西藏羊卓雍错湖泊水量变化过程模拟研究

In the Tibetan Plateau, there are many lakes and glaciers, which have been changing significantly in recent years. Limited by the observation data and research methods, the major factor inducing the expansion and/or contraction remains unknown for most of the lakes in the Tibetan Plateau. This project takes the Yamzhog Yumco, the largest lake in South Tibet, as an example, uses a distributed hydrological model (WEB-DHM) and a lake model (FLake) to simulate the lake water changes based on field observation and remote sensing data: 1) the precipitation over the lake and precipitation distribution over the basin will be determined based on the precipitation at meteorological stations and an observation network established by the research group; 2) the runoff will be simulated for glacier and non-glacier sub-basins and the whole basin through calibration of the hydrological model using runoff observation and remote sensing data such as albedo etc; 3) the lake model will be built to simulate and analyze the lake evaporation through calibration of lake water temperature measurements and the lake surface temperature remote sensing data; and 4) historical power generation data will be used to estimate water consumption by the Hydropower Station, and comprehensive analysis based on lake water level, precipitation, glacier melt - snow melt - rainfall runoff, lake evaporation and water consumption will identify the contribution rate of individual water balance factors to the lake water volume changes during the last four decades. The objectives are to understand the responding mechanism of plateau lakes to climate change and human activities, and to provide scientific support for grassland planning and power station operation in the lake basin.

青藏高原湖泊、冰川众多，近年来变化显著。受资料和研究手段限制，目前对大多数湖泊扩张或萎缩的主导因子认识不足。本项目拟以藏南最大内陆湖羊卓雍错为例，以分布式水文模型（WEB-DHM）和湖泊模型（FLake）为研究手段，综合利用地面和遥感观测数据，开展湖泊水量变化模拟研究：1）基于气象站和本课题组已布设的降水观测网，确定湖面降水及流域水分输入；2）利用水文站多年径流数据和反照率等遥感数据，对冰川和非冰川子流域径流模拟进行校验，进而模拟分析流域融冰-融雪-降雨径流补给；3）开展湖水剖面温度观测，结合湖面温度遥感数据对湖泊模型进行校验，模拟分析湖面蒸发；4）利用羊湖电站历史发电量估算用水量，结合湖水水位、降水、融冰-融雪-降雨径流和湖面蒸发量，综合分析过去40年各水量平衡要素对湖泊水量变化的贡献率。从而进一步认识高原湖泊变化对气候变化和人类活动的响应机制，并为湖区的草场规划、电站运行提供科学依据。

青藏高原湖泊众多，近年来发生显著变化。受资料和研究手段限制，目前对大多数高原湖泊水量变化的主导因子认识不足。本项目选取高原南部的典型冰川补给湖泊羊卓雍错为研究对象，整合气象水文、卫星遥感、湖温观测、电站发电量等多源数据，利用J2000分布式水文模型模拟、FLake湖泊蒸发模型模拟和水量平衡计算，定量分析了羊卓雍错过去40年湖泊水量平衡关键要素的变化，解析了各要素对湖泊水量变化的贡献率，揭示了湖泊变化对气候条件和人类活动的响应。主要研究发现如下：1）羊卓雍错水位在过去40年呈现波动减少的趋势，年内最高水位出现在9-10月、最低水位出现在6月。2）利用基于梯度校正的流域降水驱动水文模型，模拟入湖径流，结果显示降雨、融冰、融雪径流和基流的平均占比分别为51.5%、14.1%、1.6%和32.8%，夏季、秋季、冬季和春季径流量分别占年径流量的59.0%、24.8%、8.2%和7.9%。3）监测数据显示湖温在4-10月出现温跃层，利用实测湖温廓线校验湖泊模型，模拟得到的湖面蒸发量多年平均值为1161.9 mm，且年内湖面蒸发量高值出现在秋季。4）1975-2017年间，流域气温、总径流和降雨径流分量呈显著上升趋势，降水和融冰径流分量呈不显著增加趋势，融雪径流和湖面蒸发呈不显著下降趋势；（5）1975-2017年间，湖泊年均补给水量为8.2亿m3/a，其中湖面降水量、降雨径流量、融冰径流量、融雪径流量和基流量分别占31.2%、32.7%、7.0%、1.1%和28.0%，湖泊年均损耗水量为8.9亿m3/a，其中湖面蒸发量和发电用水量分别占90.3%和9.7%。5）降水、蒸发、气温变化和发电用水分别能解释1975-2017年间湖水累积减少量的-27.3%、-34.9%、-47.9%和210.1%，即降水量的增加、蒸发量的减少和温度升高造成的冰川融水增加抵消了一部分发电用水导致的湖泊水量减少。6）从羊卓雍错生态环境保护和恢复的角度，建议暂停羊湖电站发电，后期应根据气候变化影响动态调整发电量。本项目的研究成果可为数据匮乏条件下青藏高原湖泊变化研究提供可参考的实例，为湖泊流域的水资源管理和生态保护提供科学参考。