Factors that Explain Urban Heat Islands in Chicago

By Paul Coseo and Larissa Larsen

Chicago, IL (May 2014) – New research to be published in the May 2014 issue of Urban and Landscape Planning, combined 14 physical measures to estimate elevated air temperatures in eight Chicago neighborhoods. The study, “How factors of land use/land cover, building configuration, and adjacent heat sources and sinks explain Urban Heat Islands in Chicago, ” combined variables from the remote sensing and urban climatology publications to explain Urban Heat Island intensity.

Urban Heat Islands are urban and suburban areas with elevated surface and air temperatures relative to surrounding rural areas. During the summer of 2010, researchers collected air temperature measurements within an urban block in each neighborhood. Consistent with remote sensing research that measures surface temperature, the predictors of elevated nighttime air temperatures were land cover variables.

At 2 a.m., the urban block’s percentages of impervious surface and tree canopy explained 68% of the variation in air temperature. At 2 a.m., the other physical measures of urban canyon and street orientation were not significant. At 2 a.m. during extreme heat events, the urban block’s percentages of impervious surface and tree canopy explained 91% of the variation in air temperature.

At 4 p.m., the only significant explanatory variable was distance to industrial sites and this explained 26% of the variation in air temperature. At 4 p.m. during extreme heat events, there were no significant predictors.

Research findings illustrate the importance of differentiating time of day for residential and non-residential areas in UHI mitigation efforts and the need to include waste heat in future UHI investigations. It also shows the impact of the amount of impervious surfaces and tree canopy on air temperature variations.