of impacts to the City would depend on the duration of the outage and the size of the impacted area. Prolonged or widescale power shutoffs across the City or Inland Empire region could significantly disrupt City operations and emergency response. The power outage and PSPS hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area.

Train Derailment
There are two major freight railroad services that run near the City of Grand Terrace: the Union Pacific Railway and the BNSF Railway. The Union Pacific is a freight service that ships food, forests products, automobiles agricultural products, coal, and chemicals. The Union Pacific has a stop in the City of Colton, located north of the City of Grand Terrace. The BNSF Railway is a major freight railroad network in California and the greater U.S. region. Both freight trains use tracks near Grand Terrace High School, transecting the western portion of the City from north to south.

Figure 4-9
Railway Routes in Grand Terrace
Source: CN, Network Map, https://cnebusiness.geomapguide.ca/, accessed December 18, 2024.

Although the City of Grand Terrace does not have a commuter rail train stop, two commuter rail systems, the Metrolink and the Amtrak, use tracks in the western portion of the City of Grand Terrace. The railway services use tracks intersecting Main Street and adjacent to Grand Terrace High School. All train services use the Burlington Northern and Santa Fe Railroad and Southern Pacific Railroad which traverse the western portion of the City of Grand Terrace from north to south, Figure 4-10, Railroads in the City of Grand Terrace. The train derailment hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area.

Figure 4-10
Railroads in the City of Grand Terrace
Source: BSNF Railway, BSNF Map California, https://bnsfcalifornia.com/wp-content/uploads/2018/01/BNSFCA-MapCalifornia-Full.png, accessed September 19, 2024.

Pandemic
In 2020, the Covid-19 pandemic began in Wuhan, China before becoming a global pandemic that would infect over 775 million people and claim the lives of over 7 million.84 The entire population of the City of Grand Terrace was impacted by this event, and the City was included in the federal disaster declaration issued for this hazard event by FEMA.

The City of Grand Terrace experienced significant impacts from the Covid-19 Pandemic. A novel coronavirus disease, namely SARS-CoV-2 or Covid-19, was identified in Wuhan, China in December 2019. By March 2020, Governor Gavin Newsom issued a statewide stay-at-home order, prohibiting all people in the State of California from leaving their homes apart from essential services and limiting the operations of non-essential businesses.

At the time of this document was prepared, 8,144 known deaths in San Bernardino County have been attributed to Covid-19.85 As part of the response to slow the spread of the virus, nonessential businesses and schools were closed or transitioned to remote environments, when feasible. A significant milestone and improvement against the pandemic came in December of 2020 with the release of the Covid-19 vaccine. The City of Grand Terrace and San Bernardino County made various resources available based on guidance from the WHO, CDC, and California Department of Public Health (CDPH). Mask mandates were issued for indoor spaces, and proof of vaccination requirements were established for certain activities to help stop transmission.

Generally, the pandemic resulted in significant economic and public health impacts that are still reverberating throughout the City. At the time of this writing, Covid-19 is a seasonally recurring issue as vaccines, masks, and social distancing has made disease transmission and treatment much more manageable.

Before Covid-19, the most recent pandemic occurred in 2009: the (H1N1) pdm09, “swine flu” pandemic.86 H1N1pdm09 primarily affected children and young/middle-aged adults, atypical from most influenza pandemics. Between April 2009 and April 2010, the CDC estimates over 60 million cases, nearly 275,000 hospitalizations, and over 12,000 deaths affected the United States population. The World Health Organization declared an end to the global pandemic in August 2010; however, the virus continues to circulate as a seasonal influenza virus.87 Both the 1968 and 1918 pandemics were caused by avian flu outbreaks. The 1968 pandemic was caused by an influenza H3N2 virus, with an estimated death toll of 116,000 in the United States and an estimated worldwide toll of 1.1 million.88 Medical advances in the 1960s including antiviral medications and expanded influenza vaccine options significantly helped to combat this pandemic. The 1918 pandemic was an outbreak of influenza caused by an H1N1 virus. The virus spread worldwide from 1918-1919. It is estimated that one third of the worldwide population at 84 World Health Organization, WHO Covid-19 Dashboard, https://data.who.int/dashboards/Covid19/deaths?n=o, accessed September 19, 2024.
85 USA Facts, San Bernardino County, California coronavirus cases and deaths, https://usafacts.org/visualizations/coronaviruscovid-19-spread-map/state/california/county/san-bernardino-county/, accessed September 19, 2024. 86 CDC, About Human Infections with Variant Influenza Viruses, https://www.cdc.gov/swine-flu/variant-flu-in-humans/index.html, published June 27, 2024, accessed September 19, 2024.
87 CDC, 2009 H1N1 Pandemic (H1N1pdm09 virus), https://archive.cdc.gov/www_cdc_gov/flu/pandemic-resources/2009-h1n1- pandemic.html, last reviewed June 11, 2019, accessed September 19, 2024. 88 CDC, Learning from Pandemic Flu, https://www.cdc.gov/museum/pdf/cdcm-pha-stem-learning-from-pandemic-flu-lesson.pdf, accessed September 19, 2024.

the time, about 500 million people, became infected with the virus. The pandemic resulted in an estimated 675,000 deaths in the United States alone and over 50 million deaths worldwide.89 One state declared disaster for the pandemic hazard has impacted the planning area within the last five years:
• State of Emergency: Covid-19 Pandemic – March 4, 2020 One federally declared disaster for the pandemic hazard has impacted the planning area within the last five years; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area.
• DR-4482-CA: Covid-19 Pandemic – March 22, 2020
Active Shooter
On New Year’s Eve of 2015, a shooting occurred outside of the Cal Skate Roller Rink killing one person and injuring two people. Five people involved with the shooting were arrested. 90 Regionally
in San Bernardino County, a terrorist attack occurred in 2015 with 14 people killed and 24 people wounded including two police officers.91
Public Safety Power Shutoff (PSPS)
PSPS events often target wildland areas with high wildfire risk, but they can impact a much wider region. The targeted area is the area at risk due to weather conditions, especially during severe storm events in the planning area. Given the long, connected nature of power supply systems, a shutoff event targeted to a small at-risk zone can affect power to larger areas beyond.

SCE designates High Fire Risk Areas as areas with circuits within California Public Utilities Commission’s (CPUC) Tier 2 (elevated risk) and Tier 3 (extreme risk) Fire Threat Areas. The CPUC Fire-Threat Map was developed with input from the U.S. Forest Service, California Department of Forestry and Fire Protection, and the State’s investor-owned utilities, including SCE. SCE uses their own thresholds prior to initiating a PSPS event. When evaluating weather and environmental conditions, SCE considers a variety of factors which include but are not limited to:
• National Weather Service Red Flag Warnings
• SCE meteorological assessments
• SCE Fire Potential Index
• SCE Fire Scientist assessments
• Real-time situational awareness information
• SCE Fire Management/Office of Emergency Management input • Concerns from local or State fire authorities
• Mandatory or voluntary evacuation orders in place
89 Ibid.
90 ABC 7, 5 arrested for Grand Terrace NYE shooting, https://abc7.com/grand-terrace-shooting-murder-new-years-eve-nye/463860/, published January 6, 2015, accessed October 3, 2024.
91 PBS News, Everything we know about the San Bernardino shooting, https://www.pbs.org/newshour/nation/everything-we-knowabout-the-san-bernardino-shooting, published December 3, 2015, accessed September 19, 2024.

