Governor Newsom expands access to life-saving CalHeatScore, a cutting-edge tool to keep Californians safe during extreme heat

What you need to know: During National Heat Safety Week and in advance of the Memorial Day holiday, California is taking action. Extreme heat is the leading cause of weather-related deaths in the nation, claiming more lives annually than any other climate threat, including fires and floods. CalHeatScore's new API feature puts live, ZIP-code level heat risk data directly into the hands of app developers, weather services, local governments, nonprofits, universities, and more to safeguard public health and keep our communities safe when temperatures rise.

SACRAMENTO - With summer around the corner and in the wake of a record-setting March 2026 heatwave, Governor Newsom today announced a new feature to integrate California Communities Extreme Heat Scoring System (CalHeatScore) data into a wide range of applications to help Californians stay safe during extreme heat.

CalHeatScore, released last year, is a cutting-edge tool to forecast and rank the risk hot weather poses to public health and connect Californians with available resources to stay safe during extreme heat events.

California is turning cutting-edge data and technology into real-world protection, giving people the power to see extreme heat coming and act early. As temperatures rise, this innovation helps safeguard lives, strengthen resilience, and ensure no one is left behind.

Governor Gavin Newsom

The new CalHeatScore application programming interface (API) gives app developers, weather services, local governments, nonprofits, universities, medical providers, emergency response entities, and data-driven reporters access to live data that can be integrated into a wide range of applications, such as community alerts, emergency response planning, and newscasts.

"With summer-like temperatures arriving in California in March, tools such as CalHeatScore and its API are more critical than ever," said OEHHA Director Kris Thayer. "Extreme heat is dangerous, and we are continually strengthening CalHeatScore to inform actions that protect residents from the impacts of extreme heat and build resilience in our most vulnerable communities."

CalHeatScore Forecast for Thursday, May 21

About CalHeatScore

In a hotter, drier world, connecting Californians with extreme weather information and resources has never been more important.

As part of a broader climate package in 2022, Governor Newsom signed Assembly Bill 2238 by Assemblymember Luz Rivas to codify the California Department of Insurance's Climate Insurance Workgroup recommendation by requiring the state to develop a statewide extreme heat ranking system.

In 2025, California became the first state in the nation - and one of the only jurisdictions in the world - to launch a heat-ranking system.

CalHeatScore, developed by the California Environmental Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA), brings together ZIP-code level data to provide locally tailored heat scores. It translates complex weather and health data into clear guidance and integrates other important data sets, like locations for the nearest cooling centers. CalHeatScore also provides local data on groups susceptible to extreme heat, such as older adults and children, to support community planning efforts and provides tips for staying safe, such as how to recognize signs of heat illness.

The API is part of continuous efforts to develop, improve and broaden options for using CalHeatScore and keep Californians informed about extreme heat in their communities.

Dangers of Extreme Heat

Extreme heat is the leading cause of weather-related deaths in the nation, claiming more lives annually than any other climate threat, including fires and floods. In 2024, California communities experienced the hottest summer on record in 130 years. According to a report from the Department of Insurance, from 2013 to 2022, seven extreme heat events resulted in nearly 460 deaths, over 5,000 hospitalizations and about 344 adverse birth outcomes.

State reports show a correlation between heat and a range of negative health effects including death, lower birth weight, and increased emergency room visits and hospitalizations for conditions ranging from heart conditions to poor mental health. Extreme heat also takes an economic toll on the state, with an estimated $7.7 billion of lost wages, agricultural disruptions, and power outages from 2013-2022.

State Response

With ongoing work on CalHeatScore, an update to California's Extreme Heat Action Plan moving forward, and a new round of the Extreme Heat and Community Resilience Program (EHCRP) from the Governor's Office of Land Use and Climate Innovation underway, among many other efforts, California continues to prioritize building resilience and climate action to protect communities.

In addition to CalHeatScore, you can learn more about actions you can take to protect yourself and others during extreme heat through Listos California and the California Department of Public Health.