Revisiting the dry-to-wet shift of summer precipitation over the Three-River Headwaters region, hinterland of the Tibetan Plateau: a perspective of moisture sources changes

The Three-Rivers Headwater (TRH) region has experienced notable dry-to-wet shift in summer precipitation in recent decades. Despite the widespread efforts of scientific community, the causes of such climate shift remain not well-understood. Building upon an ensemble of high-resolution Lagrangian simulations and moisture source diagnostic, this study investigated the long-term changes in moisture sources with the ERA-Interim reanalysis from 1980 to 2017, particularly aiming to pose a complimentary understanding on this shift from a perspective of moisture source changes. The results show that the variability of moisture sources for the water vapor reaching the TRH region is closely and quantitatively linked to its regional summer precipitation. The dry-to-wet shift in summer precipitation in TRH is regulated by the changes in moisture sources across multiple transport time scales (from 1 to 10 days), and could be attributed to the enhanced contribution by the moisture sources originated from the Tibetan Plateau (TP), the Central Eastern Asian region (CEA), and the Arabian Peninsula (ARP), of which regional accumulative moisture contribution increased by 11.3 (0.33%), 8.61 (0.27%) and 8.53 (0.52%) mm per year, respectively. This result implies that the terrestrial source ranks the leading role in regulating the decadal shift of TRH summer precipitation, rather than that directly from the oceanic regions. Although the moisture sources are across multiple transport timescales, the relatively shorter transport distance and steady contribution (lasting 1 to 10 days) from the TP highlight the significance of strengthened local precipitation recycling process in this dry-to-wet shift. Further analysis indicates the variations in mid-latitudinal meridional winds and the low-latitudinal SST play a role of ‘bridge’ connecting the changes in moisture sources to enhanced precipitation during the summer season.