Understanding the impact of urban expansion and lake shrinkage on summer climate and human thermal comfort in a land-water mosaic area

Wuhan has witnessed unprecedented urban expansion that encroached upon sizable inland lakes. However, the impacts of urban expansion on climate and heat stress for such a city with complex physiographic background (land-water mosaics) remain understudied. Using a coupled urban-lake-atmospheric model, we first examined summer climate responses to urban expansion and lake shrinkage in Wuhan during 2000-2020. Second, multiple heat stress indicators were used to evaluate human thermal comfort in different contexts of interest. Results showed that the presence of water bodies reduced daytime maximum temperature, raised nighttime minimum temperature, and increased moisture content in urban and built-up areas. Urban expansion alone led to summer warming of 0.9 degrees C and drying of 0.9 g/kg, with local peak warming and drying up to 2 degrees C and 1.4 g/kg. In comparison, urban expansion with lake shrinkage showed a reduced magnitude of warming of 0.8 degrees C and increased magnitude of drying of 1.6 g/kg, with the maximum changes up to 1.4 degrees C and 2.0 g/kg. The presence of water bodies reduced while urban expansion increased the frequency of occurrence of yellow and orange heat alert days; however, both increased the number of days exerting high thermal risks on outdoor workers and those days that were dangerous for outdoor pedestrians. Our study underlined that both urban expansion and water body existence exerted a strong influence on summer climate and heat stress in Wuhan, and highlighted that mitigation measures should be taken to alleviate the deleterious impacts of high temperature and humidity on human health.