A three-dimensional WRF-based precipitation equation and its application in the analysis of roles of surface evaporation in a torrential rainfall event

• Precipitation equation was extended from 2D model framework into 3D WRF model framework.
• Roles of moisture and cloud-related processes in a torrential rain event were studied.
• Roles of surface evaporation were significant in the short-term heavy rain event over land.

Based on the governing equations for water species in the Weather Research and Forecasting (WRF) model, a three-dimensional WRF-based surface precipitation equation was obtained and applied to investigate the surface rainfall processes of a torrential rain event. Sensitivity experiments were performed to further explore roles of surface evaporation in the heavy rainfall event. The results show that the contributions of moisture-related processes to precipitation (QWV, including water vapor local change (QWVL), surface evaporation (QWVE), moisture advection (QWVA), and so on) dominate the torrential rain event, while the contributions of cloud-related processes (QCM) also play indispensable roles whose maximum net contributions could exceed 20%. QWVA dominates the budget of water vapor, while QWVL and QWVE play smaller but by no means negligible roles in the event. Sensitivity experiments show that the changes of surface evaporation affect both moisture-related processes and cloud-related processes, and then influence the intensity and regional redistribution of precipitation. Surface evaporation favors the accumulation of convective available potential energy and enhances the instability of atmosphere, being prone to the development of convective systems. Meanwhile, it also affects the development of vertical motions and cloud systems. Thus accurate estimation of surface evaporation is necessary for accurate simulation and forecast of surface precipitation.