Analysis of Multi-Scale Characteristics of Plateau Precipitation under the Influence of Bay of Bengal Storms

Based on hourly precipitation data from Chinese automatic weather stations (2000-2020), this study employs the REOF method to classify plateau precipitation into three regions: Central and Eastern Tibet, Central Qinghai, and Northwestern Yunnan (Region I); Western Tibet, Western Qinghai, and Northern Gansu (Region II); and Southeastern Qinghai and the Western Sichuan Plateau (Region III). Plateau precipitation generally decreases from east to west, with Region I exhibiting the earliest peak and Region III the latest. Hourly extreme precipitation amounts and frequencies both show an "east-high, west-low" pattern, and frequencies of heavy rainfall is higher at the southeastern plateau, the rain intensity is stronger at the northeastern plateau. The peak time of hourly heavy precipitation in Region III is the earliest. Under the Bay of Bengal (BOB) storm influence, heavy precipitation concentrates in the northeastern and southern plateau, and the high-frequency zone is located in the southeastern plateau. The precipitation peaks occur from afternoon to night, and the peak time in Region III is the earliest, showing a distinct east-to-west delay. The peak time of the average rain intensity is earlier than the peak time of the number of the stations exceeding four precipitation thresholds, which means that extreme heavy rainfall occurs more frequently in the afternoon, while widespread heavy precipitation favors night. In Region III, the frequency peaks exceeding four precipitation thresholds occurs around 2100-2200 LST, indicating heavy rainfall induced by the BOB storm favors night in this area. The maximum contribution rates of the BOB storm-related hourly heavy precipitation are distributed over the eastern and southern plateau, with the 90th percentile precipitation contribution rate exceeding 60%, highlighting the prominence of short-duration heavy rainfall. Complex topography in the eastern and southern plateau characterized by valleys and intersecting terrain enhances convergence and uplift of warm, moist airflows from northward-moving BOB storms, further facilitating heavy precipitation generation.