Characterizing surface and canopy urban heat islands and impacts of land use and land cover change in a third-pole city

This study investigated the summer urban heat island (UHI) effects in Xining, a typical valley city on the Tibetan Plateau (TP), using the Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model. Two groups of WRF simulations were conducted to explore the temporal variations of surface and canopy UHI (SUHI and CUHI) effects in July over past several decades, as well as the impact of land use and land cover change (LULCC) on UHIs. Results indicate a continuous enhancement of both SUHI and CUHI effects with urban expansion, nearly tripling from 1994 to 2018. At the diurnal scale, SUHI peaks before sunset due to surface energy balance processes, while CUHI peaks after sunset, influenced by the boundary layer development. LULCC plays an important role in intensifying the UHI effects, contributing more than 60 % by 2018. The amplified UHI effects driven by the LULCC strengthen local near-surface winds by modulating the mountain-valley wind patterns, further in turn enhancing UHI effects and creating a self-reinforcing mechanism. This paper provides an improved understanding of urban effects in high-altitude cities and establishes a strong foundation for further research on improving the urban environment and promoting sustainable urban development in the TP.