西藏纳木错湖面蒸发与能量交换过程观测研究

There are numerous glaciers and lakes on the Tibetan Plateau. Glacier retreat has been accelerated in recent years due to global warming, which causes lake level increases and serious damage to local agriculture and animal husbandry. This is especially true in Naqu in the central Tibetan Plateau where large areas of quality grassland have been submerged. Therefore, it is necessary to study the water cycle processes of the glacer-lake systems and their response to the global change. As one of these key processes, evaporation over lakes of the Tibetan Plateau needs to be clarified. Although experiments of pan evaporation are carried out at some meteorological stations, direct and precise measurements of evaporation rate and energy exchange over lake surface have not been performed yet on the Tibetan Plateau. This project, backed up by the Nam Co Station of the institute of the Tibetan Plateau Research, Chinese Academy of Sciences, is designed to measure the evaporation and surface energy balance of Lake Nam Co using the eddy covariance (EC) method. The study is aimed to analyse the diurnal, seasonal and annual variations of evaporation and their major environmental controls, to reveal the characteristics of energy partitioning and exchange at the atmosphere-water interface of the lake, and further to develop a method of calculating the real lake evaporation based on the pan evaporation measurements and corresponding meteorological data. It is also designed to characterize the water and energy exchange between the lake and the surrounding land. The results would provide a solid basis for further studies on land surface processes and reconstructions of the environmental history of the Tibetan Plateau. They would also contribute to the local water resources management and development of the animal husbandry and agriculture.

青藏高原是湖泊和冰川集聚区。近年来，由于全球气候变暖，导致冰川消融增强，使湖泊水位发生较大变化，进而影响到青藏高原自然环境和农牧业生产，如那曲地区湖泊水位上涨淹没了大面积的优质草场。因此，迫切需要研究青藏高原冰川-湖泊系统水文与水循环过程。其中，湖泊蒸发是个重要环节，但目前还缺少研究，尤其是准确、直接测定湖面蒸发速率和能量交换过程的研究。本项目以中科院青藏所纳木错站为依托，通过采用涡动相关方法，得出纳木错湖面蒸发速率的日变化、季节变化和年变化及其主要控制因素；揭示湖面的能量分配与交换特征和湖水-大气相互作用过程；得出如何利用站测蒸发器观测资料和气象资料估算湖面实际蒸发量的方法；揭示湖陆之间的能水交换过程和特征。从而为进一步深入研究青藏高原地表过程和环境历史重建等奠定基础，并为青藏高原农牧业发展做出贡献。

青藏高原是湖泊和冰川集聚区。近年来，由于全球气候变暖，导致冰川消融增强，使湖泊水位发生较大变化，进而影响到青藏高原自然环境和农牧业生产，如那曲地区湖泊水位上涨淹没了大面积的优质草场。因此，迫切需要研究青藏高原冰川—湖泊系统水文与水循环过程。其中，湖泊蒸发是个重要环节，但目前还缺少研究，尤其是准确、直接测定湖面蒸发速率和能量交换过程的研究。本项目以中科院青藏所纳木错站为依托，通过采用涡动相关方法，研究纳木错的湖面蒸发量及其主要控制因素；揭示湖面的能量分配与交换特征和湖水—大气的相互作用过程；以及如何利用陆面气象资料准确估算出湖泊的蒸发量。研究得出纳木错2005-2014年非冻结期（5-11月）的日均蒸发量为2.8 mm，波动范围为0.6-8.0 mm。月均蒸发量为87 mm，波动范围为78-106 mm。非冻结期总蒸发量的10年平均值为608.7 mm，波动范围为564.7-662.5 mm。湖面与大气能量交换以潜热为主，月平均波文比Bo变化范围为0.07～0.73。从6月至11月，湖面感热通量和潜热通量呈逐渐增加趋势。6月至9月纳木错湖为热汇，从10月份开始逐渐转变为热源。纳木错湖总体上是个弱碳汇。其中，6-8月CO2通量值为正，是个碳源；10-11月CO2通量值为负，是个碳汇；9月份为转换期。此外，项目还利用气象观测数据优化了现有蒸发估算经验公式。这是首次在青藏高原内流区进行的湖面蒸发实测工作。研究结果是青藏高原水文和气象研究的重要参数，是准确估算内流区湖泊蒸发的重要依据。