• Expected impact of de-energizing circuits on essential services (including public safety agencies, water pumps, traffic controls, etc.)
• Other operational considerations to minimize wildfire ignitions.

In November 2024, the City experienced a 36-hour PSPS implemented by Southern California Edison.92 This event was triggered by high winds, low humidity, and dry vegetation and was designated to prevent wildfires caused by electrical equipment.

In late January 2025, the City experienced approximately 11 days of power outages due to fire conditions that disrupted City operations.9394 Traffic signals at Honey Hill and Barton Road were non-operational during the outage, and the City offered public messaging to residents to identify locations where chagrining stations, Wi-Fi, snacks, and water were available.95 Train Derailment
Although there have been no occurrences of train derailment within the planning area, there is a possibility that train derailment can occur in the future. More than 4,000 trains have derailed since 2020 with nearly 70 percent occurring in urban areas like the City of Grand Terrace.96 Within San Bernardino County, there have been several incidents of train derailment, with none occurring in the City.97 Several train derailment incidents occurred adjacent to the City of Grand Terrace in the Colton and Bloomington areas within the past ten years. These incidents occurred due to varying reasons such as brake valve malfunction, automatic block, other mechanical and electrical failures, and interaction of lateral/vertical forces.98 Pandemic
The likelihood of pandemics has increased over the last hundred years due to increased globalization, urbanization, and changes in land use. Another potential key contributor to an increased likelihood of pandemics is factory farming. The shift from small scale animal agriculture to large factory farming operations may be a driving factor in recent pandemic diseases and may cause the next pandemic. For these reasons, the probability of future occurrences is considered likely. A likely probability means between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. However, the exact time and location that another virus with the potential to create a global pandemic would occur is difficult to predict. Future pandemic occurrences would likely result from a mutation of a virus that results in a new virus to which the population has no immunity. With medical technology, it is possible to anticipate new viruses and 92 City News Groups, Inc., Power Outage Grand Terrace, https://www.citynewsgroup.com/articles/power-outage-grand-terrace, published November 20, 2024, accessed December 6, 2024. 93 Instagram Grand Terrace Chamber of Commerce, Power Outage Grand Terrace, https://www.instagram.com/grandterrace_chamberofcommerce/reel/DEsvgKzyey9/, posted January 11, 2025, accessed February 27, 2025.
94 City of Grand Terrace, Power Outage Announcement, https://www.grandterraceca.gov/residents/news_information/what_s_new/power_outage_announcement-_jan_22__2025, accessed February 26, 2025. 95 City of Grand Terrace, Power Outage Announcement, https://www.grandterraceca.gov/cms/one.aspx?portalId=12337339&pageId=20666120, accessed February 26, 2025. 96 NLC, Rail Safety in Communities Across the U.S., https://www.nlc.org/resource/interactive-rail-safety-map-see-derailments-incommunities-across-the-u-s/, published June 1, 2023, accessed September 26, 2024. 97 Ibid.
98 Ibid.

develop vaccines to prepare for the next outbreak; however, entirely preventing a pandemic through preemptive measures is unlikely.

Active Shooter
The Planning Team has determined that active shooter has a likely probability of occurring within the planning area. A likely probability means between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with active shooter events based upon a likely probability and moderate impacts of future events.

The risk for the City of Grand Terrace is heightened due to the presence of multiple City/County governmental buildings, along with presence of schools, churches, and other critical assets.

Additionally, terrorism and active shooter threats are not necessarily determined by the incidence of previous occurrences and are difficult to predict. Because of the dynamic nature of terrorist threats, terrorism can occur without much warning and may occur in any area within the City.

Power Outage, Public Safety Power Shut-Off
Based on previous occurrences, there is a likely probability of future PSPS events in the future.

A likely probability means between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with PSPS events based upon a likely probability and moderate impacts of future events.

Train Derailment
Based on previous occurrences, the likelihood of future train derailment events affecting the City is considered likely. A likely probability means between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with train derailment events based upon a likely probability and moderate impacts of future events.

Pandemic
While pandemics typically originate for reasons outside of climate change, it is possible that the impacts of climate change will make pandemics more severe. According to the National Science Foundation, climate change will likely require humans to relocate and wild animals to find new habitats, dramatically increasing the risk of viral jumps/transmissions. For example, rising temperatures are expected to have a major impact on bats – a species known for novel virus sharing, most recently with Covid-19 or the Ebola virus.99 Furthermore, according to the Harvard T.H. Chan School of Public Health, increases in climate change and development such as rising temperatures and deforestation for agricultural purposes contribute to habitat loss worldwide.100 Consequently, the loss of habitat forces animals to migrate and potentially face additional contact with other animals and humans, increasing the risk of disease transmission. When coupled with 99 National Science Foundation, Study finds that climate change could spark the next pandemic, https://beta.nsf.gov/news/study-findsclimate-change-could-spark-next, published May 25, 2022, accessed September 19, 2024. 100 Harvard T.H. Chan School of Public Health, Coronavirus and Climate Change, https://www.hsph.harvard.edu/cchange/subtopics/coronavirus-and-climate-change, accessed September 19, 2024.

increased urbanization and globalization, pandemics could continue to spread as quickly or more quickly than the Covid-19 pandemic. While the full effects of climate change on pandemics are not fully known, it is reasonable to assume the risk for future pandemics continues to exist.

Active-Shooter
As terrorism and active shooter events are human-caused, these hazards are not directly tied to climate change impacts. However, prolonged climate change impacts can cause conflicts regarding natural resources and livelihood insecurity, as well as food insecurity or water scarcity.

Terrorist organizations could operate more easily in fragile and conflict-affected environments, according to the Climate Diplomacy Organization.101 However, terrorism and active shooter threats are generally considered to be independent from climate change.

Power Outage, Public Safety Power Shut-Off
As the effects of climate change continue to be observed, PSPS events are expected to increase as hazard events continue to be exasperated due to the effects of climate change. In recent years, PSPS events have been increasingly utilized in California as climate change, wildfire fuel accumulation, and expanded development of fire-prone lands increase the risk of wildfire events.102 In the event of a severe storm event, a PSPS may be deployed if electrical infrastructure is damaged to reduce the risk of damage to life and property within the City. An example of this would be high winds causing downed power lines that threaten the safety of local residents.

