Assessing the Runoff Response to Vegetation Cover and Climate Change in a Typical Forested Headwater Watershed

River source areas play a critical role in water conservation and hydrological regulation. In recent years, climate change and human activities have significantly altered the runoff in forested headwater watersheds, yet the combined impacts of these environmental changes on ecologically fragile headwater zones remain insufficiently considered. This study employed a segmented calibration approach of the Soil and Water Assessment Tool (SWAT) model in the Kuduer River Basin, located in the Greater Khingan Mountains, to evaluate runoff responses to climate change and vegetation cover variations. The results revealed that: (1) From 1985 to 2019, the basin exhibits a warm-dry trend, with a slight reduction in runoff, an increase in forest area, and a decrease in grassland area; these patterns are more pronounced during change periods. (2) Runoff is positively correlated with precipitation and negatively correlated with temperature, showing higher sensitivity to precipitation changes. Forests play a crucial role in regulating water resources, and afforestation tends to reduce runoff volumes. (3) Sub-watershed analyses reveal spatial heterogeneity: upstream areas benefit from more stable runoff due to forest cover, whereas downstream areas display greater variability. Moreover, although both climate change and vegetation cover jointly influence runoff, climate change exerts a stronger effect. Given the high sensitivity of the hydrological response in this watershed, future management measures should take into account the negative impacts of climate change and human activities on water resources.