基于气候变化和人类用水影响下蒸散发及地下水重建的黄河流域水循环关键过程变化

The water cycle of the Yellow River basin has been changing extensively under the impacts of climate change and human activity. However, studies on the variation and mechanism of regional water cycle have been greatly limited by the lack of observations. For instance, regional evapotranspiration (ET) is always difficult to obtain. For the Yellow River basin, the extensive human interventions have altered the spatial distribution of surface water body, which makes the accurate estimation of ET more difficult. To overcome this, this study is proposed based on land-surface models, human water use, hydrometeorology measurements, and remote sensing data. First, the ET will be reconstructed using the simulated ET from land-surface models, the irrigation water, observed precipitation, and the naturalized streamflow to reduce the ET uncertainty by using multi-source datasets. The reconstructed ET will be evaluated using the water-balance equation with the terrestrial water storage change (TWSC), which is derived from the Gravity Recovery and Climate Experiment (GRACE), being taken into account. Second, the groundwater change will be estimated from the water-balance equation using the reconstructed ET and measured soil moisture. The estimated groundwater change will be compared with the result isolated from GRACE-TWSC. Finally, the variations of crucial water cycle processes and relationships among them will be discussed based on the obtained ET and groundwater. The implement of this study can provide guidance for the water cycle study and water resource management for the Yellow River basin.

受气候变化和人类活动共同影响，黄河流域的水循环正在发生显著变化。但观测数据的缺乏阻碍了区域水循环变化过程和机制的研究，如区域蒸散发数据的获取一直是公认的难题，流域内剧烈的人类活动改变了地表水体的分布状况，使蒸散发的准确估计更加困难。为此，本项目拟利用陆面模式、人类用水、水文气候观测及遥感数据为基础，首先基于陆面模式模拟的蒸散发、灌溉用水、观测降水及天然径流，重建黄河流域气候变化和灌溉影响下的实际蒸散发，采用考虑GRACE陆地水储量的水量平衡方程检验重建结果的数据质量，通过多源数据的综合利用减小重建结果的不确定性；其次，利用重建的蒸散发和观测土壤水，基于水量平衡原理，估算黄河流域的地下水变化，并与利用GRACE陆地水储量推求的地下水结果进行对比分析；最后，基于获得的蒸散发和地下水数据，分析黄河流域水循环关键过程的变化特征及相互联系。本项目的实施对黄河流域的水循环研究及水资源管理具有重要意义。

受气候变化和人类活动共同影响，黄河流域的水循环正在发生显著变化。人类用水的~70%用于农业灌溉，这使得影响地表蒸散发的过程更加复杂，无论是模式模拟还是遥感获得的蒸散发都还不能准确反应灌溉的影响。在缺乏对地表蒸散发准确估算的情况下，很难客观描述水循环变化的真实图像。为此，本项目建立考虑作物生长季的灌溉方案，对观测年灌溉耗水量时间降尺度，结合观测降水和还原的天然径流对模式蒸散发进行校正和改进，最终建立了考虑灌溉耗水的流域蒸散发的计算方案，并估算了黄河流域的地下水变化，进而分析黄河流域水循环关键过程的协同变化机制。结果表明以全球陆面数据同化系统GLDAS 1.0、2.0及2.1中四个陆面模式（Noah、CLM、VIC和Mosaic）模拟的六套蒸散发产品为初值，重建后的黄河流域蒸散发均有所改善，相关系数、纳什效率系数、平均绝对误差以及均方根误差改善0.6%–21.0%。基于GRACE重力卫星的陆地水储量估算的地下水变化，全国范围内~71%格点的变化趋势与观测结果具有相同符号，且不存在系统性偏差。地下水对陆地水储量长期变化趋势有主导作用，这与检测到两者明显的长期记忆性密切相关，正是该长期记忆性的存在导致无法使用同期降水量解释地下水和陆地水储量变化。黄河源区陆地水储量的增加对应增加的土壤水和径流，黄土高原及下游陆地水储量的减少对应减少的地下水、土壤水和径流；土壤水和地下水可以通过蒸散发影响陆地水储量，而蒸散发在流域大部分地区呈增加趋势并与叶面积指数具有较好的正相关。该项目研究成果对黄河流域的水循环研究及水资源管理具有重要意义。