Train Derailment
Climate change can impact the stability and safety of railroads that can increase the risk of train derailment. Conditions such as extreme heat, extreme cold, flooding, and drought can increase the chances of train derailment. In extreme heat conditions, high temperatures can cause the metal in rail to expand and buckle causing sun kinks which misalign tracks and derail trains.103,104 Flooding from heavy rains can erode the ground beneath tracks, destabilizing them allowing for tracks to slip.105 Prolonged dry conditions such as drought can dry out the soil, leading to subsidence and sinking also misaligning tracks.106
Human-caused hazards have the potential to affect the entire City of Grand Terrace. Thus, all City critical facilities, infrastructure systems, structures, residents, and businesses are considered 101 Climate Diplomacy Organization, Insurgency, Terrorism and Organized Crime in a Warming Climate, https://www.climatediplomacy.org/publications/insurgency-terrorism-and-organised-crime-warming-climate, accessed September 19, 2024. 102 Wong-Parodi, Gabrielle, Support for public safety power shutoffs in California: Wildfire-related perceived exposure and negative outcomes, prior and current health, risk appraisal and worry, https://www.sciencedirect.com/science/article/abs/pii/S2214629622000032#:~:text=In%20recent%20years%2C%20Public%20Safet y,development%20in%20fire%20prone%20lands., accessed September 19, 2024. 103 U.S. Department of Transportation Federal Railroad Administration, FRA’s Climate and Sustainability Program, https://railroads.dot.gov/rail-network-development/environment/fras-climate-and-sustainabilityprogram#:~:text=Threats%20from%20climate%20change%20include,infrastructure%20near%20rivers%20and%20valleys, updated September 19, 2024, accessed September 19, 2024.
104 Climate Central, Derailments May Increase as ‘Sun Kinks’ Buckle Tracks, https://www.climatecentral.org/news/climate-changewarp-railroad-tracks-sun-kinks-17470, accessed September 19, 2024. 105 Inside Climate News, Climate Change Poses a Huge Threat to Railroads. Environmental Engineers Have Ideas for How to Combat That, https://insideclimatenews.org/news/08042022/climate-change-railroads-adaptation/, published April 8, 2022, accessed September 19, 2024.
106 Rosetti, Michael, Potential Impacts of Climate Change on Railroads, https://www.transportation.gov/sites/dot.gov/files/docs/rossetti_CC_Impact_Railroads.pdf, accessed September 19, 2024.

vulnerable to human-caused hazards. The entire City population of 13,104 people and 4,973 occupied housing units are potentially vulnerable. The extent of harm or injury is highly dependent upon the nature of the actual incident. Active shooter and train derailment incidents could damage physical buildings and property or impact human health, and the effects of human-caused hazards could involve costly long-term clean-up actions and recovery measures. In the event of wildfire conditions and high winds, power outages due to a PSPS could impact the ability for local residents to use electrical devices and appliances including ovens, dishwashers, air conditioners, and devices with access to the internet.

Active shooter incidents may also occur anywhere within the City, and thus the entirety of the City is considered vulnerable. Active shooters specifically target people, and attacks usually occur at places or events where large numbers of people congregate. Schools, municipal facilities, or public utility and transportation infrastructure may also be targeted during an active shooter event.

Depending on the nature of the attack, impacts could be widespread throughout the planning area or highly localized. A train derailment incident could take place along the rail lines along the western border of the City, with the primary concern from this hazard being damage, injuries, and fatalities that can occur due to a collision or accident.

Physical structures are not typically vulnerable to pandemics; thus, a failure of a critical facility due to pandemic is unlikely. The main concern for pandemic vulnerability is the impact on human health, and critical facilities support in minimizing this impact. Health and medical community lifelines may be strained in response to a pandemic. Health impacts may be widespread throughout the City and impact a significant percentage of the population. Additionally, pandemics may result in significant economic impacts to the City, businesses, and residents. Depending on the size and scale of the disease outbreak, the City or other emergency responders may experience staffing challenges to continue services. Furthermore, areas with a higher population density have an increased risk of exposure or transmission of disease due to closer proximity to potentially infected people.

Changes to Vulnerability
Changes in land use, development, and population since the previous LHMP indicate past changes in hazard vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development for a description of past and future growth within Grand Terrace.

To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth and has initiated various capital improvement projects.

Changes in land use and capital improvement projects have enabled residential development and population growth within the planning area. Based on population changes and development trends, it is reasonable to assume that vulnerability to human-caused hazards has increased due to additional population and density since the 2017 LHMP.

Anticipated development and capital improvements in the next five years will enable more population growth and increased density within Grand Terrace into the future. Population and residential development are anticipated to increase in accordance with the California Department of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates an additional 630 housing units in the City of Grand Terrace between 2021 and 2029.

Human-caused hazards have the potential to impact the entire City of Grand Terrace. The City anticipates continued growth and development in residential and non-residential areas over the 5-year planning horizon of this LHMP which would also be vulnerable to human-caused hazards.

Population and density increases would increase the number of people at risk of human-caused hazards. Considering the potential for population growth, additional residential development, increased density, and anticipated capital improvement projects throughout the City, it is reasonable to assume that vulnerability to human-caused hazards will increase over the planning horizon of this LHMP.

The location, extent, and magnitude of human-caused hazards would apply to the entirety of the planning area, including SVPs and other high-risk individuals located within the City. No physical infrastructure or unique considerations elevate risk to specific human-caused hazards. The primary concern for SVPs and other high-risk individuals is outreach and communication.

Emergency communication and alerts in the case of human-caused hazards should consider cultural competence, including consideration for minority populations and individuals with limited English proficiency. Additionally, considerations for overcrowded households and persons living below the poverty line may be required as densely populated and overcrowded housing units put more individuals at risk to hazards, both physically and economically. SVPs in Grand Terrace are particularly concentrated in northeastern areas of the City. More specifically, census tracts 40.04,

71.07, and 71.06 may have more vulnerability to train derailment as the railroad tracks traverses these census tracts. Census tracts 40.04, 71.07, 71.09, and 71.06 may also be more vulnerable during a pandemic with limited access to resources.

Considerations for SVPs throughout the planning area were incorporated into the mitigation strategy in Section 5.0. Specifically, the LHMP Planning Team tailored Mitigation Action #31,to mitigate the socioeconomic impacts of human-caused hazards that may disproportionately impact SVPs in Grand Terrace.

Landslide is a generalized term for a falling mass of soil or rocks. When a hillside or slope becomes unstable, downslope movement of rock and soil occurs under the direct influence of gravity. Landslides are often sudden, although some occur very slowly over a long period of time.

Loose and fractured materials are more likely to slide than compact materials or solid rock, and steep slopes are at greater risk than gentle rises.

