澜沧江梯级高坝大库对跨境径流的影响及其调控阈值

The Lancang-Mekong river is the biggest international river in Southeast Asia. Under the superposed effects of climate change and hydropower development, the transboundary water security issues have become increasingly prominent.In recent years, the operation of multi-year regulating reservoirs make the flow regime transiting from a natural state to reservoir scheduling, the transboundary hydrological impacts driving by cascade development has been the focus of international concern. Therefore, to assess the transboundary hydrological impacts and identify the thresholds of flow regulation is of great significance for transboundary water security regulation. Based on the longterm observed hydrological data, this project tries to reveal the responses of tranboundary runoff to the cascade hydropower development on the Lancang River. Secondly,the influence of cascade hydropower development on transboundary flow are quantitatively assessed by using distributed hydrological model. Finally, the thresholds of flow regulation are identified based on the evaluation of instream ecological flow and analysis of transboundary water resources utilization. The project will provide a scientific basis for multi-object ecological regulation of the cascade hydropower on the Lancang river, and decision support to reduce or avoid transboundary impacts caused by cascade hydropower development and to maintain ecological security in the basin.

澜沧江—湄公河是东南亚最大的国际河流，受气候变化和梯级水电开发的影响，跨境水安全问题日益突出。近年来澜沧江具有多年调节的高坝大库运行使下游河段水文情势发生明显变化，梯级开发驱动下跨境水文效应已成为国际关注和争论的焦点。科学认识梯级开发对跨境径流的影响以及合理界定径流调控阈值，对跨境水安全调控具有重要意义。本项目基于境内外长序列水文观测数据，采用野外水文监测、RS/GIS技术和水文过程模拟相结合的方法，阐明澜沧江梯级水电开发驱动下跨境径流的响应特征；构建流域水文模型对水文过程进行模拟，定量分析梯级水电开发对跨境径流的影响；基于生态径流量识别和跨境水资源利用需求，提出面向水资源合理利用与水生态保护的径流调控阈值。研究成果将为澜沧江梯级电站多目标生态调度、规避和减少水电开发的跨境影响以及维护流域生态安全等提供科学依据。

澜沧江—湄公河是东南亚最大的国际河流，受气候变化和梯级水电开发的影响，跨境水安全问题日益突出。澜沧江高坝大库运行驱动下跨境水文效应近年来已成为国际关注的焦点，急需厘清梯级水电开发对跨境径流的影响并合理界定径流调控阈值。本项目基于境内外长序列水文观测数据，定量分析梯级水电开发对跨境径流的影响并提出径流调控阈值。主要研究成果：（1）近60年来澜沧江出境径流表现出显著的减少趋势，下湄公河干流径流变化趋势不显著；下湄公河干流站点干湿季、上下游径流变化趋势差异明显，特别是流量逆转次数以及与低流量相关的水文指标改变度较高。（2）澜沧江梯级水电开发影响期多年平均出境径流量较天然期减少8.28%，人类活动贡献了77-80%，是径流减少的主要因素；澜沧江中下游六个梯级水库的“蓄洪补枯”作用导致旱季出境径流平均增加103%，雨季径流减少35%。（3）基于遥感数据发现洞里萨湖2008-2014年平均面积相比2000-2007年间减少了6.19%，通过上下游水文关联研究表明澜沧江梯级水电开发并非洞里萨湖面积减小的最主要原因。（4）采用FDC-shifting方法估算不同河流环境管理等级下的环境流量过程较好地保持了天然水文情势。澜沧江维持环境管理等级A的环境流量（占多年平均流量79%）可以有效保护河流生态系统，而环境管理等级C（占多年平均流量48%）为维持河流基本生态功能的最低环境流量。上述研究成果可为澜沧江梯级电站多目标生态调度、规避和减少水电开发的跨境影响以及维护流域生态安全等提供科学依据。