Impact of Large-Scale Topography Surrounding the Sichuan Basin on Its Regional Hourly Extreme Precipitation in Summer Under Specific Weather Patterns: Multi-Case Study

The influence mechanism of large-scale topography surrounding the Sichuan Basin (SCB) on its precipitation under two dominant weather patterns that typically trigger the regional hourly extreme precipitation events (RHEPEs) in summer remains unclear. Based on multi-case simulations, this study revealed how the Tibetan Plateau (TP) and Yunnan–Guizhou Plateau (YGP) affect the precipitation over SCB under different dominant weather patterns of RHEPEs in summer through sensitivity experiments. Results show that under the weather pattern featured by a low-level vortex (LLV) over western SCB with water vapor transport by southerly winds, the YGP and TP can increase the precipitation in western SCB by 86% and 46%, respectively. The large-scale terrains of TP and YGP tend to enhance the thermal gradient between the plateau and basin and shape the windward slope over western SCB, accounting for increased precipitation there. Under the weather pattern featured by a LLV over central and eastern SCB with southwesterly winds, the TP can only increase the precipitation in the eastern SCB by 20% due to its limited effects on the atmospheric circulations along the windward slope there, however, the YGP can decrease the precipitation in eastern SCB by 26%, which is attributed to the anomalous northeasterly winds weakening the water vapor transport from the Bay of Bengal, leading to the strengthened stability of stratification and weakened dynamic uplifting along the windward slope in eastern SCB. Finding of this study provides a new perspective on the mechanisms of large-scale terrain influencing the RHEPEs over SCB.