Landslides are usually induced by either earthquakes or saturated slopes. The shaking of an earthquake can decrease slope stability, or in a more severe instance, fracture the earth material enough that the material slides. Moisture-induced landslides can occur when the ground soaks up enough water that the soil becomes loose and unstable. This is often the result of intense or long-lasting rainfall, but can also result from a pipeline burst or overwatering landscapes. Loss of vegetation to fire or drought may cause an area to be more vulnerable to landslides. Vegetation

holds soil in place and without the root system of trees, bushes, and other plants, the land is more likely to slide away.107
One type of landslide that is different from debris flows or rock flows is deep-seated landslides.

Deep-seated landslides are not necessarily triggered by any single storm or earthquake. Rather, these types of landslides occur weeks to months after heavy rainfall ends, when water has had time to percolate deeper under the surface to saturate weak zones of rock. This creates a “landslide plane” under the saturated weight of the overlying rock and soil.108 The landslide plane may often be associated with earlier slides and can occur regardless of whether rain is occurring or not. As these landslides begin so deeply, they tend to carry more material and cover more territory than other types of slides. Deep-seated landslides generally occur on moderately steep slopes, travel much slower than mudflows or debris flows, and can continue for several days.

Regardless of the cause or specific form, a landslide can damage or destroy structures or roadways in its path. Underground infrastructure, such as pipelines or telecommunication lines, may be severed during a landslide. This could lead to infrastructure induced flooding if water pipes or sewage lines burst. In addition to property damage, landslides can crush or bury people, creating a risk of serious injury or death.

Landslide potential zones are mapped throughout the City of Grand Terrace; refer to Figure 4-11, Deep-Seated Landslide Hazard Zone. Landslide susceptibility classes combine rock strength and slope steepness to indicate relative hazard. Lower classes represent gentle slopes or stronger rock with low susceptibility, while higher classes (VIII–X) denote steep slopes or weaker rock where landslide potential is greatest, with active landslides assigned to Class X. Mapped landslide risk areas primarily include steep slopes located on the eastern side of the City near the foot of Blue Mountain. These areas have also historically suffered from severe erosion. Landslide susceptibility areas are primarily concentrated along the eastern and northeastern borders of the City, where the land is steep and unstable.

The extent of a landslide incident is largely dependent on the quantity of slope failure, measured in cubic meters or yards. Greater landslide extents will be associated with larger quantities of slope failure.

As identified in the previous LHMP, the following areas continue to be primary locations of concern for the landslide hazard within the City of Grand Terrace:
• East Canal Street: Undermining is occurring on the west side, causing erosion.

Maintenance of the shoulder bed needs improvement.
• Mount Vernon Avenue: Sloughing occurs on both sides just north of East Canal Street.

The western cut slope is unstable and frequently causes landslides. The area to the west is the City of Colton, while the east side is shared by the City of Grand Terrace and the City of Colton.
107 National Geographic Society, Landslide, https://education.nationalgeographic.org/resource/landslide/, updated 2024, accessed June 28, 2024.
108 California Department of Conservation, 2023 California Landslide Response, https://www.conservation.ca.gov/cgs/landslides/2023, accessed August 14, 2024.

• Vista Grande Way: Severe undermining and erosion occur near Grand View Baptist Church. Runoff from the church property undermines the road and sends debris into the church parking lot. The shoulder width varies from 25-30 feet to 2.5 feet. Some houses along Vista Grande have experienced erosion.
• Barton Road at Colton Border: Mudslides on Barton Rd. at the Colton border interfere with emergency transportation. Landslides and mudslides from both sides have blocked Barton Ave., making it impassable.
• Vivienda and Burns Avenue: Slope stability issues are present at Vivienda Ave. and Burns Ave. Runoff from the freeway affects slope stability. This area has flooded in the past, making the road impassable.

Figure 4-11
Deep-Seated Landslide Hazard Zones

While landslide events do not affect Grand Terrace as commonly as other hazard events, the following occurrences below details landslide, mudslide, rockslide, and washout events that have impacted the City in recent history:

In April 2020, San Bernardino County experienced heavy storm conditions, including the City of Grand Terrace. The Riverside metropolitan area near the City of Grand Terrace received 1.5 inches of rainfall whereas the City of San Bernardino received 1.92 inches of rainfall.109 Landslides and mudslides were reported as a result of this storm event.

In February 2024, the City of Grand Terrace as a part of a County wide effort braced for heavy rain and storm conditions in early February 2024. Fire Station 23 offered free sandbags to residents, and landslides and mudslides were reported as a result of this storm event.110 Two state declared disasters related to landslides have impacted the planning area within the last five years:
• State of Emergency: Severe Winter Storms – January 10, 2023 • State of Emergency: Severe Winter Storms – March 1, 2023 Several federally declared disasters related to landslides have impacted the planning area within the last five years. A list of federally declared disasters related to landslides is included below; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area for further details regarding specific impacts (if any) to the City of Grand Terrace.111 • EM 3591-CA: California Severe Winter Storms, Flooding, and Mudslides – January 9, 2023
• EM 3592-CA: California Severe Winter Storms, Flooding, and Mudslides – March 10, 2023 • DR-4699-CA: California Severe Winter Storms, Straight-line Winds, Flooding, Landslides, and Mudslides – April 3, 2023
• DR-4769-CA: Severe Winter Storms, Tornadoes, Flooding, Landslides, and Mudslides – April 13, 2024
As future development occurs near steep slopes, the probability of washouts, sloughing, erosion, rockslides, and landslide events occurring in the City is expected to increase. Mismanaged intense residential and recreational development in sloped areas such as Blue Mountain could increase the frequency of damaging landslides occurring in the City. Developing land outside of the medium to high landslide susceptibility areas will be critical to reducing the frequency and probability of future landslide events.
109 Daily Bulletin, Inland Empire weather forecast: rain, snow, thunderstorms, https://www.dailybulletin.com/2020/04/08/inlandempire-weather-rain-snow-thunderstorms/, updated April 8, 2020, accessed September 26, 2024. 110 NBC Los Angeles, Preparing for SoCal storms? Here is a list of fire stations offering free sandbags, https://www.nbclosangeles.com/weather-news/preparing-for-socal-storms-here-is-a-list-of-fire-stations-offering-freesandbags/3328314/, updated February 2, 2024, accessed September 20, 2024. 111 FEMA, Disaster Declarations for States and Counties, https://www.fema.gov/data-visualization/disaster-declarations-states-andcounties, accessed August 9, 2024.

Given the location of the planning area and based on previous landslide events, there is a likely probability of a landslide event significantly affecting the City of Grand Terrace. A likely probability means there is between 10 and 100 percent probability in next year or has a recurrence interval of 10 years or less. The LHMP planning team assigned a medium hazard planning consideration to the hazards and impacts associated with landslide events based upon a likely probability and expected impacts of future events.

Landslides are generally caused by one of two factors: seismic activity and soil saturation.

