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Dryad

Drivers and projections of global surface temperature anomalies at the local scale

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Jun 09, 2021 version files 39.73 GB

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Abstract

More than half of the world’s population now lives in urban areas, and trends in rural-to-urban migration are expected to continue through the end of the century. Although cities create efficiencies that drive innovation and economic growth, they also alter the local surface energy balance, resulting in urban temperatures that can differ dramatically from surrounding areas. Here we introduce a global 1-km resolution data set of seasonal and diurnal anomalies in urban surface temperatures relative to their rural surroundings and use satellite-observable parameters in a simple model informed by the surface energy balance to understand the dominant drivers of present urban heating, the heat-related impacts of projected future urbanization, and the potential for policies to mitigate those damages. At present, urban populations live in areas with daytime surface summer temperatures that are 3.21°C (-3.97 - 9.24, 5th-95th percentiles) warmer than surrounding rural areas, such that 1.2 billion people are exposed to average surface summer temperatures in excess of 35°C that might put them at risk of heat-related illness. If design and infrastructure of cities remain unchanged, increased urban heat anomalies will add 0.19°C (-0.01, 0.47) to the daytime summer surface temperatures in urban areas in 2100 -- in addition to warming due to climate change. Such urban heating will increase the number of urban population living under extreme and potentially health-threatening temperatures by approximately 20% compared to current numbers. However we also find a significant potential for mitigation: 82% of all urban areas can optimize vegetation and/or surface albedo and reduce urban daytime summer surface temperatures for the affected population on average by -0.81°C (-2.55, -0.05).