Spatially explicit humid heat stress projections in urban environments under climate change

Urban areas are centered at the intersection of a changing climate and increasing urban population as drivers of climate change, homes to urban populations and ecosystems, and hubs of potential to mitigate and adapt to climate change. Through their modification of the environment and unique dynamics, urban areas often experience diverse microclimates and enhanced heat stress. Urban modification of the environment has commonly been explored through local and regional studies using air temperature and the urban heat island effect, a phenomenon in which an urban area is hotter than its rural surroundings. Here, I aim to elucidate the impacts of humidity on global patterns of urban humid heat stress and spatially explicit synergies/tradeoffs for adaptation to humid heat. I analyze urban wet-bulb temperatures under future climate change to reveal patterns and drivers of urban humid heat, utilize a spatially explicit population projection to assess future exposure of urban citizens to humid heat, and propose a new metric, Urban Green Infrastructure Potential (UGIP), to assess global patterns of tradeoffs and opportunities for cooling. Results highlight dangerous levels of urban humid heat by the end of the century and a concentration of urban humid heat stress in coastal, equatorial regions. I find that at least 44% of the urban population is projected to be living in an urban area with high TW, JJA. A country-level analysis of the relationship between the percentage of urban land and urban population exposed reveals a strong positive correlation, exposure hotspots, and potential adaptation strategies driven by spatial projections. Finally, I find a tradeoff between UGIP and water availability and that the feasibility and heat mitigation potential of urban green infrastructure is strongly driven by local humidity and water availability. The results presented herein highlight the necessity of global, urban-specific, spatially explicit studies on the impacts of and adaptation to climate change