Earthquakes and ground shaking are not linked to climate change, however, heavy rains are affected by climate change and understood to contribute to saturated soils and landslides. Climate change is linked to increased precipitation and more frequent and/or severe storms. California is already experiencing climate changing impacts with increasing variable precipitations and becoming the highest variability of year-to-year precipitation in the contiguous United States.112 Increased rainfall due to climate change will lead to saturated slopes, erosion, and likely will exacerbate the effects of landslide and rockfall within the planning area.

As mudslides are affected by rain and wildfire, climate change can indirectly increase the risk of mudslides.113 As climate change affects the severity and intensity of wildfires, more vegetation is burned reducing soil stability. This allows for more debris to slide down during a mudslide. Overall, changing weather patterns and other related impacts of climate change may exasperate the impacts of the landslide hazard on populations and assets within the planning area in the future.

Critical facilities located within the landslide hazard zone primarily include those that serve as safety and security, food, hydration, shelter, and health and medical community lifelines. In total, there are 23 vulnerable critical facilities located within the City’s landslide hazard zone.

Government service and parks and recreation are the primary asset types within the landslide hazard zone, however other types of critical facilities have also been identified as vulnerable.

Critical facilities located within the City’s identified landslide hazard zone have been listed in Table 4-15, Landslide Vulnerability Summary.

Approximately 1,877 residential units are located within the landslide hazard zone. The number of vulnerable residential units multiplied by the average of 2.77 persons per household for Grand Terrace indicates that approximately 5,198 people reside in the landslide hazard zone.

Additionally, approximately 201,234 square feet of non-residential structures are located within the landslide hazard area. Refer to Table 4-15, Landslide Vulnerability Summary for a summary of vulnerable residents, residential units, and non-residential buildings. 112 California Climate Adaptation Strategy, Summary of Projected Climate Change Impacts on California, https://climateresilience.ca.gov/overview/impacts.html#:~:text=California%20is%20already%20experiencing%20the,have%20increa sed%20as%20temperatures%20warm, accessed June 28, 2024. 113 The Atlantic, A Recipe for Climate Disaster, https://www.theatlantic.com/science/archive/2022/03/climate-change-heavy-rainlandslides-flood/629404/, published March 29, 2022, accessed August 14, 2024.

Table 4-15
Landslide Vulnerability Summary
Critical Facilities at Risk
Map ID Name Asset Type Community
Lifeline Replacement Value
1 Grand Terrace City
Hall
Government
Service Safety and Security $7,276,800
2 San Bernardino
County Library Grand
Terrace Branch
Government
Service Safety and Security $1,917,850
4 San Bernardino
Sherriff Dept
Substation
Government
Service Safety and Security $8,534,160
5 Richard Rollins Park Parks and
Recreation Safety and Security Not Available
8 Griffin Park Parks and
Recreation Safety and Security Not Available
9 Susan Petta Park Parks and
Recreation Safety and Security Not Available
11 Grand Terrace Dog
Park
Parks and
Recreation Safety and Security Not Available
12 TJ Austin Park Parks and
Recreation Safety and Security Not Available
13 Grand Terrace
Elementary School Public School Safety and Security $14,984,328.42 14 Terrace View
Elementary School Public School Safety and Security $10,059,912.45 17 Grand Terrace Health
Care Center
Health Care
Center Health and Medical $3,000,695
19 Blue Mountain Senior
Villas
Senior Living
Facility
Food, Hydration,
Shelter $3,000,695
20 San Manuel Indian
Health Clinic
Health Care
Center Health and Medical $3,000,695
21 JC Wallace House Senior Living
Facility
Food, Hydration,
Shelter $3,000,695
22 SCE Vista Substation Electric
Substation Energy $3,000,695
24 RHW Water Tank Potable Water Water Systems $1,500,000 25 RHW Water Tank Potable Water Water Systems $1,500,000 26 RHW Water Tank Potable Water Water Systems $1,500,000 29 Azure Hills SeventhDay Adventist Church Church Food, Hydration, Shelter $3,775,700
30 Grand View Baptist
Church Church Food, Hydration, Shelter $3,775,700
32 Christ the Redeemer
Catholic Church Church Food, Hydration, Shelter $3,775,700 33 St. Junipero Serra
House of Formation Seminary Food, Hydration, Shelter $3,775,700 37 Railroads Railway Transportation Not Available
Populations at Risk
Residents at Risk Residential Units at Risk Non-Residential Area at Risk (Sq.

Ft.)
5,198 1,877 201,234

Potential impacts of a landslide in the City would include significant damage to buildings and infrastructure, including critical facilities that provide water, safety and security, transportation, food, hydration, and shelter. Specific critical facilities located within the landslide hazard zone include parks, churches, schools, senior living facilities, health care centers, potable water assets, and an electric substation. Damages to these types of buildings would hinder City operations, emergency response, water services, and compromise the care of elderly and disabled residents within the City. A landslide event would also potentially result in damaged homes and businesses.

Potential impacts would include the displacement of a significant number of people, disruption of power, water, and emergency services, economic losses, ground destabilization, and increased insurance premiums. Major transportation routes, including Interstate 215 and railroads, could become severely congested, temporarily blocked, or inaccessible, complicating evacuation efforts, especially for socially vulnerable populations. Landslide debris could cause medical emergencies by throwing dust and debris into the air and potentially affecting the health of nearby populations. Shelters designated for emergencies may be damaged or destroyed by landslides, increasing the risk of secondary hazards like dust inhalation for the local population.

Changes in Vulnerability
Changes in land use, development and population since the previous LHMP indicate past changes in hazard vulnerability within the planning area. Refer to Section 3.5, Development Trends and Future Development for a description of past and future growth within Grand Terrace.

To summarize changes in development and population in the last five years, the City population has increased by 8.84 percent. The City has also experienced development and housing growth and has initiated various capital improvement projects. Changes in land use and capital improvement projects have enabled development and population growth within the planning area, particularly between Van Buren and De Berry Street, which contain areas that intersect with the landslide hazard area. Land uses intersecting with the hazard zone include residential, commercial, and public facilities. Based on population changes and development trends, it is reasonable to assume that vulnerability to landslide and rockfall has increased due to population and density increases since the 2017 LHMP.

Anticipated development and capital improvements in the next five years will enable more population growth and increased density within Grand Terrace into the future. Population and residential development are anticipated to increase in accordance with the California Department of Housing and Community Development (HCD) Regional Housing Need Allocation (RHNA). The RHNA anticipates an additional 630 housing units in the City of Grand Terrace between 2021 and 2029.

Mapped landslide hazard zones primarily include residential areas and open space followed by industrial areas. Population and density within the mapped landslide hazard zone between Van Buren and De Berry Street is expected to experience growth and continued development over the 5-year planning horizon of this LHMP. Considering the potential for population growth, additional development, increased density, and anticipated capital improvement projects throughout the City and particularly within areas intersecting with the landslide hazard area, it is reasonable to assume that vulnerability to landslide and rockfall will increase over the planning horizon of this LHMP.

