Summer Extreme Precipitation in the Key Region of the Sichuan-Tibet Railway

The Sichuan-Tibet Railway, mainly located in the southeastern Qinghai-Tibet Plateau, is affected by summertime extreme precipitation (SEP). Using daily rain-gauge observations and ERA5 reanalysis data for the summers of 1979–2020, the spatiotemporal distribution characteristics of SEP in the key region of the Sichuan-Tibet Railway (28°–33°N, 90°–105°E, hereafter KR) are revealed, and the mechanism for SEP amount (SEPA) variation in the KR is investigated. The results show that SEPA in the KR contributes nearly 30% to the total summer precipitation. Regional differences are evident in SEP, justifying thresholds higher in the plateau-dominated central-western KR (CWKR) and lower in the basin-dominated eastern KR (EKR). In addition, SEP in the CWKR is less intense but more frequent than SEP in the EKR. During 1979–2020, the SEPA in the KR increased slightly while the SEPA in the CWKR increased significantly and peaked in the last decade. When anticyclonic circulation (AC) anomalies dominate the 500 hPa pattern over the Bay of Bengal and Mongolia, the southerly flow and cyclonic shear over the southeastern plateau will be strengthened, favoring more SEPA in the CWKR. When an AC anomaly dominates the 500 hPa pattern over the Bohai Sea, the low-level easterly wind over the basin will be strengthened, favoring more SEPA in the EKR. The strengthening of the ascent, water vapor convergence, and convective instability is conducive to more SEPA in the KR. Our results deepen the understanding of the characteristics and the physical mechanisms responsible for extreme precipitation in the KR.