Land Use/Cover Change Reshapes Water Balance Components Across Spatial Scales in a Typical Humid Hilly Region

Land use/cover change (LUCC) can alter watershed water balance, while whole-watershed averages may obscure spatial heterogeneity among sub-basins. This study evaluated LUCC-induced hydrological responses in the northern region of Longyou County, Zhejiang Province, China, a subtropical humid hilly area. Land use maps for 2008, 2013, 2018, and 2023 were used to construct four SWAT scenarios under identical meteorological forcing, and partial least squares regression (PLSR) was applied to examine associations between land-cover changes and modeled hydrological responses. The classified maps indicated decreases in cropland and barren land and increases in forest and settlement between 2008 and 2023. Scenario simulations showed lower water yield and higher evapotranspiration under LU2023 than LU2008; these responses were robust, whereas surface runoff, lateral flow, and groundwater contribution were more model-sensitive. At the sub-basin scale, greater forest expansion was associated with larger decreases in surface runoff and water yield and greater increases in evapotranspiration. PLSR further identified forest as the most influential land use predictor for these three responses, although model explanatory power was moderate. These results highlight spatial heterogeneity in modeled LUCC responses and the value of sub-basin analysis for water management.