Heat Vulnerability and Cooling Opportunities

The expansion and densification of cities change the existing landscapes in ways that significantly alter ecosystems of all scales. Expansion of roads, parking lots, and built structures have increased impermeable surface areas, causing an increase in surface temperatures, a phenomena referred to as the urban heat island. The mechanics of the consequential relationship between urbanization and increased surface temperatures have been well documented in public health and environmental research. This report contributes to the present body of research by providing a framework through which thoughtful planning efforts to reduce the urban heat island (UHI) can be developed. Specifically, this report unpacks the processes and results of a spatial analysis that identifies geographies within the City of San Diego that are in particular need of cooling efforts. The spatial analysis consists of heat exposure information derived from land surface temperature data from NASA’s Landsat 8 satellite, and heat sensitivity information derived from population data from the United States Census Bureau. The spatial analysis is then leveraged in the creation of a decision map that compares census tracts within San Diego according to their relative heat vulnerability. This decision map is advanced further in order to evaluate the expected productivity of various cooling strategies in the target census tracts. In addition to a discussion of the findings and applications of the cooling strategies advocated, this report makes specific recommendations as to which strategies should be pursued in which geographies. The majority of the most heat vulnerable census tracts are within the Mid-City and Southeastern neighborhoods of San Diego. 24 of these census tracts were identified as ones for which cooling efforts would be most impactful. These census tracts were determined through an evolution of the heat vulnerability decision map, which captured population size. Recommendations for each census tract were developed through a consideration of their individual attributes in relation to the most popular and proven cooling strategies. The analysis led to tailored recommendations of special efforts to expand existing tree canopies in 10 of the 24 target census tracts, to increase the amount of park space in 7 of the 24 census tracts, and to establish 4 new cooling centers within walking distance of the 5 of the 24 census tracts that currently lack remote cooling centers. Additional cooling tools, including cool roofs, green roofs, and cool pavement were also advocated for. Estimated impact, cost-benefit analysis, and strategies for implementation of all of the recommended cool techniques, including zoning incentives, grants, and demonstration projects, is discussed.