Impacts of urbanization on summer climate in China: An assessment with coupled land-atmospheric modeling

China has experienced unprecedented urbanization since the 1980s, resulting in substantial climatic effects from local cities to broad regions. Using the Weather Research and Forecasting model dynamically coupled to an urban canopy model, we quantified the summertime climate effects of urban expansion in China's most rapidly urbanizing regions: Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), and Pearl River Delta (PRD). High-resolution landscape data of each urban agglomeration for 1988, 2000, and 2010 were used for simulations. Our results indicated summertime urban warming of 0.85°C for BTH, 0.78°C for YRD, and 0.57°C for PRD, which was substantially greater than previous estimates. Peak summer warming for BTH, YRD, and PRD was 1.5°C, 1°C, and 0.8°C, respectively. In contrast, the loss of moisture was greatest in PRD, with maximum reduction in 2m water vapor mixing ratio close to 1 g/kg, followed by YRD and BTH with local peak humidity deficits reaching 0.8 g/kg and 0.6 g/kg, respectively. Our results were in better agreement with observations than prior studies because of the usage of high-resolution landscape data and the inclusion of key land-atmospheric interactions. Our study also demonstrated that the warming impacts of polycentric urban forms were less intense but more extensive in space, whereas large concentrated urban aggregations produced much stronger but localized warming effects. These findings provide critical knowledge that improves our understanding of urban-atmospheric interactions, with important implications for urban landscape management and planning to alleviate the negative impacts of urban heat islands.