Heat is the deadliest climate-driven hazard in California. To help Californians stay healthy when temperatures rise, the California Communities Extreme Heat Scoring System (CalHeatScore) will:

  • forecast coming heat waves
  • help people prepare and plan for extreme heat events
  • provide information about local resources

Help Improve CalHeatScore

On May 30, we will host the first in a series of opportunities for anyone interested to see how CalHeatScore will work. We invite community members, local and Tribal governments, researchers, nongovernmental organizations and others to share their ideas and feedback about CalHeatScore.

CalHeatScore Kick-Off Meeting

Thursday May 30, 2024
10 – 11:30 AM PDT

Participate in person: CalEPA Headquarters
Sierra Hearing Room
1001 I St, Sacramento, CA 95814

Participate online: Zoom Registration

Webcast (viewing only)

CalHeatScore Kick-off Presentation

Sign up to Receive Updates About CalHeatScore

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About CalHeatScore

Weather warning systems give people and communities time to plan ahead and can save lives.  CalHeatScore will increase awareness of local and regional extreme heat events by translating weather information into easy-to-understand health warnings. It will:

  1. Map heat risk across California communities with an interactive online interface.
  2. Update daily with temperature forecasts for early warning of heat waves.
  3. Set local health-protective thresholds of extreme heat by accounting for factors like:
    1. Regional and local climates.
    2. Duration of extreme heat, minimum nighttime temperatures, and seasonality.
    3. Where people most vulnerable to heat reside, such as children and elderly people or people with certain health conditions.
    4. Local health effects of heat, including heat-related illnesses.
  4. Connect people with locally relevant resources, such as nearby cooling centers and community pools.
  5. Use high-quality, publicly available data and be fully transparent, with all data, models, and methodology published online.

We are working with partners across state government to develop CalHeatScore. We will launch the initial prototype by January 1, 2025.

Other heat risk tools like the National Weather Service’s NWS HeatRisk will continue to be helpful to Californians, especially as we develop CalHeatScore. CalHeatScore will provide similar heat risk forecasts, while accounting for people's health challenges at a more local level and linking users to nearby resources. 

CalHeatScore will be a tool for individuals, communities, decision makers, policy makers and researchers, seeking up-to-date information about heat risks and tools to keep themselves and their communities safe.

About AB 2238

In 2021, the California Department of Insurance’s (CDI) Climate Insurance Workgroup recommended California build a system to rank heat waves to better communicate the deadly risks to Californians and help communities prepare, similar to how tropical storms and hurricanes are described by "category" level. 

Assembly Bill No. 2238 (L. Rivas, Chapter 264, Statutes of 2022) codified that recommendation by requiring CalEPA to develop an extreme heat ranking system and the Integrated Climate Adaptation and Resiliency Program (ICARP) to disseminate information to communities and local leaders. The CalHeatScore system is being developed in response to this mandate.

Thus, the bill requires CalHeatScore to be based on...

  1. available meteorological data on heat events, 
  2. data on the associated health impacts, 
  3. measures of extreme heat severity and its health impacts, 
  4. locally relevant information such as urban heat island effects; and
  5. public input. 

CalHeatScore is also required to include recommendations on thresholds or triggers for the implementation of policies that reduce health risks associated with extreme heat, recommendations for metrics to measure the short- and long-term impacts of extreme heat on human health and information from a CDI study (also required by AB 2238) into approaches that enable local governments to more fully insure local heat risks.

OEHHA on behalf of CalEPA is developing and maintaining CalHeatScore in consultation with ICARP, the California Department of Public Health (CDPH) and the Department of Insurance (CDI).

About Heat and Health

By mid-century, California's daily maximum average temperatures are expected to rise by 4.4ºF – 5.8ºF from their 1950 average. Heat waves that result in public health impacts are projected to last up to two weeks longer in the Central Valley and occur 4 to 10 times more often in the Northern Sierra region. In cities, heat waves are projected to cause 2-3 times more heat-related deaths.

Vulnerability to heat’s effects varies across regions, microclimates, and populations. Some areas are accustomed to hot temperatures while other areas that have been mild historically are experiencing warmer temperatures. For vulnerable populations, including elderly people, children, and those with certain health conditions, and for people with limited or no access to cooling or shade, extreme heat can be dangerous – even deadly.  For more information about the health effects of excessive heat, visit the Resources section.


OEHHA's mission is to protect and enhance the health of Californians and our state’s environment through scientific evaluations that inform, support and guide regulatory and other actions. We are creating CalHeatScore as part of California’s implementation of AB 2238.  For over a decade, we also have developed tools that synthesize environmental and socioeconomic data into statewide maps, such as CalEnviroScreen.  

We also have conducted studies into the health impacts of increased heat and tracked heat-related indicators of climate change. Our studies have shown associations between heat and a range of negative health affects including death, low birth weight, and increased emergency room visits and hospitalizations for conditions ranging from heart conditions to mental health. The studies also have helped identify populations that may be more vulnerable to heat-related deaths and illnesses, including older adults, pregnant people, infants and children, and people of color.

This research also has helped inform some of California’s other extreme heat efforts: Preparing California for Extreme Heat: Guidelines and Recommendations (2013)CalEPA Urban Heat Island Index Report (2015)CA Climate Adaptation Strategy , and the Extreme Heat Action Plan (2022)

Contact Us

Walker Wieland Portrait

Walker Wieland

Walker Wieland is the manager of the Extreme Heat Ranking System Development Section: CalHeatScore@oehha.ca.gov.

For media inquiries, please contact Amy Gilson: Amy.Gilson@oehha.ca.gov.