Nonlinear responses of large river runoff to precipitation in eastern China under varying hydrothermal environments

Study region The seven large river basins are situated in the eastern China region (ECR). Study focus Large river basins in the ECR represent critical components of the global hydrological cycle. However, the runoff responses to precipitation under global warming and human coercion show significant heterogeneity. To address this challenge, we have developed a novel hydrological index (RP) and integrated methods including nonlinear threshold analysis and structural equation modeling to quantitatively identify the nonlinear thresholds and driving mechanisms of runoff responses to precipitation in large river basins under varying hydrothermal environment. New hydrological insights for the region Using long-term observational data, we identify distinct spatiotemporal trends in runoff and precipitation, with notable declines observed particularly across northern basins. Moreover, the declining trend in runoff and precipitation was less pronounced in northern basins than in the south. Through nonlinear threshold analysis, we reveal precipitation thresholds that mark shifts in runoff response patterns: 398.66 mm in the north and 1226.8 mm in the south. Crucially, attribution analysis indicates that runoff in northern basins is jointly affected by positive precipitation effects and negative temperature effects (β: +0.367 and −0.406, p < 0.05), whereas southern runoff is predominantly controlled by precipitation (β: 0.715, p < 0.001). This is primarily due to the arid climate leads to a stronger dependence of terrestrial water replenishment on precipitation, while high water demand from soils and vegetation exacerbates the uneven allocation of rainfall. With the increasing frequency of extreme high-temperature events driven by climate warming, the inhibitory effect of temperature on runoff will be further intensified, especially in northern basins. These results provide a mechanistic perspective on runoff–precipitation interactions and highlight a growing divergence in water availability between northern and southern China, with critical implications for future water resource planning and hydrological process research.