The California Heat Assessment Tool

California’s climate is warming and residents increasingly endure extreme heat events that adversely impact public health. This exacerbates existing risks and will bring new challenges for different regions in the state, threatening the efficacy of traditional intervention strategies. Current thresholds for heat alerts are based on temperatures that exceed historical statistical thresholds, rather than temperatures that cause public health impacts. These ‘health-neutral’ thresholds may underestimate the health risks for the most sensitive populations. The California Heat Assessment Tool (CHAT) is based on new research that establishes local, health-based thresholds for extreme heat that help public officials, health professionals and residents understand what changing conditions mean for them. CHAT is part of California’s Fourth Climate Change Assessment, a state-mandated research program to assess climate change impacts in California, and was developed by Four Twenty Seven, Argos Analytics, the Public Health Institute and Habitat 7 with technical support from the California Department of Public Health.

Explore CHAT at  This online tool advances the understanding of what types of heat waves pose public health risks and examines how the frequency and severity of local heat waves are expected to change over time due to climate change.

Read a brief report that shares key findings from the research and summarizes the data analysis visualized in the tool.

Access the technical report detailing technical methodology and view other projects funding by the California Fourth Climate Change Assessment.

Access the users needs assessment for a detailed explanation of the literature review and interview process that defines the data gap the research team addressed.

Download the full press release.