Evaluation of Different Urban Canopy Schemes in Simulating a Heatwave and Urban Heat Island over North China

Urbanization significantly affects regional climate, and accurately representing urban canopy processes is crucial for simulating heatwaves in highly urbanized regions such as North China. To evaluate the impacts of different urban canopy schemes on surface parameter simulation, this study compares the No Urban Canopy Model (NOUCM), Single-Layer Urban Canopy Model (SLUCM), and Multi-Layer Urban Canopy Model (MLUCM) during a heatwave in North China from 5 to 7 July 2023. The simulations use WRFv4.6.1 and are verified against observations from 141 urban stations. NOUCM shows a positive bias in 10 m wind speed. SLUCM introduces a building drag effect, but its single-layer representation cannot resolve the vertical distribution of drag, leading to a 15.8% increase in RMSE relative to NOUCM. MLUCM explicitly represents the building drag effect and reduces RMSE by 29.5%. For 2 m temperature, all schemes show positive biases. SLUCM produces cooler daytime and warmer nighttime temperatures, with a large nighttime bias. MLUCM more realistically simulates shading and radiation trapping, reducing the daytime RMSE by 18.2% and yielding nighttime biases close to zero. For 2 m specific humidity, SLUCM and MLUCM reduce RMSE by 1.8% and 0.7%, respectively. For urban heat island (UHI) intensity, MLUCM achieves an overall RMSE of 0.721 °C, which is 30.2% and 33.2% lower than NOUCM and SLUCM, respectively. It also produces the smallest daytime and nighttime biases, with good agreement with observations during 12–20 h. SLUCM shows a nighttime UHI bias of +1.094 °C, while NOUCM shows a daytime bias of +1.176 °C. Overall, MLUCM demonstrates superior performance in simulating wind speed, temperature, and UHI intensity, though its advantage in 2 m specific humidity is limited. These findings provide a reference for selecting urban canopy schemes in operational numerical weather prediction over highly urbanized regions.