CalEPA’s Urban Heat Island Interactive Maps

CalEPA’s Urban Heat Island Interactive Maps: The California Environmental Protection Agency has released an interactive urban heat map tool that shows heat islands throughout the state of California. Using Google Earth, the tool color codes the heat of cities according to intensity, with green at the lowest temperatures, and red at the highest. Temperatures were taken over the summer of two years—2006 and 2013. One of the outputs the map provides is an urban heat index, which quantifies the extent and severity of an urban heat island in a particular area within a city. Users can download the tool and corresponding data set to determine what areas of a City have a higher heat intensity, and how many people live in that area.

Once the map is open, the user can click on urban areas to view the urban heat island effect by census tract. The Urban Heat Island Index is calculated as a temperature differential over time between an urban census tract and nearby upwind rural reference points at a height of two meters above ground level, where people experience heat. Temperature differences every hour for every day across two summers are added up and divided by 182, to give the heat island effect calculated in degree-hours per day — a measure of heat intensity over time. Accordingly, the interactive map labels the urban heat island index as “DegHourDay,” displayed when the user clicks on a census tract.

Related Organizations:

  • California Environmental Protection Agency (CalEPA)


Resource Category:

Resource Types:

  • Modeling tool

States Affected:


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