2000—2018年黄河上中游地区蒸散发年际时空变化及其影响因素分析

黄河流域水资源匮乏且生态系统脆弱，明晰气候与下垫面变化对蒸散发（ET）时空变化的影响机制对于未来黄河流域水资源优化配置与生态建设规划均具有重要意义。基于实测降雨、径流量和GRACE产品数据，利用线性加权融合方法对5种全球ET产品进行融合。利用去趋势法、多元线性回归、全微分和残差法定量计算ET对降雨（Pre）、温度（Temp）、日照时数（SD）、饱和水汽压差（VPD）、风速（WS）和植被叶面积指数（LAI）的敏感性系数，定量分析了各气象要素、植被和其他要素（微地形变化和农业灌溉等）对ET变化趋势的贡献作用。结果表明：①与验证精度最高的GLDAS_CLSM相比，融合ET均方根误差和平均相对误差分别减小12.8 mm和2.2%。2000—2018年黄河上中游ET净增长率为3.82 mm/a，头道拐—龙门区间ET增长率最大（6 mm/a）。②植被LAI显著增加导致上中游区ET趋势增加2.49 mm/a。各气象要素的变化趋势与ET对其敏感性系数的空间异质性共同决定了气象要素对ET的影响作用空间分布，5个气象要素对ET总体趋势的净影响量均为正值，其中温度影响作用最大（0.33 mm/a）。以微地形变化和灌溉活动为主的其他要素导致ET趋势增加0.5 mm/a，相对影响率为13.1%。③气象要素主导源区和唐乃亥—青铜峡区间ET趋势，而植被LAI主导了青铜峡-花园口区间ET趋势，其中LAI对不同子流域ET趋势影响作用排序为：延河>无定河>泾河>北洛河>汾河>窟野河>伊洛河>沁河>渭河>大黑河。其他要素对唐乃亥—青铜峡和龙门—花园口区间的ET影响作用较大，表明该区域的水利水保工程措施和灌溉等人类活动更为剧烈。

Analysis of Spatio-temporal Dynamics of Interannual Evapotranspiration and Its Influencing Factors in the Upper and Middle Reaches of the Yellow River from 2000 to 2018

Yellow River Basin （YRB） has been facing issue of severe water shortage， hence detection and attribution of spatio-temporal variation of Evapotranspiration （ET） in the YRB is very significant for optimal allocation of water resources and sustainable development of social-economy and eco-environment. Combined with measured rainfall and runoff and GRACE product， five global ET products were merged by an linear weighting method. Detrended scheme， multiple linear regression， partial differential and residual method were then employed to calculate the sensitivities of ET to Precipitation （Pre）， Temperature （Temp）， Vapor Pressure Deficit （VPD）， Sunshine Duration （SD）， Wind Speed（WS） and Leaf Area Index （LAI）， and quantitative impacts of different climatic factors， LAI and residual factors （microtopography change， irrigation， impoundment of reservoir， etc.） on the ET trend. ① Compared to the GLDAS_CLSM with best performance， RMSE and MRE of the merged ET were reduced by 12.8 mm and 2.2% respectively. The growth rate of ET over the whole study area during 2000—2018 was 3.82 mm/a， and the ET trend of Toudaoguai-Longmen was highest （6 mm/a） among all subregions. ② Dramatic increasing of LAI improved the ET trend by 2.47 mm/a in the upper and middle reaches of the Yellow River Basin. Spatial heterogeneity of change trend of meteorological factors and sensitivities of ET to them determined the spatial pattern of impacts of meteorological factors on the ET trend. The net impact of all five meteorological factors on the trend of ET was positive， with Temp having the largest impact （0.33 mm/a）. The impact of residual factors on ET trend mainly induced by microtopography change and irrigation should also not be neglected， with impact and relative impact rate of 0.5 mm/a and 13.1%. ③the ET trends of source area and Tangnaihai-Qingtongxia were dominated by climatic factors. Vegetation restoration is the dominant factor for ET increasing trend in the middle reaches， where the impact rates of LAI on the ET trend were ranked as follows： Yanhe Rive > Wudinghe River > Jinghe River > Beiluohe River > Fenhe River > Kuyehe River > Yiluohe River > Qinhe River > Weihe River > Daheihe River. Residual factors have higher effects on ET in the Tangnaihai-Qingtongxia and Longmen-Huayuankou subregions， indicating that human activities such as water conservation engineering measures and irrigation are more intense in this region.