Influence of urban rooftop photovoltaic deployment on thermal environment during a heatwave event in complex terrain

• Cooling effect: RPVPs lower urban temperatures day and night, with stronger cooling in eastern (day) and central (night) areas. • UHI mitigation: Increasing RPVP coverage (25 %–100 %) weakens UHI intensity, achieving a maximum reduction of 0.71 K in the afternoon. • UDI alleviation: RPVPs notably diminish the urban dry island effect, particularly between 14:00–18:00. • Improved thermal comfort: RPVPs lower the heat index during peak heat, benefiting eastern and southern urban areas most. • Climate adaptation: Demonstrates RPVPs’ potential as a sustainable strategy for complex terrain cities in arid/semi-arid regions. This study investigates the influence of rooftop photovoltaic panels (RPVPs) on the thermal environment during a heatwave event in Lanzhou, a complex terrain city in China. Using the Weather Research and Forecasting (WRF) model coupled with the Building Effect Parameterization and Building Energy Model (BEP + BEM), we simulate the impacts of RPVPs with varying coverage rates (25 %, 50 %, 75 %, and 100 %) on near-surface temperature, urban heat island (UHI) effect, urban dry island (UDI) effect, and human thermal comfort. The results demonstrate that RPVPs reduce urban temperatures during both daytime and nighttime, exhibiting a more pronounced cooling effect in the eastern part of the city throughout the daytime and in the central area during nighttime. As the coverage rate of RPVPs increases, the UHI intensity (UHII) is significantly mitigated, particularly in the afternoon, with a maximum reduction of 0.71 K. Furthermore, RPVPs also alleviate the UDI effect, especially between 14:00 and 18:00. Finally, RPVPs improve human thermal comfort by lowering the heat index (HI) during peak heat periods, with the more significant benefits in the eastern and southern urban areas. This study highlights the potential of RPVPs as an effective urban climate mitigation strategy in complex terrain cities, providing scientific insights for sustainable urban development in arid and semi-arid regions.