The California Communities Extreme Heat Scoring System (CalHeatScore) is a new public health tool to help protect people from extreme heat. CalHeatScore provides the public with information to help plan and prepare for extreme heat events, including information about life-saving resources to help protect at-risk populations. CalHeatScore uses historical climate, forecasted weather, and health data to score heat events based on their intensity and potential impact on health. CalHeatScore creates an easy-to-understand scale of 0 to 4 for all ZIP codes in California, every day, to communicate heat risks. CalHeatScore also connects people to locally relevant resources, such as cool centers, so that they can be prepared when dangerous heat occurs.

CalHeatScore is being developed to reduce heat-related illness and save lives by translating meteorological, weather and health data into easy-to-understand heat risk alerts. This tool raises awareness of extreme heat events and empowers parents, seniors, caregivers, and communities to plan for, mitigate, and survive extreme heat events. CalHeatScore is committed to prioritizing the most vulnerable populations and ensuring that everyone has the information they need to stay safe during extreme heat. The CalHeatScore mapping tool prototype was released on December 31, 2024.

CalHeatScore is a public health tool that translates local weather and health data into information that the public can use. Here’s how it works:

• Localized Heat-Health Thresholds: Provides temperature thresholds that indicate the health risks of heat that are specific to California communities at the ZIP code level.
• Daily Updates: Delivers updated daily forecasts of heat risk related to localized increases in expected heat-related illnesses.
• Local Population Profiles: Provides local sociodemographic profiles on some of those most impacted by heat, including children, older adults, outdoor workers, linguistically isolated, and those without health insurance.
• Resource Connections: Points users to locally relevant resources, such as the locations of cool centers.

CalHeatScore is designed specifically for California’s unique needs:

• Locally Relevant Data: Provides ZIP code-level rankings of the severity of heat events that are tailored to California’s diverse microclimates and populations. Also includes supplemental data which identifies proportions of different populations more sensitive to extreme heat.
• Resource Integration: Connects users to locally relevant resources, such as cool centers. Centralizes access to heat-related resources across multiple government departments.

The Office of Environmental Health Hazard Assessment leads the effort to develop CalHeatScore with support from:

• Office of Land Use and Climate Innovation: Consults on communication strategies and partnerships.
• Department of Insurance: Provides data and insights from a 2024 report on insurance gaps relating to heat.
• Department of Public Health (CDPH): Offers recommendations on local applications of the tool.
• Office of Emergency Services (CalOES): Assists in communications and dissemination plans.
• In addition to these specific roles, all state agencies listed provide input on improvements to CalHeatScore.
• Additional collaborators contributing to the development of the CalHeatScore system include the UCLA Center for Health Climate Solutions and researchers at Oregon State University and Applied Climatologists, Inc.

A public engagement process to further refine the tool based on stakeholder input will begin in early 2025.

While still a prototype, CalHeatScore can already be used to stay safe during extreme heat. Users are encouraged to:

• Access daily updates and heat rankings.
• Use the tool to find local resources like cool centers.
• Provide feedback to help improve future versions.

Users can share their experiences and suggestions to help improve CalHeatScore. Opportunities to provide feedback will be available on the CalHeatScore website and at community outreach events.