Rising temperatures trigger warming-wetting conditions in the East River Basin, China

The East River Basin (ERB) is located at the junction of the Western Pacific Ocean, the South China Sea, and Eurasia. In 2011–2012, the ERB suffered severe droughts in all four seasons, so the wetting and/or drying tendency of the ERB had aroused widespread concern. Based on the ERA5 reanalysis and CMIP6 multi-model datasets, we used a Lagrangian trajectory model to unravel precipitation, temperature, and evaporation changes during the historical period 1981–2023 and predict wetting and/or drying tendencies (measured by precipitation minus evaporation, PME) during the future period 2024–2099. During the historical period, average annual precipitation decreased (-10.3 mm/a), evapotranspiration increased slightly (0.87 mm/a), and air temperature increased significantly (0.29°C/10a). We found that precipitation decreased over the northern and central ERB and evapotranspiration increased over the west to 115°E, while temperature increased over the eastern ERB, resulting in a warmer and drier state over the entire ERB. External water vapor input is the prime driver of precipitation change (accounting for 79 % of the total), mainly from the North Pacific Ocean (31 %) and the Indian Ocean (26 %). The net water vapor fluxes declined in the late 20th century and peaked in 2006, and then decreased rapidly until 2023, wherein internal water cycle contributed to 21 % of precipitation change. Under the 1.5°C warming scenario, ERB will be in a warming-drying state, while under higher warming levels (2°C, 3°C, 4°C warming scenarios), ERB will be in a warming-wetting tendency. These findings can provide an important reference for basin-scale water resources management and mitigation of water issues in the context of climate warming. • The East River Basin experienced significant warming and drying trends during 1981–2023. • External water vapor contributed 79 % of precipitation changes in the East River Basin. • Net water vapor fluxes peaked in the early 21st century and then gradually declined. • Warming scenarios predict a shift from drying to wetting at ≥ 2°C warming levels.