西风和印度季风影响下的青藏高原内流区湖泊水位变化过程及驱动机制研究

Endogenic lakes on the Tibetan Plateau (TP) interior expanded significantly since the late 1990s, which has significant impact on the regional environment and ecological system. The westerlies and Indian monsoon are two key climate systems on the TP. In winter, the plateau is mainly dominated by the westerlies, and in summer the south of the plateau is mainly influenced by Indian summer monsoon and the north is still mainly controlled by the westerlies. Although there are a lot of studies about lake dynamics on the TP, the process of inter-annual lake level change and the response to changes in the westerlies and monsoon are still unclear. Based on extensive field observation in combination with regional precipitation, simulated lake evaporation and runoff into the lake, this project aims to carry out the monitoring of inter-annual lake level changes in the westerlies and monsoon dominated regions, as well as the margin of Indian summer monsoon region, analyze the spatial and temporal characteristics of this process in different climate regions, discuss its relationship with regional precipitation, lake evaporation and runoff, and reveal the difference of how these factors influence the lake level changes. On longer time scale, this project aims to analyze the difference of lake dynamics since the 1970s in the westerlies and monsoon dominated regions, reveal the response of lake dynamics to changes in large scale atmospheric circulation, and discuss the mechanism of lake expansion in recent decades. This study are not only of great importance to understand the changes in hydrological cycle in the third pole region under global warming, but also useful to understand the mechanism for the high lake level on geological time scale.

青藏高原内流区湖泊近十多年来普遍出现快速扩张，对区域生态环境产生了重要影响。西风和印度季风是影响青藏高原气候环境变化的两大主要气候系统，尽管目前已有大量关于高原湖泊变化的研究，但高原湖泊水位变化过程及其如何响应两大气候系统变化仍不清楚。本项目拟对高原面上多个典型封闭湖泊水位进行连续观测，并结合区域降水、湖面蒸发和入湖径流的观测与模拟，分析西风、季风和季风边缘区湖泊水位变化过程的时空特征，探讨其与大气降水、湖面蒸发和入湖径流等主要影响因素的关系，揭示这些因素在不同气候区对湖水水位变化过程影响的差异；在更长时间尺度上，结合遥感资料分析1970年代以来西风和季风影响区高原湖泊变化过程的差异，探讨湖泊变化对大尺度环流变化的响应，揭示近期高原湖泊快速扩张的驱动机制。本项目的开展不仅对认识全球变暖背景下第三极地区水循环变化具有重要理论意义，同时对指导当地农牧民生产生活具有一定现实意义。

青藏高原湖泊众多，是亚洲水塔的重要组成部分。近十多年来高原内陆湖泊普遍出现快速扩张，对当地牧民生产生活和区域生态环境产生了一定影响。由于地处偏远，绝大多数高原湖泊缺少观测数据，极大限制了我们对高原湖泊水文过程的认识。本项目围绕青藏高原不同气候区湖泊水位变化过程以及对全球极端气候事件的响应这一科学问题展开。项目实施期间，我们陆续开展了高原季风区、西风区和过渡区15个湖泊水位观测，初步建成了高原湖泊水位监测网络。基于这些观测，我们主要开展了三个方面的研究工作。(1)青藏高原内陆湖泊的季节变化特征：发现高原湖泊存在两种截然不同的季节变化特征，高原西部湖泊水位表现出暖季和冷季均显著升高，与GRACE区域质量变化不一致，而其他区域湖泊表现出暖季升高而冷季下降，与GRACE区域质量变化有很好的一致性，反映了高原不同气候区流域尺度水循环的差异；(2)高原内陆湖泊的年际变化特征及其对极端气候事件的响应：发现2015年高原中部湖泊出现大范围干旱，湖水水位变化过程与正常年份存在显著差异，而2017和2018年高原湖泊出现极端扩张。进一步研究表明此次高原湖泊水位极端变化过程与2015年超级厄尔尼诺事件存在关联，ENSO事件的发生可以显著影响到高原中部的干湿变化；(3)高原典型湖泊的水量平衡特征：分析了高原南部佩枯错湖泊水量平衡过程，发现深水湖泊巨大的储热量导致湖面蒸发显著落后于净辐射达5个月，这进一步影响到湖水水位季节变化过程与幅度，使得湖水水位下降主要出现在秋冬季。我们在高原内陆区建立的湖泊水位变化和水量平衡监测网络不仅有助于理解高原湖泊扩张的水文过程，还对高原湖泊变化预测具有重要意义。相关成果发表后，科学网、中国科学报、青海新闻网等给予了报道。基于本项目开展的湖泊水位变化和水量平衡观测数据已经共享到青藏高原国家数据中心网站(http://en.tpedatabase.cn/data/lakelevel.jsp)。