How Does Terrain Relief of the Tibetan Plateau and the Yunnan–Guizhou Plateau Individually Modulate Summer Regional Hourly Extreme Precipitation in the Sichuan Basin, China?

Abstract The influence of terrain relief over the Tibetan Plateau (TP) and the Yunnan–Guizhou Plateau on summer regional hourly extreme precipitation (RHEP) in the Sichuan Basin (SCB) under two dominant synoptic patterns remains poorly understood. Here, this study uses multi‐case Weather Research and Forecasting sensitivity experiments, in which the terrain relief of two plateaus is individually smoothed, to systematically investigate these modulation mechanisms. Terrain relief modulates low‐level flow and moisture, altering thermodynamic and dynamic processes of RHEP under different synoptic patterns. Under P1, featured by a westerly trough and a southwest vortex over western SCB, the terrain relief over the TP (Yunnan–Guizhou Plateau) prolongs the mean RHEP duration by 3.4 hr (0.6 hr) and increases the mean intensity by 0.38 mm hr −1 (0.24 mm hr −1 ) over the western SCB. The prolonged duration and heightened intensity of RHEP are driven by the intensification of the westerly trough and southwest vortex, a process triggered by enhanced atmospheric baroclinicity, low‐level convergence, and vertical‐motion forcing induced by terrain relief. Under P2, characterized by a westerly trough and a southwest vortex over central‐eastern SCB, the terrain relief over the TP prolongs the RHEP duration by 1.3 hr and increases the intensity by 0.07 mm hr −1 over eastern SCB through mechanisms similar to those under P1, but the weakened westerly winds over southeastern SCB limit the enhancement. In contrast, the terrain relief over the Yunnan–Guizhou Plateau reduces the RHEP intensity by 0.32 mm hr −1 via strengthening anomalous northerly winds, blocking southwesterly moisture transport, weakening the westerly trough, and suppressing the southwest vortex.