青海湖是我国面积最大的内陆咸水湖泊，是维系青藏高原东北部生态安全的重要水体，而青海湖流域则是青海省生态旅游业、草地畜牧业等社会经济发展的重点地区。近几十年来，在气候变化和人类活动的共同影响下，青海湖水位明显下降、环湖草地退化、沙化土地扩张，整个流域正面临着极其严重的生态和环境变化危机。水是青海湖流域各生态系统之间相互联系的中心纽带，水循环过程是流域生态演变的关键驱动因子，所以从流域整体出发，准确理解流域草地、灌丛、农田和沙地等不同生态系统的生态水文过程及其生态需水规律是青海湖流域生态环境保护和恢复的关键。论文通过对青海湖流域4种典型陆地生态系统（草地、灌丛、农田和沙地）生态水文过程的野外观测，定量分析了不同生态系统的冠层截留-入渗-地表径流-土壤水分变化-蒸散发过程；在此基础上将遥感反演、统计分析、野外调查、定点观测等方法相结合，研究了流域范围内草地、灌丛、农田、沙地、河流、湖泊等6种单一生态系统类型的生态耗水/需水特征；最后结合水量平衡对整个流域及其主要生态系统类型的生态需水时空分布进行了对比。主要结论包括：（1）青海湖流域灌丛、草地、农田、沙地生态系统的降雨再分配过程和土壤水分变化具有较大差异。灌丛通过冠层能够截留34%左右的降雨，穿透雨量和树干茎流量占同期降雨量的比例分别介于60.45～61.07%、6.45～7.42%。灌丛、草地、农田和沙地生长季（5～9月）1 m深度内平均土壤水分含量分别介于25.50～34.60%、13.63～22.86%、26.77～30.24%、9.21～14.96%；灌丛和草地表层0～30 cm为土壤水分剧烈变化层（变化幅度大于14%），30 cm以下相对稳定（变化幅度小于5%）；农田0～10 cm土壤水分变化剧烈（变化幅度大于9%），10 cm以下为相对稳定层（变化幅度小于3%）；沙地不同深度土壤含水量变化幅度均小于5%。生长季农田、草地、灌丛蒸散发量分别为312 mm、295 mm、287 mm，显著高于沙地（171 mm），表明沙地蓄水作用明显。（2）以野外观测结果为基础，采用三温模型结合遥感数据，反演了青海湖流域4种典型陆地生态系统的生态耗水量（蒸散发），结果表明不同时点各生态系统蒸散发量的分布存在差异。2009年9月28日4种陆地生态系统的蒸散发量主要集中分布于1.00～3.50 mm/d，其中农田日蒸散发量最大，草地和灌丛居中，沙地最小。整个流域2009年和2010年的蒸散发量平均分别为387 mm、372 mm，占当年降雨量的比例分别为86.78%、88.17%，2010年全年尺度灌丛蒸散发量（385 mm）略高于草地（369 mm），农田蒸散发量居中（335 mm），沙地最小（320 mm）。（3）以青海湖裸鲤为指示生物计算了青海湖流域主要河流的生态需水量，布哈河、沙柳河以及整个流域全部河流P≥50%年份“中”生态需水等级下生态需水量分别介于1.94×108～2.38×108 m3、1.35×108～1.77×108 m3、5.31×108～6.71×108 m3。全年尺度河流生态需水可以得到有效满足，但关键月份仍然存在生态缺水，4～5月份河流生态需水供需矛盾突出，其中布哈河生态缺水0.29×108 m3、沙柳河生态缺水0.21×108 m3。（4）结合湖面微气象观测数据和水量平衡方程，分析了青海湖湖体的生态需水特征，结果显示2010年维持青海湖湖面蒸发的需水量为35.20×108 m3，目前青海湖湖体仍然处于生态缺水状态，要想恢复平水年（P＝50%）的湖水位需要补水5.40×108 m3，不同水平年（P＝50%、80%、90%、95%）青海湖生态需水量分别为40.66×108 m3、34.92×108 m3、34.37×108 m3、34.28×108 m3。（5）综合野外观测结果、遥感反演结果以及河流和湖泊生态需水的计算结果，研究了青海湖流域整体及其主要生态系统类型的生态需水规律，结果表明2010年青海湖流域整体生态需水量为129.52×108 m3，其中生态缺水量为4.37×108 m3，而流域生态需水的满足需要考虑年际尺度的平衡。气温上升1 K和2 K情景下，整个流域生态需水量将分别增加3.80×108 m3、7.92×108 m3，其中湖泊生态需水对气候变化的响应最为敏感。农田全部退耕后对流域生态需水的影响较小，农田灌溉可以采用冬灌方式并倡导节水灌溉模式。

Qinghai Lake, the largest saline lake in China, is an important water body to sustain the ecological security in the northeast of Tibetan Plateau, and Qinghai Lake Watershed (QLW) is a key area for the touring and husbandary industries in Qinghai Province. In the past few decades, however, the water level of Qinghai Lake declined sharpely under the influence of climate change and anthropogenic activities, which have also led to the severe grassland degradation and rapid spread of desertification. Consequently, the entire watershed is now in a critical ecological crisis. Water is suggested as a bridge to connect all the ecosystems in QLW together, and the hydrological cycle is the key driving factor affecting the ecological evolution in this watershed. Therefore, it is essensial to study ecohydrological processes and ecological water requirements (EWRs) for different ecosystems in QLW, and it is the foundation for the eco-environmental projection and recovery in this watershed.Based on the field observation of ecohydrological processes for four typical terrestrial ecosystems (grassland, shrub, cropland, sandy land) in QLW, this study analyzed their main hydrological processes, including canopy interception, infiltration, surface runoff, soil water content change and evapotranspiration (ET). Then, ecological water consumptions or EWRs for six single ecosystems (grassland, shrub, cropland, sandy land, river, lake) in QLW were studied, according to the application of remote sensing retrieval, statistical