Runoff contribution of spring snowmelt in the source region of the Yangtze River and its variation characteristics

Study region: The source region of the Yangtze River (SRYR), located in the remote Tibetan Plateau, features high elevations and significant seasonal snow cover. Study focus: This study examines spring snowmelt contributions to runoff in the SRYR during 1980-2022 using the Variable Infiltration Capacity (VIC) model, the Third Pole Meteorological Forced Data (TPMFD) dataset, and streamflow data from the Zhimenda station. It focuses on the spatiotemporal dynamics of snowmelt, climate warming impacts, snowmelt-induced flood risks, and precipitation phase changes (rain vs. snow). Key factors addressed were: 1) how snowmelt contributions vary spatially, temporally, and with elevation; and 2) how shifting climate and precipitation affect snowmelt and related hydrological risks. New hydrological insights for the region: The spring snowmelt period in the SRYR has shortened (-3.3 days/10a), while snowmelt-induced flood risks have risen. Snowmelt contributions have increased at high elevations (4400-5200 m), with snowmelt occurring earlier and contributing more in April (1.03 %/10a) and May (1.62 %/10a), but less in June (-1.1 %/10a). Extreme snowmelt runoff events have surged from 3 to 7 per year, with flood risk exceeding 57 %. Precipitation phase changes, especially liquid precipitation, amplify snowmelt and runoff fluctuations. These compounded risks highlight the accelerating impacts of climate warming on the SRYR hydrological system, emphasizing the need for improved flood management and climate adaptation.