Abstract:

The impacts of climate and land use changes on runoff variation were significant. The Bahe River Basin was selected as the study area to explore the characteristics and response mechanisms of runoff variation in a typical urban watershed at the northern foot of the Qinling Mountains under the influence of both factors. Hydrometeorological data from 1960 to 2018 and land use data from 1985 to 2018 in the Bahe River Basin, methods including the sliding T-test, Trend-Free Pre-Whitening Mann-Kendall (TFPW-MK) rank test, Continuous Wavelet Transform (CWT), Cross Wavelet Transform (XWT), and Wavelet Transform Coherence (WTC), were employed to study the characteristics of hydrological, meteorological, and underlying surface element changes in the watershed, as well as the resonance periods, correlations, and temporal characteristics of watershed runoff and meteorological elements. Additionally, the Soil and Water Assessment Tool (SWAT) model was used to explore the response mechanisms of watershed runoff to climate and land-use changes under various scenarios. The results indicate that 1) from 1960 to 2018, runoff in the Bahe River Basin showed a significant decreasing trend, while urban construction land increased nearly threefold, and the area of cultivated land decreased from 1985 to 2018. 2) In the time-frequency domain, runoff and meteorological factors exhibited resonance periods and time lag effects at different scales. Precipitation and runoff showed five significant resonance periods in the high-energy area, whereas temperature and runoff presented three significant resonance periods, with runoff lagging behind changes in meteorological factors. 3) Annual runoff was positively correlated with precipitation and negatively correlated with temperature. Precipitation is the dominant factor affecting watershed runoff, and under scenarios of increased precipitation, the sensitivity of runoff to precipitation changes was higher than that under scenarios of decreased precipitation. The conversion of cultivated land to forest land may lead to a 2.58% decrease in annual runoff, whereas the conversion of grasslands to forests may increase annual runoff by 0.822%. The conversion of all cultivated land to urban construction land may increase annual runoff by 40.8%. 4) Under the combined effects of climate and land use changes, the variation range of runoff in the Bahe River basin was −0.870 m³∙s⁻¹, with climate change causing a variation range of −1.04 m³∙s⁻¹, and land use change causing a variation range of 0.170 m³∙s⁻¹. Compared with land-use change, climate change had a more significant impact on runoff variation in the Bahe River Basin.

Key words: climate change, land use change, cross wavelet transform, wavelet coherence, runoff, SWAT model, Bahe River basin

摘要：

气候和土地利用变化对径流变化的影响显著，为探究两者影响下秦岭北麓典型城市流域径流的变化特征及响应机制，选择灞河流域为研究对象，根据灞河流域1960－2018年水文气象数据和1985－2018年土地利用，采用滑动T检验、TFPW-MK秩次检验、连续小波变换（CWT）、交叉小波变换（XWT）、小波相干分析（WTC）等方法对流域水文、气象及下垫面要素的变化特征及流域径流与气象要素的共振周期、相关性与时滞性进行了研究；并结合SWAT模型，通过设置多种变化情景探明流域径流对气候和土地利用变化的响应机制。结果表明：1）1960－2018年灞河流域径流量呈显著下降趋势，1985－2018年灞河流域城镇建设用地增加了近3倍，耕地面积呈减少趋势；2）径流与气象因子在时频域中均存在不同尺度的共振周期和时滞效应，降水和径流在高能区存在5个显著的共振周期，气温和径流在高能区存在3个显著的共振周期，且径流滞后于气象因子的变化；3）年均径流量与降水量呈正相关，与气温呈负相关，流域径流变化主要由降水主导，且在降水增加情景下，径流对降水变化的敏感性高于降水减少情景；耕地全部转化为林地会导致年径流量减少2.58%，草地全部转化为林地会使年径流量增加0.822%，耕地全部转为城镇建设用地使年径流量增加40.8%；4）气候和土地利用变化共同作用下，灞河流域径流变幅为−0.870 m³∙s⁻¹，其中气候变化引起的径流量变幅为−1.04 m³∙s⁻¹，土地利用变化引起的变幅为0.170 m³∙s⁻¹，相比土地利用变化，气候变化对于灞河流域径流变化的影响更显著。

关键词: 气候变化, 土地利用变化, 交叉小波变换, 小波相干, 径流, SWAT模型, 灞河流域