Evaluating Neighborhood Environments for Urban Heat Island Analysis and Reduction.

Abstract

City officials are increasingly concerned about heat. Two warming processes are increasing the occurrence of urban heat: 1) global warming caused by greenhouse gas emissions and 2) intensifying urban heat islands (UHI) caused by urbanization. Global climate change increases the frequency, intensity, and duration of hot days. UHIs result in warmer urban air temperatures relative to rural and suburban areas Problems directly resulting from hot weather and UHIs include increased heat mortality, infrastructure failure, increased stress to vegetation, and decreased air and water quality. City officials are increasingly taking action to analyze and reduce UHIs. Yet, past research provides insufficient information for researchers and planners on 1) the relative contribution of neighborhood physical characteristics to UHIs and how those physical characteristics’ contribution may change during different times of day, 2) the accuracy of land cover quantification necessary to predict UHIs, and 3)monitoring the performance of in-situ cool pavement strategies. To address these gaps in the literature, I conducted three related studies of UHIs in eight Chicago neighborhoods in 2010. 1) I found that light winds at night resulted in stronger relationships between independent neighborhood physical variables and UHI intensity (2 a.m., adjusted R2 = 0.68) than during the afternoon (4 p.m., adjusted R2 = 0.26). At night land cover variables were better predictors of UHIs relative to other factors. Yet, during the afternoon, I found that upwind heat sources were better predictors of UHIs relative to other factors. 2) In the second study, I found that coarse (two-dimensional) quantification of impervious surface area are sufficient for UHI prediction. Even so, more detailed (three-dimensional) quantification that document impervious surfaces concealed by tree canopy are likely better for urban forestry and planning for rights-of-way. 3) Finally, I found that out of six different cool pavement strategies, highly reflective concrete and pervious concrete, cooled the air. Both designs had cooler air at three meters by at least -0.40⁰C compared to conventional asphalt paving. As city officials move to implement initiatives to reduce UHIs, this research provides a useful direction on how to conduct UHI analysis and monitor the performance of UHI reduction strategies.