西北内陆河流域水循环和生态演变与功能保障机制研究

A comprehensive study of the maintaining mechanisms for hydrological cycle and ecological evolution and function in the northwest inland river basins of China

在气候变化、生态保护以及水资源调控影响下,西北内陆河流域水循环和生态环境状态发生了显著改变,迫切需要解答气候变化对植被恢复和产水量的影响,调水和压采等措施下地下水水位动态、管控指标及其对生态环境的维持机制。为此,文章阐述了内陆河流域气候-植被-土壤-水文相互作用机理以及上中下游演变状况。针对上游产水区,提出了山区气候变化下植被和水文动态演变模拟和预测方法,得出石羊河上游山区气候暖湿趋势和植被水分利用效率的提高,可降低植被恢复对增加蒸腾量、减少产水量的影响程度;但如未来继续升温,水分利用效率提高的正效应将被植被恢复增加的水分消耗抵消,从而减小径流量。针对中下游绿洲-荒漠过渡区,通过分析荒漠植被-土壤(水盐)-地下水作用机理,提出了西北干旱区生态地下水水位埋深和生态需水量确定方法及阈值,得出荒漠植被适宜和极限生态地下水水位埋深的平均值分别为2.9 m和5.5 m,对应埋深下的单位面积荒漠植被生长季平均蒸腾耗水量为0.08~0.10 m^(3)/m2。针对尾闾湖区,建立生态输水量与尾闾湖地下水水位、生态指标之间关系,提出了石羊河流域尾闾湖生态输水优化方案,得出青土湖生态输水量应提高至0.45×10^(8) m^(3)/a。在流域层面,采用水资源-社会经济-生态环境协调的系统分析手段,提出了石羊河流域满足地下水均衡、供需平衡和生态功能的多水源调控方案,即“保田增林”或“以田换林”方案。

In recent decades,the hydrological cycle,ecology and environment of the inland river basins in northwest China have been significantly changed due to climate change and implementations of the ecological protection and water division projects.It is necessary to investigate how climate change affects vegetation restoration and runoff generation,and how groundwater table variation and its controlling index maintain ecology and environment under the inter-basin water diversion and reduction of groundwater withdrawal.In this study,we illustrate the mechanism of climate-vegetation-soil-hydrology interactions and their evolutions in the upper,middle and lower reaches of the catchments.For the upper reaches,we propose a method of simulation and prediction of mountain vegetation and hydrological changes under climate warming and wetting.When the method is applied in the Shiyang River basin,the results demonstrate that increase of efficient water use can reduce vegetation recover induced evaporation(thus runoff reduction).In the oasis-desert transition areas of the middle and lower reaches,we analyze desert vegetation-soil(moisture and salt)-groundwater interactions,and propose methods to determine critical values of the ecological groundwater depth and water requirement.For the terminal lake,we establish the relationships among ecological water division,groundwater table and ecological index.These relationships are used to optimize the schemes of ecological water division.In the whole inter-basin,we apply a system analysis approach of water resources-economic and social development-ecological and environment processes to obtain the schemes of the multi-water source allocations in the Shiyang River basin.These schemes can maintain groundwater withdrawal and recharge balance,water requirement and supply balance and ecological functions.