Amplification Effect of Urbanization on Atmospheric Aridity Over China Under Past Global Warming

While it is well known that rapid urbanization poses prominent effects on regional or local temperature changes under global warming, possible impacts of urbanization on the changes in atmospheric aridity (measured by vapor pressure deficit [VPD]) are poorly understood. In this study, we provide a national investigation of the spatiotemporal changes of atmospheric aridity over China in recent decades by analyzing observations at over 2,000 weather stations across China during 1971-2017 and further quantify the effects of urbanization on the atmospheric aridity changes in different subregions. The results show that most parts of China have experienced a significant intensification of atmospheric aridity since the 1970s. Especially, stronger drying trends tend to appear in urban agglomerations with higher urbanization levels and denser population, such as Beijing-Tianjin-Hebei (BTH), the Yangtze River Delta (YRD), the Pearl River Delta (PRD), and the Sichuan Basin. It is estimated that urbanization contributed to more than 30% of the total increases in atmospheric aridity in urban core areas (i.e., 32.58%, 27.73%, 30.29%, 42.03%, and 37.33%, respectively, for annual, spring, summer, autumn, and winter VPD). Spatially, urbanization exerted significant amplification effects on increasing VPD in most parts of China (nearly 80% grid cells) except for few areas with higher elevation and complex topography (e.g., Qinghai-Tibet Plateau and Xinjiang). In particular, the areas with higher urbanization (e.g., BTH, YRD, and PRD) underwent even stronger urbanization effects on amplifying atmospheric aridity. Our findings suggest that how to alleviate atmospheric aridity in future urban planning is worthy of consideration.