Spatiotemporal variations of precipitation during the rainy season over the three-rivers headwater region of tibetan plateau from 1990 to 2020

The Three-River Headwater Region (TRHR) has undergone significant hydrological changes and affects the water resources security in the local and downstream areas. We use multiple observational precipitation product, as well as the ERA5 reanalysis dataset to investigate the precipitation variations over the TRHR during the rainy season from 1990 to 2020, and to analyze the contributions of local evaporation and remote water vapor transport to the precipitation and its variations. The precipitation shows a significant increasing trend (17.8 mm decade(-1)). The precipitation variability (PV) is larger at daily scale and smaller at interannual scale. The spatial distribution of PV varies on different timescales, which reflects the different dominant regimes driving the moisture transport. The mean precipitation in the TRHR is predominantly contributed by western and southern moisture influxes, and the increasing trend of these influxes (10.8 kg s(-1) decade(-1)) determines the precipitation increase. Local evaporation provide about 6% of water vapor for the precipitation, while it has little influence on the precipitation change. The anomalous precipitation in wet and dry years is mainly controlled by the atmospheric circulation over the Tibetan Plateau, which regulates the southwestern moisture transport towards the TRHR. Additionally, the precipitation during 1990-2020 increases by about 3.9% compared to that during 1960-1989. It is related to the higher conversion ratio of water vapor influxes to precipitation and larger evaporation over the TRHR. These findings improve our understanding of the precipitation variations in the TRHR and provide insights for policy makers to optimize water resources management to cope with the global climate change.