How Lateral Flow Impacts Heavy Rainfall in Complex Terrain: A Composite Analysis Over the Southern Anhui Mountainous Region

Abstract High‐resolution modeling of terrestrial hydrological processes offers new opportunities to advance the understanding of land‐atmosphere (L‐A) interactions. To investigate the impact of soil lateral flow (LF) on heavy rainfall events in mountainous areas of the Yangtze‐Huai region, we conducted two sets of convection‐permitting WRF simulations over eastern China for three summers, that is, a standard WRF run without LF effect (WRF‐S) and a fully coupled WRF/WRF‐Hydro simulation with LF process turned on (WRF‐H). With simulation results for three summers, total 13 heavy rainfall events can be identified over the southern Anhui mountainous (SAM) region in both observation and model simulations. Based on the precipitation differences between WRF‐H and WRF‐S in the SAM region, the above heavy rainfall events were further categorized into seven positive‐effect events, in which LF led to increased precipitation, and oppositely six negative‐effect events. Composite analysis of positive‐effect events reveals that LF increases soil moisture (SM), particularly in valley areas. This intensifies evapotranspiration (ET) and increases convective available potential energy (CAPE) through L‐A interaction, demonstrating an LF‐triggered “SM–ET–CAPE” pathway that enhances precipitation over the SAM region. During negative‐effect events, rainfall was largely enhanced in the Yangtze Plain, which is to the southwest of SAM. The rainfall‐induced suppression of ET over the Yangtze Plain reduced CAPE, thereby inhibiting the “SM–ET–CAPE” pathway. This research quantifies the impacts of LF on land surface processes and contributes to a better understanding of L‐A interactions, particularly the effects of LF on heavy rainfall in the SAM region.