变化环境下的流域生态水文过程演变研究对国家水安全、生态安全和粮食安全等重大需求具有十分重要的理论意义和实践价值。开展气候和下垫面变化综合影响下的生态水文过程时空演变格局分析，有利于深入了解水循环与水资源演变机制，为流域水安全和生态安全保障提供技术支撑。本文选择黄河兰州水文站以上区域作为研究区，基于地形地貌、生态因子、气象要素、水文指标和人类活动共5个方面筛选分区指标，构建黄河源区生态水文综合指标体系，采用主成分分析和聚类分析方法，结合水文站点位置、子流域分布和气候系统等信息，划分生态水文分区；通过土地利用转移矩阵分析下垫面动态演变格局，Sen’s slope和Mann-Kendall趋势分析法识别1980-2019年黄河源区不同生态水文分区气候、生态和水文关键要素的时空演变规律，双累积曲线法和相关性分析法探究各要素间的相互作用关系；基于水文、植被、土壤和气象等多源数据，构建VIC陆面过程模型对黄河源区近四十年的径流和蒸散发过程进行模拟研究。研究主要结论如下：

（1）综合生态水文指标体系分析结果、水文站点位置、子流域分布和行政区划等信息，将黄河源区划分为3个一级和7个二级生态水文分区。其中，I区西南部低植被覆盖少水区，区内高程在4000 m以上，几乎无人类活动影响，根据水文过程划分为以冻土水文过程为主的I-1区和以融雪过程为主的I-2区；II区中部高植被覆盖丰水区和III区东北部中等植被覆盖平水区以降雨径流过程为主，II区土地覆被简单，主要受自然条件影响，根据气候系统划分为主要受季风气候影响的II-1区和受西风环流影响的II-2区；III区受人类活动影响大，耕地集中分布在该区，根据气候带划分为III-1区、III-2区和III-3区。

（2）黄河源区1980-2019年气温和叶面积指数持续增加，空间上气温自西南向东北递增，叶面积指数西低东高，III-2区水热条件好，植被叶面积呈显著增加趋势。降水、积雪深度和径流在1980-1999年以减少趋势为主，2000年以后逐渐增加，降水自西北向东南递增，年内集中分布在6-9月，积雪主要分布在I-2区昆仑山脉和III-3区祁连山区附近。黄河源区叶面积指数与气温和降水呈显著正相关关系，不同分区间的交界处高程起伏大，植被对气温的响应存在1个月的滞后效应，I区和II-2区植被与降水的相关系数在滞后1个月时达最大值。

（3）VIC模型在黄河源区月径流模拟中表现出较好的效果，细化不同生态水文分区的参数方案有利于优化模拟结果，其中，唐乃亥站在率定期和验证期的纳什效率系数NSE和确定性系数R²均在0.8左右。黄河源区蒸散发量自西北向东南递增，I-1区和III-3区降水稀少，草地的蒸散发量较小，2000年以后研究区蒸散发量明显增加。黄河源区降水主要通过蒸散发过程损失，大部分地区径流系数在0.2以下。黄河源区融雪径流与积雪的空间分布基本一致，I-2区和III-3区积雪深度较厚的区域融雪径流在总径流中的占比在20%以上，II-1区和III-1区季风气候影响较大的区域以降雨径流为主的其他径流占比在90%左右。

The study on the evolution of ecohydrological process under changing environment has very important theoretical significance and practical value for the securities of water resources, ecological environment and food. The spatiotemporal evolution patterns on the ecohydrological process under the influences of climate and underlying surface changes are conducive to the in-depth understanding about the changing mechanism of hydrological cycle, and also can provide guidance for the water and ecology protection. In this paper, the region above Lanzhou hydrological station of the Yellow River was selected as the study area, and the ecohydrological index system was constructed from five different aspects, including the terrain and geomorphology, ecological factors, meteorological elements, hydrological indexes and human activities. The ecohydrological zones in the study area were divided based on the results of principal component analysis and cluster analysis about the indexes, the distributions of hydrological stations, sub-basins, and climatic zones. The land use transfer matrix was used to analyze the dynamic evolution pattern of underlying surface. The spatiotemporal changing trends and interaction of ecological and hydrological processes in the study area during the period 1980-2019 were investigated by the Sen's slope and Mann-Kendall trend analysis, accumulation curve and correlation analysis methods. Based on the multi-source datasets of hydrology, vegetation, soil and meteorology, the land surface process model (VIC) was used to simulate the ecohydrological process for the past forty years. The main conclusions are as follows:

(1) Considering the ecohydrological indexes, the distributions of hydrological stations, sub-basins and administrative divisions, the study area was divided into three first-level and seven second-level ecohydrological zones, among which the zone I was in the southwest, with the low vegetation coverage and little water, where had the average elevation more than 4000 m and almost unaffected by human activities. Zone I was divided into two regions depending on the main hydrological process of frozen soil (I-1) or snowmelt (I-2). Zone II and III were dominated by the rainfall and runoff process, where the zone II was mainly influenced by the natural conditions and had the higher vegetation coverage and precipitation than zone III. According to the climate system, zone II was divided into II-1 which was mainly affected by monsoon climate and II-2 which was mainly affected by westerly wind circulation. The cultivated land was concentrated in the zone III, which was divided into III-1, III-2 and III-3 according to the climatic zones.

(2) In the source region of the Yellow River, the temperature was increased from southwest to northeast, the leaf area index was low in the west and high in the east with a significant improvement in zone III-2, both them had a continuous upward trend during the period 1980-2019. Precipitation, snow cover depth and runoff decreased during the period 1980-1999, and then gradually increased after 2000. Precipitation increased from northwest to southeast, and the snow cover mainly distributed in the Kunlun Mountains in zone I-2 and Qilian Mountains in zone III-3. There was a significantly positive correlation among leaf area index, temperature and precipitation in the study area. The response of vegetation on the temperature had one-month lag in the junctions of different zones, and the correlation coefficient between vegetation and precipitation in zone I and II-2 reached the maximum value with a lag of one month.

(3) VIC model showed relatively accurate results in the simulation of monthly runoff, and refining the parameters at different ecohydrological zones could optimize the simulation results in the source region of the Yellow River. The Nash efficiency coefficient (NSE) and deterministic coefficient (R²) of the Tangnaihai station in the calibration and validation periods were about 0.8. The evapotranspiration of the study area had obviously raised trend after 2000 and spatially increased from northwest to southeast. Zone I-1 and III-3 had the low precipitation and evapotranspiration, where mainly covered by the sparse grassland. Most of the precipitation lost through the evapotranspiration process, and the runoff coefficient was generally below 0.2 in the source region of the Yellow River. The spatial distributions of snowmelt runoff and snow cover in the study area were basically the same. Snowmelt runoff in zone I-2 and III-3 with thicker snow depth accounted for more than 20% of the total runoff, while mainly rainfall runoff in zone II-1 and III-1 with greater monsoon climate influences accounted for about 90%.