Sensitivity analysis of runoff to climate variability and land-use changes in the Haihe Basin mountainous area of north China

Runoff has changed significantly in most regions in China over the past decades. Climate variability and land-use changes are considered to be the two main factors contributing to runoff variation. Investigating the mechanism of runoff variation is of great significance for the sustainable utilization of water resources. In this study, Mann-Kendall test, double cumulative curve method, and runoff sensitivity analysis method are adopted to separate and quantify the relative impacts of climate variability and land-use changes on runoff. Furthermore, the sensitivities of runoff were estimated with regard to these two factors in north China during the study period from 1957 to 2000. The results revealed a significant decreasing trend in annual runoff and indicated that land-use changes had a greater effect on runoff than climate variability since 1979. The runoff decline due to land-use changes was 68.33%, whereas the runoff decline due to climate variability was only 30.85%. Further analysis of the sensitivities of runoff to climate variability and land-use changes suggested that, with a 10% increase in precipitation, the runoff will increase by 35.1%; while a 10% increase in potential evapotranspiration or the aridity index will induce 25.1% or 27.5% decrease in runoff, respectively. The sensitivity coefficients of runoff to precipitation, potential evapotranspiration and aridity index (εP, εEP and εϕ), and runoff ratio (Q/P) and the aridity index exhibited a significant nonlinear negative correlation (Y = ax−b, R2 > 0.85), and a positive linear correlation (Y = ax + b, R2 < 0.50), respectively. All these results implied that runoff is more sensitive to the regions with water scarcity and drying climate. The average sensitivity coefficients of runoff to forest, grassland, and farmland were 1.46, 1.21 and 1.18, respectively. This means that a 10% increase in forest, grassland, and farmland coverage would induce 1.46, 1.21, and 1.18 mm decrease of runoff, respectively. This demonstrates that forests have the most effective impact on runoff reduction, followed by grassland or farmland.