analysis, field investigation and fixed-point observation. At last, the temporal and spatial distribution characteristics of EWRs for the entire watershed and its major ecosystems were compared. The results indicated that:(1) There were obvious differences of rainfall partitioning process and soil water content change between shrub, grassland, cropland and sandy land in QLW. About 34% rainfall was intercepted by shrub canopy, while the stable percentage of throughfall and stemflow accounting to the corresponding rainfall was 60.45~61.07%, 6.45~7.42%, respectively. The average soil water content at 0~1 m layer in the growing season (May to September) was between 25.50~34.60%, 13.63~22.86%, 26.77~30.24%, 9.21~14.96% for shrub, grassland, cropland and sandy land. Soil water content changed significantly at 0~30 cm layer with a variation higher than 14% for shrub and grassland, and was relatively steady below the depth of 30 cm. While it changed significantly only at 0~10 cm layer for cropland. The change range of soil water content for sandy land at different depths was all lower than 5%. The total ET for cropland, grassland and shrub was 312 mm, 295 mm, 287 mm, respectively, which were all higher than sandy land (171 mm), indicating that sandy land was conducive to store water resources.(2) EWRs for four typical terrestrial ecosystems in QLW were retrieved from the Remote Sensing Images by applying the three temperature model, and there were obvious differences between them at different time. ET for these four terrestrial ecosystems on September 28 2009 was mainly between 1.00~3.50 mm/d, while the cropland had the maximum value, and the sandy land had the minimum value. The total ET for the entire watershed in 2009 and 2010 was 387 mm, 372 mm, accounting for 86.78% and 88.17% of the corresponding annual precipitation. On the yearly scale, ET for shrub was higher appreciably than grassland, while the ET for cropland and sandy land was medium and the lowest, respectively.(3) Annual EWRs for Buha River, Shaliu River and all rivers in QLW were 1.94×108~2.38×108 m3, 1.35×108~1.77×108 m3, 5.31×108~6.71×108 m3, respectively, in normal and dry years (P≥50%), for the recommended grade of “medium”. The contradiction between supply and demand of EWRs was significant in April and May, and the corresponding ecological water shortage was 0.29×108 m3 for Buha River and 0.21×108 m3 for Shaliu River.(4) EWRs for Qinghai Lake were 35.20×108 m3 in 2010. Currently, the Qinghai Lake was under the situation of ecological water shortage. In order to restore the water level to that in the normal year (P＝50%), the reschage of water resources was 5.40×108 m3. EWRs for Qinghai Lake at different frequency years (P＝50%, 80%, 90%, 95%) were 40.66×108 m3, 34.92×108 m3, 34.37×108 m3, 34.28×108 m3, respectively.(5) In 2010, EWRs for the entire watershed were 129.52×108 m3, in which the ecological water shortage was 4.37×108 m3, and the inter-annual balance should be considered for the satisfaction of EWRs. EWRs would increase 3.80×108 m3, 7.92 ×108 m3, if the air temperature increased 1 K or 2 K, in which EWRs for the lake were the most sensitive to climate change. The implementation of return cropland to grassland or forests had low influence on EWRs in QLW, and the more rational irrigation mode was winter irrigation and water saving irrigation.