Diurnal interaction between urban expansion, climate change and adaptation in US cities

Climate change and urban development are projected to substantially warm US cities, yet dynamic interaction between these two drivers of urban heat may modify the warming. Here, we show that business-as-usual GHG-induced warming and corresponding urban expansion would interact nonlinearly, reducing summer night-time warming by 0.5 K over the twenty-first century in most US regions. Nevertheless, large projected warming remains, particularly at night when the degree of urban expansion warming approaches that of climate change. Joint, high-intensity implementation of adaptation strategies, including cool and evaporative roofs and street trees, decreases projected daytime mean and extreme heat, but region- and emissions scenario-dependent nocturnal warming of 2–7 K persists. A novel adaptation strategy—lightweight urban materials—yields ~1 K night-time cooling and minor daytime warming in denser areas. Our findings highlight the diurnal interplay of urban warming and adaptation cooling, and underscore the inability of infrastructure-based adaptation to offset projected night-time warming, and the consequent necessity for simultaneous emissions reductions.