Abstract: To assess quantitatively the impact of climate change on summer precipitation in the Three River Sources (TRS) region, backward trajectory simulations have been conducted using the ERA5 reanalysis data and the Lagrangian particle dispersion model (HYSPLIT). This study focuses on the change in moisture sources within the region in the dry period (2000 to 2002) and wet period (2003 to 2005) of the representative years, and evaluates quantitatively their contributions to the dry-to-wet transition of summer precipitation in the study area. The results reveal that around 2002, the TRS region experienced a significant dry-to-wet transition in summer precipitation. In this region, the southern Tibetan Plateau (TP) emerged as the key moisture source for summer precipitation, because of moisture from the ocean often transiting through the southern TP before reaching it, followed by the contributions from the northern TP and local sources. During wet periods, under the influence of the South Asian monsoon, the southern TP and the Bay of Bengal are the primary moisture sources, contributing 56.4% to the increase in summer precipitation. And under the influence of the westerly belt and northerly winds, the northern TP and Eurasian continent contribute 32.7% to the increase. The results could provide a new perspective for deeper understanding of the dry-to-wet transition of summer precipitation in the TRS region.

Key words: Three Rivers Sources region, summer precipitation, moisture source, moisture transport pathway, water cycle