涪江流域径流对气候与土地利用的响应

Responses of streamflow to climate and land use changes in Fu River Watershed

为探究长江上游涪江流域地表径流对气候变化和土地利用变化的响应,采用Mann-Kendall趋势检验法和Sen斜率分析法综合分析1980—2015年间水文气象序列变化趋势;双累积曲线法和Pettitt突变检验法确定突变年份;利用土地利用转移矩阵分析流域土地利用变化;基于SWAT模型,构建气候和土地利用变化在单独和共同作用下的径流响应情景。结果表明:1)研究期间,年径流量呈显著下降趋势,年降雨量也呈下降趋势,但不显著;以2000年为突变年,年径流量呈现“先下降后上升”的阶段性趋势。2)流域最主要的土地利用类型为耕地(58.80%),研究期间面积减少最多;变幅最大的为未利用地和城镇用地。3)采用决定系数R^(2)、纳什效率系数E_(ns)和百分比偏差PBIAS对SWAT模型进行评价,结果表明SWAT模型在该流域具有很强的适用性。4)与基准期相比,全流域角度:仅降雨变化或仅土地利用变化,可分别使产流量减少10.47%和1%,当二者同时发生变化,产流减少16.01%;子流域角度:上游未利用土地增加,加大水土流失风险;下游城镇扩张增加作用显著产水量;河道2侧退耕还林(草)措施调蓄径流作用显著。气候和土地利用变化对径流的贡献呈非线性关系,且气候变化对流域的产流变化起主导作用。研究结果可为流域水资源管理、开展水土流失治理及三峡的入库径流测算提供依据。

[Background]Climate change(CC)and land use and land cover change(LUCC)are two driving factors affecting streamflow within a watershed.The Fu River Watershed(FRW)was selected as the study area due to its critical location to the upper Yangtze River.This study aims to quantify streamflow reduction under the sole and combined effects of CC and LUCC at multiple spatial scales.[Methods]Two combined used techniques,Mann-Kendall test and Sen′s slope estimator,were selected for trend analyses.Double Mass Curve(DMC)and Pettitt test were used for the abrupt point detection.Transition matrix was adopted to analyze the variation of land use type before and after the detected abrupt year.Two time periods were divided by the abrupt year and four different scenarios were set up to simulate the sole and combined effects of CC and LUCC.Streamflow discharges for different scenarios were driven by SWAT simulation.[Results]1)During the entire period,annual streamflow showed a significant reduction trend with a confidence level of P<0.01 and annual precipitation exhibited a downward trend,respectively.The year 2000 was detected as the abrupt point,and the whole time series presented characteristics of“decreasing at the first stage and increasing at the second stage”.2)The primary land use type of the FRW was farmland(58.80%),which decreased by 427.98 km^(2) during the study period.The areas of unutilized and urban land were relatively small,yet with largest growth rates(218.80%and 195.58%,respectively).3)The R^(2),E_(ns),and PBIAS were selected as model evaluation indices,the values for which were 0.89,0.88,and-0.2%for calibration period,respectively,and 0.82,0.82,and 6.8%for validation period,respectively.This demonstrated that the SWAT could be satisfactorily used in FRW.4)Four scenarios were constructed during the basic period(1980-2000)and the varied period(2001-2015),and results showed that:at the whole basin scale,water yield(WYLD)under scenario 1(with isolated variation of precipitation),scenario 2(with isolated variation of land use)reduced by 10.47%and 1%,respectively.However,WYLD under scenario 3(with combined variations of precipitation and land use)reduced by 16.01%.At the sub-basin scale,the increase of unutilized in the upstream increased the risk of soil erosion.On the other hand,the expansion of urban land at downstream increased the WYLD,while the effects of Grain-to-Green project on both bank regions of the river channel significantly reduced streamflow discharge.[Conclusions]Both CC and LUCC will affect WYLD of FRW at basin scale and sub-basin scale.It is remarkable that the combined effects of CC and LUCC are not equal to sum of corresponding sole effect,which is potentially due to the interactions between the climate and land use types.This research may provide reference for water resource management,soil and water conservation and reservoir streamflow forecast of the Three Gorges Dam.