Seasonality changes in the terrestrial water cycle under different vegetation types and their attribution in the Songliao River Basin, Northeast China

Study Region The Songliao River Basin (SRB), located in Northeast China Study Focus This study focuses on the seasonality changes of the terrestrial water cycle (TWC) in the SRB from 1981 to 2020, including precipitation, snow water equivalent (SWE), runoff, evapotranspiration (ET), and soil moisture. An information-entropy-based index was used to quantify the seasonality of TWC. We employed the Mann-Kendall trend test to analyze the seasonality changes, and the SHapley Additive exPlanations to attribute these changes to the climate and vegetation factors. New Hydrological Insights A declining trend was found in precipitation seasonality in the SRB, particularly near the main streams of the Songhua, Hailar, and Xilamulun Rivers. Influenced by the rising air temperature, the seasonality of SWE experienced a significant increase in grasslands. Enhanced spring snowmelt shifted runoff to bimodal peaks in humid regions, reducing seasonality. ET seasonality significantly decreased across the SRB, particularly in the Hailar, Songhua, and eastern Liao River Basin, driven by the rising air temperature and the extended growing season. Besides, the seasonality of soil evaporation, canopy evaporation, and vegetation transpiration all decreased across all land-cover types. Soil moisture seasonality exhibited weaker trends, increasing only in the Hailaer and Xilamulun River Basins, Songnen and Sanjiang Plains. This study deepens our understanding of water cycle dynamics and provides scientific guidance for water resource management and disaster warning in the SRB.