Section 3.6, Socially Vulnerable Populations and Determination, includes a detailed determination of socially vulnerable populations (SVP) within the planning area and the characteristics that make those populations more vulnerable to hazards. Mapped landslide hazard zones primarily impact the eastern portions of the City which primarily consists of Census Tract 71.04 a “Low-Medium” by the CDC Social Vulnerability Index (SVI). Additionally, landslide hazard zones are also located within Census Tracts 71.11, 71.07 and 40.04, which are ranked as “Medium-High” (71.11) and “High” (71.07 and 40.04) by the CDC SVI. However, emergency response operations during a major landslide event may impact the entirely of the City. SVPs including persons below 150 percent poverty level, unemployed civilians, housing cost-burdened individuals, populations with limited English, persons aged 65 and older, persons aged 17 and younger, persons with no high school diploma, single-parent households with children under 18, minority population, and in overcrowded housing exist throughout the City and may be particularly vulnerable to landslide.

The primary concern for SVPs and other high-risk individuals in the City would be evacuations, structure stabilization, and access to resources during a major landslide event.

Socially vulnerable populations face unique challenges during landslide events. Unemployed individuals and those below the poverty level often lack resources for adequate preparation and evacuation. Elderly persons may have mobility issues and chronic health conditions that complicate evacuation efforts. Individuals with housing in structure with 10 or more units or in overcrowded housing may have limited evacuation routes and may face risk of trampling during evacuations. Populations with limited English proficiency may face challenges with emergency warnings and evacuation instructions. Single-parent households with children under 18 may have limited resources for emergency supplies and evacuation. Unhoused populations are particularly vulnerable due to their lack of shelter and access to emergency services. These factors necessitate targeted support and accessible communication to ensure the safety and well-being of these groups during landslide events.

The US Geological Survey (USGS) defines an earthquake as a sudden slip on a fault and the resulting ground shaking and radiated seismic energy caused by the slip (or any other sudden stress changes in the earth).114 Faults are fractures along the earth’s crust between two blocks of earth and can be defined as a strike slip, normal, or thrust faults. Earthquakes occur without warning, and result in effects such as fault rupture, ground motion, liquefaction, and landslides.

Fault Rupture
Fault rupture or surface faulting is the differential movement of two sides of a fracture, where the ground breaks apart. The length, width, and displacement of the ground characterize surface faults, which occur based on the type of underlying fault. Faults occur at boundaries between large sections of the earth’s surface, called tectonic plates. Most of California underlies the North 114 USGS, The Science of Earthquakes, https://www.usgs.gov/programs/earthquake-hazards/scienceearthquakes#:~:text=The%20surface%20where%20they%20slip,Sometimes%20an%20earthquake%20has%20foreshocks., accessed September 19, 2024.

American plate, however, the City of Grand Terrace is located on the Pacific plate. The San Andreas Fault is the main boundary between North American and Pacific plates, but other fault lines can be found up to 200 miles away. The presence of the San Andreas Fault and other regional faults is the reason for frequent seismic activity in California.

Where surface traces of active faults are found in California, an Alquist-Priolo fault zone is mapped. A regulatory zone, which is a 500-foot buffer, is then created around the mapped AlquistPriolo fault zone.115 If an active fault has a potential for surface rupture, a structure for human occupancy cannot be placed over the fault and must be a minimum distance from the fault (generally fifty feet). The intent of the Alquist-Priolo Act is to reduce losses from surface fault rupture, and to prevent the construction of buildings used for human occupancy on the surface trace of active faults. Before a new development is permitted, cities and counties require a geologic investigation to demonstrate that proposed buildings will not be constructed on active faults. 116
Ground Shaking
Ground motion is the movement of the earth's surface from earthquakes. Ground motion is produced by seismic waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth and along its surface.117 Seismic waves produce ground vibrations above the surface. The severity of the vibration increases with the amount of energy released and decreases with distance from the causative fault or epicenter. Soft soils can further amplify ground motion.118
Seismic shaking can be strong enough to result in widespread devastation or be virtually undetectable by the average person. The intensity of seismic shaking is a result of the release by the fault rupture (how much of the accumulated stress was released), the length of the rupture (the longer the slip along the fault line, the greater the shaking), and the depth at which the rupture occurs (ruptures that occur closer to the surface often cause stronger shaking). Usually, areas closest to the site of the rupture experience the greatest shaking, although differences in geology and soil can also have an impact. Seismic shaking can damage or destroy buildings and structures and may cause partial or total collapse. Ground movement can damage or destroy infrastructure on or beneath the surface, such as roads, rail lines, and utility lines and pipes. This in turn, can cause hazardous materials releases, water main breaks, and other dangerous situations resulting from infrastructure failure. Falling debris and structures also create a risk of injury or death.

Liquefaction
Liquefaction occurs when ground shaking causes saturated soils, primarily clay-free deposits such as sand or silt, to lose strength and act like a viscous fluid. Certain soils are more susceptible 115 California Department of Conservation, Alquist-Priolo Earthquake Fault Zones, https://www.conservation.ca.gov/cgs/alquistpriolo, accessed September 19, 2024. 116 USGS, Alquist-Priolo Faults, https://earthquake.usgs.gov/education/geologicmaps/apfaults.php, accessed September 19, 2024. 117 USGS, Earthquake Glossary – Ground Motion, https://www.usgs.gov/glossary/earthquake-hazardsprogram#:~:text=of%20the%20ground.-,Ground%20motion,earth%20and%20along%20its%20surface., accessed September 19, 2024.
118 FEMA, Multi-Hazard Identification and Risk Assessment - Subpart D: Seismic Hazards, file:///C:/Users/Audrey.tamayo/Downloads/481396.pdf, January 1, 1997.

to liquefaction, particularly younger and looser sediment closer to the water table. According to FEMA, liquefaction causes three types of ground failure, as described below:
• Lateral spreads involve the lateral movement of large blocks of soil as a result of liquefaction of an underlying layer. They generally develop on gentle slopes, most commonly between 0.3 and 3 degrees. Horizontal movements commonly are as much as 10 to 15 feet. However, where slopes are particularly favorable, and the duration of ground shaking is long, lateral movement may be as much as 100 to 150 feet. Lateral spread usually breaks up internally, forming numerous fissures and scarps. • Flow failures consist of liquefied soil or blocks of intact material riding on a layer of liquefied soil and are the most catastrophic type of ground failure caused by liquefaction. They commonly move several feet and up to dozens of miles under certain conditions. Flow failures usually form in loose saturated sands or silts on slopes greater than three degrees. • Loss of bearing strength occurs when the soil supporting buildings or other structures liquefies. When large deformations occur, structures settle and tip. The general subsurface geometry required for liquefaction-caused bearing failures is a layer of saturated, cohesionless soil that extends from near the ground surface to a depth equal to about the width of the building.

