Moisture source assessment and the varying characteristics for the Tibetan Plateau precipitation using TRMM

Precipitation over the west Tibetan Plateau (TP) was always being accused of lacking observations that limits the precipitation moisture attribution and quantitation over the whole TP. By introducing precipitation from the Tropical Rainfall Measuring Mission (TRMM) and other observation-based data, moisture sources for the whole TP and their variations from 1998 to 2018 are explored using an Eulerian model. It is found that the Southwest subregion from TP to the western Indian Ocean, is the largest moisture contributor. It contributes around 147.6 ± 13.0 mm yr−1 in water-depth of the TP in climatology, accounting for 31.9 ± 1.9% of the annual precipitation. The TP, the West (TP to Europe), and the Southeast (TP to Indochina Peninsula) follow by contributing 23.6 ± 2.3, 21.8 ± 1.5, and 2.6 ± 0.6%, respectively. Circulations dominate the TP in different seasons. Take spring for example, the westerlies prevail over the TP and the West contributes the most moisture, which accounts for 38.6 ± 2.9% of the spring precipitation. In summer, with the breakout of the Indian monsoon, contribution from the Southwest reaches the highest of 91.1 ± 11.5 mm JJA−1, accounting for 34.6 ± 2.6% of the summer precipitation. The interannual variability (IAV) of the TP precipitation is mainly influenced by the moisture IAVs from the Southwest and the TP, contributing around 36.6% and 31.7%, respectively. Moisture contributed from the Southwest decreases significantly from 1998 to 2018 at a rate of −10.6 mm yr−1 dec−1, but moisture from the local increases significantly at 12.1 mm yr−1 dec−1. Further analyses reveal that the local increase in moisture contribution (and ratio) is primarily due to intensified evaporation of the TP, but the Southwest decrease is mainly caused by reduced moisture transport from the Indian monsoon.