Roles of the Tibetan Plateau and Yunnan‐Guizhou Plateau in the Regional Extreme Precipitation Over Sichuan Basin in Summer: A Case Study

Abstract

AbstractThe roles of the Tibetan Plateau (TP) and Yunnan‐Guizhou Plateau (YGP) in regional precipitation extremes over the Sichuan Basin (SCB) in summer under specific circulation background remain unclear. This study quantifies the impact of TP or YGP on the regional extreme precipitation event (REPE) which occurred during 04:00 Beijing time (BJT) on 11 August to 03:00 BJT on 13 August 2020 with a rainfall center located in the western SCB based on numerical experiments. Results show that the accumulated precipitation regionally averaged over the western SCB during the REPE can be reduced by 84% (51%) when the TP (YGP) is absent, and the decreased precipitation is mainly caused by the reduced stratus precipitation. Mechanism analysis indicates that relative to the control experiment including the TP and YGP, the absence of TP or YGP leads to reduced temperature over the SCB induced by anomalous cold advection from the upstream regions where the terrains are removed, and further results in much more stable stratification and thereafter weakens the ascending motions and reduces the stratus precipitation over the western SCB. On the other hand, the absence of TP or YGP induces an anomalous anti‐cyclone at 850 hPa over SCB, which further weakens both the uplift effect of terrain on airflow along the windward slope and water vapor transport over the western SCB and thereafter reduces the precipitation over this region. This study deepens the understanding of the topographic effect on regional extreme precipitation over SCB in summer from the thermodynamic and dynamic processes.