{"id":768878,"date":"2025-10-28T19:50:47","date_gmt":"2025-10-29T02:50:47","guid":{"rendered":"https:\/\/www.esri.com\/about\/newsroom\/?post_type=arcnews&p=768878"},"modified":"2025-10-28T19:50:47","modified_gmt":"2025-10-29T02:50:47","slug":"california-leads-the-way-in-preparing-for-extreme-heat","status":"publish","type":"arcnews","link":"https:\/\/www.esri.com\/about\/newsroom\/arcnews\/california-leads-the-way-in-preparing-for-extreme-heat","title":{"rendered":"California Leads the Way in Preparing for Extreme Heat"},"author":5752,"featured_media":0,"menu_order":0,"template":"","format":"standard","meta":{"_acf_changed":false,"sync_status":"","episode_type":"","audio_file":"","podmotor_file_id":"","podmotor_episode_id":"","castos_file_data":"","cover_image":"","cover_image_id":"","duration":"","filesize":"","filesize_raw":"","date_recorded":"","explicit":"","block":"","itunes_episode_number":"","itunes_title":"","itunes_season_number":"","itunes_episode_type":"","_links_to":"","_links_to_target":""},"categories":[472991,91,211],"tags":[425592,163382,482212,160522,170182],"arcnews_issues":[493219],"class_list":["post-768878","arcnews","type-arcnews","status-publish","format-standard","hentry","category-gis","category-mapping","category-public-safety","tag-arcgis-experience-builder","tag-arcgis-online","tag-extreme-heat","tag-health","tag-risk","arcnews_issues-fall-2025","arcnews_sections-news"],"acf":{"short_description":"CalHeatScore\u2014a first-of-its-kind system\u2014ranks heat risk on a scale from 0 to 4 at the ZIP code level, helping people know when it\u2019s too hot.","pdf":{"host_remotely":false,"file":"","file_url":""},"flexible_content":[{"acf_fc_layout":"content","content":"When warm temperatures rise above average levels, especially for several days or weeks in a row, the consequences can be dire. In September 2022, a 10-day heat wave in California brought temperatures of 109 degrees Fahrenheit to Long Beach and 116 degrees to Sacramento, killing 395 people, according to state health officials.\r\n\r\n\u201cExtreme heat kills more people than any other climate hazard combined\u2014more than wildfire, more than hurricanes,\u201d said Walker Wieland, environmental program manager for California\u2019s Office of Environmental Health Hazard Assessment (OEHHA). \u201cBut extreme heat doesn\u2019t have eye-catching graphics or images to make people aware of its dangers.\u201d"},{"acf_fc_layout":"image","image":768879,"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"During extreme heat events, more people get sick, and some die. Yet, according to Wieland, public awareness of extreme heat\u2019s dangers\u2014and what to do when it strikes\u2014remains low.\r\n\r\n\u201cA lot of people just think, \u2018I\u2019m going to tough it out. I\u2019ve felt heat like this in the past, so I\u2019m just going to continue with all my planned activities for the day,\u2019\u201d he said. \u201cBut that can have really dangerous and sometimes deadly consequences.\u201d\r\n\r\nTo help people across California prepare for and stay safe during extreme heat events, Wieland and his team developed CalHeatScore<\/a>, a first-of-its-kind system that ranks heat risk on a scale from 0 to 4 at the ZIP code level. The online tool, built in ArcGIS Experience Builder, includes a map that divides the state into ZIP codes and shades each one a color ranging from light gray (low risk) to deep red (severe risk), depending on forecasted heat impacts for the current week. A tab displays cooling centers, such as libraries and community centers where people can access air conditioning and hydration. The tool also provides information on why each area has its heat ranking, along with profiles of the population\u2019s age ranges, race and ethnicity breakdowns, access to health insurance, number of outdoor workers, and more.\r\n\r\n\u201cThe tool is unique in its granularity,\u201d said Dr. Amy Gilson, OEHHA\u2019s deputy director for external and legislative affairs. \u201cGetting down to the ZIP code level is key in California because we have a lot of microclimates. It\u2019s also integrated with public health data, so CalHeatScore is well-positioned for individuals and local decision-makers to use.\u201d"},{"acf_fc_layout":"image","image":768880,"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"\u201cWe\u2019re trying to make it as easy as possible for people to get a sense of what heat conditions and risks are like,\u201d Wieland added."},{"acf_fc_layout":"content","content":"

How CalHeatScore Works<\/h2>\r\nCalHeatScore, which launched at the end of 2024 and ramped up as temperatures began rising this May, was inspired by existing warning systems, such as those for hurricanes and tropical storms. The team wanted the system to communicate different risk levels without being overwhelming, so it adopted the 0\u20134 ranking system to convey low, mild, moderate, high, and severe heat risks.\r\n\r\nTo get weather and forecast data, the team relies on the National Oceanic and Atmospheric Administration\u2019s National Digital Forecast Database, which uses data from regional Weather Forecast Offices and satellites to provide forecasts and weather models for the entire United States, broken down into a 2.5-kilometer grid. CalHeatScore then compares this weather data to historical climate conditions across the state to determine whether temperatures are below, at, or above average.\r\n\r\nCrucially, CalHeatScore also analyzes emergency department visit data and compares those numbers with average climate conditions. This helps form statistical relationships between climate conditions and health impacts. When temperature forecasts rise, CalHeatScore reports expected increases in emergency department visits, serving as a measure for community health risk. With this information, CalHeatScore can model when temperatures in specific areas may become too hot for people to tolerate."},{"acf_fc_layout":"gallery","gallery_images":[768881,768882]},{"acf_fc_layout":"content","content":"\u201cThis combination of fine-scale climate and weather information along with emergency department data allows us to tell more granular stories of heat and health for every community across the state,\u201d said Wieland.