Map Monday: UCLA Heat Map


Complementing Harvard’s Map of the Month series, Map Monday highlights a data visualization that enhances understanding of or helps resolve a critical civic issue.

Summer 2022 is shaping up to be one of the hottest summers on record, a distinction that seems to be set then surpassed each passing year. According to research from NASA and the National Oceanic and Atmospheric Administration (NOAA), the eight of the top ten hottest years ever recorded on Earth occurred in the last decade, overwhelming evidence of year-over-year heat increases.

Residents of California are not strangers to extreme weather events and environmental disasters, given the frequent wildfires, long droughts, and risk of earthquakes. While not the hottest state in the US, extreme heat coupled with dry climate is a deadly combination. The state government recently released an extreme heat action plan stating that “heat ranks amongst the deadliest of all climate change-driven hazards in California.”  

In an effort to spread information about where extreme heat is occurring, and therefore where government and community resources should be directed, researchers from the University of California Los Angeles (UCLA) developed the UCLA Heat Map. While still in the public beta version, the map provides a granular view of “excess ER visits (number of visits per 10,000 persons per day) due to extreme heat,” which can include emergency room trips for exposure to excessive natural heat, electrolyte imbalance, acute kidney failure and chronic kidney disease, or disorders of fluid, electrolyte, and acid-base balance. The map starts at the county level and can zoom to zip codes to provide a more detailed view. And users can select multiple counties or zip codes to compare data in a graph.

Main Heat Map page with phrase "How Heat Harms Health in Your COmmunity" with map showing Alameda County (571 excess heat-related ER visits)

The ER visits data comes from the California Department of Health Care Access and Information and uses the most up-to-date data available, which is for the year 2009-2018. The map creators plan to update as more data becomes available, and given the year-over-year temperature increases there will likely be even more heat-related emergencies. “Heat event days” are defined by the Spatial Synoptic Classification (SSC) system v.3 which is a common standard for climate and health research. SSC measurements are “based on surface-based observations at an individual station, which includes four-times daily observations of temperature, dew point, wind, pressure, and cloud cover.” These observations occur at weather stations, and there are 67 SSC stations in California according to the researchers. Across the world, many extreme heat warning systems rely on this SSC standard when communicating heat waves and dangers to the public.   

While extreme heat events cause damage across all types of communities, the heat island effect in urban areas results in higher temperatures in denser city environments. Los Angeles County, Alameda County (which includes the city of San Francisco), and San Diego County have the highest number of excessive emergency room visits due to extreme heat.

Map of CA showing that LA had most excess heat ER vists at 1,500+ followed by San Diego (872) and San Francisco (251)

Extreme heat is potentially dangerous for everyone, although the US Centers of Disease Control and Prevention (CDC) states that “small children, the elderly, and certain other groups including people with chronic diseases, low-income populations, and outdoor workers” are at higher risk for heat-related illness like heatstroke. These illnesses (heatstroke, dehydration, sunburn, heat exhaustion) can turn deadly for high-risk populations. According to Kristina Dahl, a senior climate scientist at the Union of Concerned Scientists, “in an average year in the U.S., heat kills more people than any other type of extreme weather.” 

The UCLA team hopes that this map will spur action on the local and community level. For example, neighborhoods can advocate for targeted heat mitigation work by pointing to the harm caused by extreme heat in their community. Hospitals and healthcare workers can also prepare for increased emergency visits and engage in preventative messaging in areas known for extreme heat. Nonprofit and government organizations can most effectively place cooling stations by directing resources at hardest-hit areas. 

Avoiding extreme heat is becoming nearly impossible, with heatwaves covering a vast portion of the globe this summer and temperatures likely to continue rising. Thankfully, maps like this help target attention, care, and prevention to the most vulnerable.

About the Author

Betsy Gardner

Betsy Gardner is the editor of Data-Smart City Solutions and the producer of the Data-Smart City Pod. Prior to joining the Ash Center, Betsy worked in a variety of roles in higher education, focusing on deconstructing racial and gender inequality through research, writing, and facilitation. She also researched government spending and transparency at the Lincoln Institute of Land Policy. Betsy holds a master’s degree in Urban and Regional Policy from Northeastern University, a bachelor’s degree in Art History from Boston University, and a graduate certificate in Digital Storytelling from the Harvard Extension School.