Urbanization Aggravates Effects of Global Warming on Local Atmospheric Drying

Urbanization is known to cause 'Urban Heat Island' (UHI) and elevate storm runoff. However, how urbanization influences local atmospheric moisture under global warming is not well-understood. By examining 140 paired urban-rural weather station data (1980-2018), this study finds significant declines in atmospheric humidity or the 'Urban Dry Island' (UDI) in multiple large city clusters across a large climatic gradient in China. Global warming, UHI, and reduction in local evapotranspiration and water vapor supplies all contribute to the observed UDI. The magnitude and frequency of UDI are more pronounced in humid regions than arid regions due to differences in background climate and vegetation characteristics that affect both energy and water balances at land surfaces. Mitigating the negative effects of UDI and UHI should focus on restoring the evapotranspiration power of urban ecosystems. The present empirical analyses provide new evidence and mechanistic understanding of environmental change in urban ecosystems.