Urban irrigation reduces moist heat stress in Beijing, China

Although urban irrigation can modulate local hydrothermal conditions and mitigate urban heat island effects, its impact on moist heat stress (MHS) is poorly understood. Employing the Weather Research and Forecasting Single-Layer Urban Canopy Model (WRF-SLUCM), we evaluated the effect of urban irrigation on MHS in Beijing, China, and found that the updated initial soil moisture field improved the simulation of temperature, relative humidity, and wind speed. Urban irrigation reduced urban and rural MHS, particularly reducing afternoon and evening MHS by up to 1.2 °C but increasing morning MHS by up to 0.4 °C. Different irrigation times had distinct impacts: irrigation at 02 and 20 UTC increased urban and rural MHS, while the best cooling occurred at 00 and 13 UTC, reducing MHS by up to 2.65 °C in urban areas and 0.71 °C in rural areas. The findings highlight mechanistically the effect of urban irrigation on MHS and provide insights for mitigating urban heat island effects to support urban sustainable development.