Identifying and contrasting the sources of the water vapor reaching the subregions of the Tibetan Plateau during the wet season

A Lagrangian approach is utilized to identify and compare the sources of water vapor transported to the four subregions of Tibetan Plateau (TP) during the wet season (May-August) of 1980-2016. We focus on the time scale and subseasonal variability of water vapor transport and the relationship between moisture supply and precipitation at the interannual scale. This study finds that: (1) The moisture sources for the four subregions differ significantly in both spatial pattern and magnitude and depend heavily on the combined effects of the summer monsoons, local recycling and the westerlies. (2) The spatial evolution of the moisture sources based on the backward trajectory analysis reveals that, although approximately 80% of the moisture is delivered to the target regions within 1-4 days, the individual subregions feature different transport pathways and associated time scales. (3) The subseasonal migration of the Indian summer monsoon regulates the importance of different moisture sources for the southern TP but not for the northern TP. Additionally, the subseasonal moisture source evolution differs greatly between the southeastern TP and the southwestern TP. (4) The interannual variability of precipitation over the whole TP during summer is negatively correlated with the variation in the moisture transported by the westerlies and is positively related to the moisture conveyed by the Indian summer monsoon for the northern TP and by adjacent moisture transport for the southern TP.