Fault Rupture/Ground Motion
Ground motion would be particularly damaging to residential buildings constructed of wood or reinforced masonry construction, and to mobile homes. Other buildings that do not typically perform well in earthquakes are soft-story buildings. These types of buildings have a story (typically the first floor) that lacks adequate strength or toughness due to too few shear walls.

The most common measures of ground shaking during an earthquake event, the Richter Magnitude and Modified Mercalli Intensity scales, are described below. In addition, mapped areas most at risk for fault rupture and ground shaking are discussed below.

The City is located within the Southern California region, known to be seismically active. There are no faults that traverse the City however, the City is near many active faults such as the San Jacinto fault zone, Crafton Hills fault zone, and the San Andreas fault zone. Table 4-16, Local Earthquake Faults Within 25 Miles of Grand Terrace, lists each active and potentially active fault near the City of Grand Terrace, distance to the City, type of faulting, last major rupture, slip rate, interval between major ruptures, and estimated magnitude.

Table 4-16
Local Earthquake Faults Within 25 Miles of Grand Terrace Fault
Name
Distance1
(miles)
Type of
Faulting
Last Major
Rupture
Slip
Rate
(mm/yr)
Interval
Between Major
Ruptures
Estimated
Magnitude2
(Mw)
San
Jacinto
Fault

0.2 Right-lateral
strike-slip
April 9, 1969,

6.5 Mw on
Coyote Creek
segment
7 – 17 100 – 300 years,
per segment 6.5 – 7.5

Fault
Name
Distance1
(miles)
Type of
Faulting
Last Major
Rupture
Slip
Rate
(mm/yr)
Interval
Between Major
Ruptures
Estimated
Magnitude2
(Mw)
San
Andreas
Fault
Zone

9.5 Right-lateral
strike slip
January 9,
1857 (Mojave
segment);
April 18, 1906
(Northern
segment)
About 20
-35
Average of
about 140 years
on the Mojave
segment;
recurrence
interval varies
greatly -- < 20
yrs (at Parkfield
only) – 300+ yrs

6.8 - 8.0
Sierra
Madre
Zone

11.7 Reverse Holocene 0.36 –

4.0 Estimated
several
thousand years

6.0 – 7.0
Red-Hill
Etiwanda
Avenue
Fault

13.1 Thrust Late
Quaternary Unknown Unknown 6.0 – 7.0
Elsinore
Fault
Zone

18.5 Right-lateral
strike-slip
May 15, 1960,

6.0 Mw
Roughly

4.0 Roughly 250
years

6.5 – 7.5
San Jose
Fault 22.75
Left-lateral
strike-slip;
minor
reverse
component
possible
February 28,
1990, 5.4 ML

0.2 – 2.0 Unknown 6.0 – 6.5 ML
Banning
Fault 23 Right-lateral strike-slip Holocene Unknown Unknown 6.0 – 7.2 Notes:

1. Estimated Distance

2. In Mw (Moment Magnitude)
Source: Southern California Earthquake Data Center, Earthquake Information, https://scedc.caltech.edu/earthquake/faults.html, accessed September 23, 2025.

The list below shows more information on more researched faults, however, unknown fault lines included in the list may pose a grave threat to the planning area as well. • The San Jacinto Fault Zone runs from San Bernardino to the Superstition Mountains south of the Salton Sea and is approximately 0.2 miles from the City at its closest point. The last major event along this fault was the Borrego Mountain earthquake in 1968, which measured 6.5 on the moment magnitude scale. The Southern California Earthquake Data Center estimates that major events along this fault could measure 6.5 to 7.5 on the moment magnitude scale.
• The Crafton Hills Fault Zone is about 20 km, consisting of at least 10 faults. This fault is caught between a wedge between the San Andreas fault and the San Jacinto fault zone which both have a right-lateral slip. Thus, the area between the two, near the intersection, is being pulled apart.119
119 Southern California Earthquake Data Center, Crafton Hills Fault Zone, https://scedc.caltech.edu/earthquake/craftonhills.html, accessed September 30, 2024.

• The San Andreas Fault, the largest and most well-known of California’s faults, runs from Cape Mendocino to the Salton Sea. It is approximately 9.5 miles from the City at its closest point. It has caused numerous major earthquakes throughout California’s history, including the 1906 San Francisco earthquake that destroyed much of that city and the 1989 Loma Prieta earthquake that caused widespread damage in the San Francisco Bay Area. The central portion of the San Andreas Fault was responsible for an earthquake measuring an estimated 7.9 on the moment magnitude scale, the strongest in California’s recorded history in 1857 near the town of Parkfield (approximately 170 miles from the City). The Southern California Earthquake Data Center estimates that a future major event along the southern part of the San Andreas Fault could measure 6.8 to 8.0 on the moment magnitude scale. The recurrence interval along the fault varies greatly, from less than 20 years to more than 300 years between events.120
• The Whittier-Elsinore Fault Zone runs from the Chino Hills region to the California-Mexico border and is approximately miles from the City at its closest point. Near Chino Hills it splits into two separate segments, the Chino Fault and the Whittier Fault. This fault is believed to cause a major event approximately every 250 years with a probable magnitude of 6.5 to 7.5.121 The last major event along this fault was a 1910 earthquake measuring an estimated 6.0 on the moment magnitude scale.
• The Sierra Madre Fault Zone runs along the southern edge of the San Gabriel Mountains from La Cañada-Flintridge to Claremont, approximately 16 miles from the City at its closest point. It is made up of five segments; scientists are unclear if any event along this fault could be limited to one segment or if events along multiple segments are possible. The last major event along the Sierra Madre Fault Zone is believed to have happened within the past 10,000 years, although no specific event is known. The Southern California Earthquake Data Center estimates that it is capable of producing an event measuring 6.0 to 7.0 on the moment magnitude scale.122
• Red Hill Fault also known as the Etiwanda Avenue Fault is a 25 km long fault that is often considered to be a part of the Cucamonga fault zone.123 Alquist-Priolo Fault Zones
Alquist-Priolo earthquake fault zones are regulatory zones surrounding the surface traces of active faults in California as mapped and defined by the California Department of Conservation.

The City of Grand Terrace is not located within an Alquist Priolo Fault Zone; however, the City’s northern and eastern boundary is near the Alquist Priolo Fault Zone due to the presence of the San Jacinto Fault; refer to Figure 4-12, Earthquake Epicenters.

