Creating and mapping an urban heat island index for California







In order to further evaluate the factors that can influence thermal environmental stresses, a characterization of how urban areas affect local microclimates, air temperature in particular, is necessary. To assist the CalEPA in evaluating the thermal impacts of urban areas in California, this study characterizes the urban heat island (UHI) and quantifies an urban heat island index (UHII) for each census tract in a number of urban areas. For this purpose, detailed multi-scale meteorological modeling was carried out and a UHII definition was developed. The analysis indicates that the UHI can be exacerbated during warmer weather and that, in turn, can exacerbate the health impacts of heat events in urban areas. Along with other available environmental data, such as from CalEnviroScreen or other region-specific assessments, the UHII can provide information to help identify and prioritize areas for mitigation. This study does not propose mitigation measures or suggest certain control strategies, nor does it assess their potential effectiveness or positive and negative impacts; it only is a characterization of the UHI and UHII in various urban areas in California under existing conditions. This is a state-funded research study sponsored by Cal EPA.

Climate Impact Tags

Extreme heat Temperature

Adaptation Planning Guide Phases

Phase 2: Assess Vulnerability

Resource Type Tags

Scientific study


Extent: California


Last updated: May 21, 2024