Runoff Response of the Qinhe River Basin under Climate Change and Land Use Conditions

The Qinhe River Basin is a crucial ecological barrier and water conservation area in the Yellow River Basin, playing an indispensable role in supporting national ecological protection strategies and promoting regional high-quality development. An in-depth study of its hydrological processes holds significant scientific importance and can provide key insights for sustainable management. This research investigates the coupled impact mechanisms of climate change and land use/cover change (LUCC) on runoff processes. Using meteorological data from 1979 to 2018, combined with land use data from 1990 to 2020, a multi-scenario simulation method was employed to quantitatively evaluate the contributions of precipitation, temperature changes, and LUCC to runoff. The results indicate that: (1) The SWAT model has high applicability in the Qinhe River Basin, with Nash-Sutcliffe Efficiency (NSE) and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{R}^{\mathbf{2}}$</tex> values both greater than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{0. 7 5}$</tex> during the calibration and validation periods, and the percentage bias (PBIAS) less than 10%, indicating excellent simulation accuracy; (2) Precipitation is the dominant driver of runoff change, with a 10 % increase or decrease in precipitation leading to a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$17.5 \%-25.4 \%$</tex> change in runoff. Based on the baseline scenario under constant precipitation conditions, a 1° C temperature increase reduces runoff by 3 %, while a 1° C temperature decrease increases runoff by 3.4 %; (3) From 1990 to 2020, LUCC in the study area mainly manifested as the conversion of cultivated land to builtup land (a 106.1 % expansion), which increased the impervious surface, resulting in an average monthly runoff increase of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{0. 6 6} \mathbf{m}^{3} \boldsymbol{/} \mathbf{s}$</tex> in 2010 compared to 2000, and exacerbated the risk of extreme runoff events. Based on a comprehensive analysis, climate change is the primary factor influencing runoff variation in the Qinhe River Basin, while the impact of Land Use and Cover Change (LUCC) is relatively minor, though it exhibits cumulative effects.