There are two scales commonly used by scientists to measure earthquakes: the Moment Magnitude Scale and the Modified Mercalli Intensity Scale. The moment magnitude scale is based on the now largely unused Richter scale and measures the amount of energy released by the earthquake. The Modified Mercalli Intensity Scale (MMI Scale) measures the effects of the earthquake and is based on qualitative observations rather than a mathematical basis. The 120 Southern California Earthquake Data Center, San Andreas Fault Zone, https://scedc.caltech.edu/earthquake/sanandreas.html, accessed July 23, 2024.
121 Southern California Earthquake Data Center, Elsinore Fault Zone, https://scedc.caltech.edu/earthquake/elsinore.html, accessed July 23, 2024.
122 Southern California Earthquake Data Center, Sierra Madre Fault Zone, https://scedc.caltech.edu/earthquake/sierramadre.html, accessed July 23, 2024.
123 Southern California Earthquake Data Center, Red Hill Fault, https://scedc.caltech.edu/earthquake/redhill.html

intensity scale consists of a series of certain key responses such as people awakening from sleep, movement of furniture, damage to chimneys, and destruction. Although numerous scales have been developed to evaluate earthquake effects, the scale currently used in the United States is the Modified Mercalli Intensity Scale. This scale, composed of twelve increasing levels of intensity ranging from imperceptible shaking to catastrophic destruction, is designated by Roman numerals I through XII. Table 4-17, Modified Mercalli Intensity Scale, shows the different categories of the Mercalli intensity scale.

Table 4-17
Modified Mercalli Intensity Scale
Intensity Shaking Description/Damage
I Non felt Not felt except by a very few under especially favorable conditions.

II Weak Felt only by few persons at rest, especially on upper floors of buildings.

III Weak Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.

IV Light Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound.

Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V Moderate Felt by nearly everyone; many awakened. Some dishes, windows broken.

Unstable objects overturned. Pendulum clocks may stop.

VI Strong Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

VII Very
Strong
Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII Severe Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls.

Heavy furniture overturned.

IX Violent Damage considerable in specifically designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.

X Extreme Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.

Source: USGS, The Modified Mercalli Intensity Scale, https://www.usgs.gov/natural-hazards/earthquakehazards/science/modified-mercalli-intensity-scale?qt-science_center_objects=0#qt-science_center_objects, accessed December 18, 2024.

Magnitude and intensity measure different characteristics of earthquakes but often correlate.

Magnitude measures the energy released at the source of the earthquake, determined by measurements on seismographs. Intensity measures the strength of shaking produced by an earthquake at a certain location and is determined by effects on people, structures, and the natural environment. Refer to Table 4-18, Moment Magnitude and Modified Mercalli Intensity Scale Comparison, which lists the intensities that are typically observed at locations near the epicenter of earthquakes of different magnitudes.

Table 4-18
Moment Magnitude and Modified Mercalli Intensity Scale Comparison Moment Magnitude Typical Maximum Modified Mercalli Intensity

1.0 – 3.0 I

3.0 – 3.9 II – III

4.0 – 4.9 IV – V

5.0 – 5.9 VI – VII

6.0 – 6.9 VIII – IX

7.0 or higher X or higher
Source: USGS, Earthquake Magnitude, Energy Release, and Shaking Intensity, https://www.usgs.gov/naturalhazards/earthquake-hazards/science/earthquake-magnitude-energy-release-and-shaking-intensity?qtscience_center_objects=0#qt-science_center_objects, accessed December 18, 2024.

Figure 4-12
Earthquake Epicenters

Figure 4-13
Seismic Fault Zones Near Grand Terrace

Liquefaction
The potential for liquefaction exists in areas susceptible to ground shaking with loose soils and/or shallow groundwater. Given the active faults in the region, and the presence of geologically young, unconsolidated sediments, liquefaction is possible throughout the City. The San Bernardino County Land Use Plan identified the City of Grand Terrace as a part of the generalized liquefaction susceptibility zone in 2009. Figure 4-14 shows the Blue Mountain and northern half of the City to have low liquefaction susceptibility while the northwestern portion of the City has medium generalized liquefaction susceptibility. The liquefaction hazard does not have a specifically identified hazard zone and could therefore potentially impact the entire planning area.

Figure 4-14
San Bernardino County Geological Hazard Overlays Liquefaction including the City of Grand Terrace
Source: Geological Hazard Overlays, San Bernardino County Land Use Plan, General Plan, https://www.sbcounty.gov/Uploads/lus/GeoHazMaps/EHFHC_20100309new.pdf, published 2009, accessed December 18, 2024
Fault Rupture & Ground Shaking
Table 4-16, Significant Historical Earthquakes in Southern California, identifies the major earthquakes that have occurred in southern California. As shown in Table 4-X, multiple regional

major earthquakes over the past two decades have resulted in seismic ground shaking in the City of Grand Terrace.

Table 4-19
Significant Historical Earthquakes in Southern California Earthquake Name Year Estimated Magnitude
Elsinore 1910 6.0
San Jacinto 1918 6.8
North San Jacinto 1923 6.3
Long Beach 1933 6.4
San Fernando 1971 6.5
Whittier Narrows 1987 5.8
Newport Beach 1989 4.7
Landers Earthquake 1992 7.3
Big Bear Earthquake 1992 6.3
Northridge 1994 6.7
Hector Mine Earthquake 1999 7.1
Yorba Linda 2002 4.6
Chino Hills 2008 5.4
Ridgecrest Sequence 2019 7.1
San Jacinto Fault Zone
Earthquake
2020 4.9
Source: Southern California Earthquake Data Center, Significant Earthquakes and Faults, http://scedc.caltech.edu/significant/index.html, accessed September 30, 2024.

Two recent earthquakes occurred near the City of Grand Terrace that were both under 5 Mw. In March 2022, a 3.4 Mw earthquake occurred in the City of Rancho Cucamonga approximately 25 miles from the City of Grand Terrace.124 A 2.9 aftershock followed this earthquake. The depth of the quake was 4.3 miles. Light shaking was felt as far west as the City of South Gate, as far south as Laguna Beach and east in Redlands. Additionally, in July 2022, a 3.3 Mw earthquake occurred in the Inland Empire. A 2.9 aftershock was reported an hour later.125 Liquefaction
Comprehensive, historic accounts of damage within the City of Grand Terrace from liquefaction are not readily available. San Bernardino County has had instances of liquefaction but not near the City of Grand Terrace. The County also depicts low generalized liquefaction susceptibility in the City, with medium susceptibility along the Interstate 215 in the western portion of the City.126 No federally declared or state declared disasters related to liquefaction have occurred including the City of Grand Terrace within the last five years; refer to Table 4-24, Summary of Federally Declared Disasters Affecting the Planning Area.
124 KTLA 5, 3.4 magnitude earthquake shakes up Inland Empire, https://ktla.com/news/local-news/3-4-magnitude-earthquakeshakes-up-inland-empire/, published March 22, 2022 accessed September 30, 2024. 125 NBC Los Angeles, Rancho Cucamonga Earthquake Rattles Inland Empire Today, https://www.nbclosangeles.com/news/local/rancho-cucamonga-earthquake-today-inland-empire/2938504/, published July 14, 2022, accessed July 14, 2022.
126 San Bernardino County Land Use Plan, General Plan Geological Hazards Overlays, https://www.sbcounty.gov/Uploads/lus/GeoHazMaps/EHFHC_20100309new.pdf, published 2010, accessed October 2, 2024.