\r\n\r\nFor example, in Redlands\u2014a valley community known for being hot and dry\u2014it could be 95 degrees. If that aligns with the average temperature for that time of year, and emergency room visits don\u2019t spike at that temperature, CalHeatScore would give Redlands ZIP codes a risk level of 0 (low) or 1 (mild). But on the same day in Forest Falls\u2014a mountain community less than 20 miles away from Redlands\u2014it could be 82 degrees. If the data shows that the average temperature around this time is usually lower, and emergency room visits increase when it\u2019s 82 degrees outside, Forest Falls could receive a risk level of 3 (high) or 4 (severe).\r\n\r\nTo help people know what to do during extreme heat events, Wieland and his team work with local community organizations to share details about cooling centers. CalHeatScore, available in English and Spanish, also contains information on signs of heat illness and how to stay cool.\r\n\r\n\u201cCalHeatScore is a tool that Californians can use to understand heat risk, plan ahead, and keep themselves and their loved ones safe from extreme heat,\u201d said Wieland.\r\n\r\nHow it works is all the data\u2014the weather forecasts acquired every 24 hours, the historical climate data, and the emergency department visitation rates\u2014is pulled together in Python. The Python script runs at midnight and 5:00 a.m. every day, calculating the increased risk of emergency department visits for each ZIP code. That value is then translated into CalHeatScore\u2019s 0\u20134 ranking system, with 0 meaning there is no risk for the ZIP code and 4 meaning there is an expected 100 percent (or more) increase in emergency department visitation rates."},{"acf_fc_layout":"image","image":768883,"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"This information is updated in ArcGIS Pro as a feature layer, which is automatically pushed to ArcGIS Online. The feature layer sits in a stylized web map and is displayed alongside other data, including a map of cooling centers and dashboards that show population information, such as vulnerable groups in each ZIP code. All this is made available to the public online via Experience Builder.\r\n\r\n\u201cWith Experience Builder, we\u2019re able to design and put out straightforward messaging, like information about workers\u2019 rights and recognizing the signs of heat-related illness,\u201d said Wieland. \u201cExperience Builder allows us to add educational materials to our scientific data and makes it easy to adjust how we present that information.\u201d"},{"acf_fc_layout":"content","content":"

Making the Tool More Granular<\/h2>\r\nWieland and his team are still in the early stages of creating CalHeatScore and are committed to developing it transparently, alongside local community organizations."},{"acf_fc_layout":"image","image":768884,"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"\u201cThere are so many new directions that we could go to make this tool more comprehensive, more characteristic of on-the-ground or lived experiences, and more customized by building it in partnership with state and local government and community organizations,\u201d Wieland said.\r\n\r\nOne idea the team wants to pursue is making CalHeatScore interoperable with other systems, including mobile apps, by developing application program interfaces (APIs).\r\n\r\n\u201cHaving a tool that communicates risks for heat is so much more valuable to have on your phone than just having it on your desktop,\u201d he said. \u201cOne of the key benefits that you could potentially get using a mobile app is notifications.\u201d\r\n\r\nThe idea is to allow users to build a profile in CalHeatScore, where they could input their demographic information, health status, occupation, and more. Then the system could send them customized notifications based on who they are, where they are, and the day\u2019s conditions.\r\n\r\n\u201cIf you\u2019re an older adult who works outside for a living, for example, the inherent risks of you becoming ill from extreme heat are higher than those of a young individual working indoors who has no pre-existing conditions,\u201d Wieland explained. \u201cIf the system knows that you have an increased sensitivity to heat, it could provide you with more targeted messaging. So if it\u2019s 82 degrees, and you\u2019re a young, healthy individual, maybe the score you receive for that day is 0. But if you\u2019re 75 years old, have asthma, and are working outside, maybe you receive a higher rating.\u201d"},{"acf_fc_layout":"image","image":768885,"image_position":"center","orientation":"horizontal","hyperlink":""},{"acf_fc_layout":"content","content":"Another idea is to overlay the CalHeatScore data with air quality index and smoke plume data to better understand how air pollution and particulates affect public health during extreme heat. The team is also developing a data download portal where users can access historical CalHeatScore data for their own research. By next summer, the team hopes to increase the spatial resolution of its heat data\u2014by considering urban heat island effects and localized rural heat, especially in agricultural areas\u2014and expand the heat-related health issues that the tool addresses to include long-term impacts and mortality data.\r\n\r\n\u201cOnce we come into heat season in 2026, we\u2019re hoping to release an updated version of the tool that has a higher spatial resolution and a more comprehensive picture of what this relationship between heat and health looks like,\u201d Wieland said.\r\n\r\nTo ensure that the tool is accurate for users everywhere, the team will continue to work with other state agencies, county and city governments, and local community organizations. It also welcomes ideas from California residents and the GIS community on how to improve CalHeatScore.\r\n\r\n\u201cWe\u2019ll continue building on the tool to make sure it\u2019s based on people\u2019s experience on the ground,\u201d Gilson said.\r\n\r\nFor more information about CalHeatScore or to get in touch with the team, email Wieland at walker.wieland@oehha.ca.gov<\/a>."}],"references":null},"yoast_head":"\nCalifornia Leads the Way in Preparing for Extreme Heat | Fall 2025 | ArcNews<\/title>\n<meta name=\"description\" content=\"CalHeatScore\u2014a first-of-its-kind system\u2014ranks heat risk on a scale from 0 to 4 at the ZIP code level, helping people know when it\u2019s too hot.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.esri.com\/about\/newsroom\/arcnews\/california-leads-the-way-in-preparing-for-extreme-heat\" \/>\n<meta property=\"og:locale\" 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