怒江流域中上游水文过程对土壤冻融循环变化的响应机制

As a result of climate change, soil freeze-thaw cycle in Qinghai-Tibetan Plateau has varied significantly. The responses of hydrological processes to soil freeze-thaw cycle variations in major watershed are important to understand the evolutions of hydrological cycle and water balance in Qinghai-Tibetan Plateau, while the deficiency of continuous and long-term surface freeze-thaw states and land surface temperature data in a wide range has restricted its study. In this research, the upper and middle Nujiang River Basin with significant climate warming, permafrost degradation, and low flow variation, was selected as research area. Remote sensing data would be combined with ground observation data to analyze the spatial-temporal variation characteristics and influence factors of freeze/thaw states, and also the relationships between freeze-thaw cycles and flow variations. Making use of surface freeze/thaw states and land surface temperature retrieved from remote sensing, and improving the modules of infiltration, soil water, and evapotranspiration to develop distributed hydrological model, which would be appropriate for plateau mountainous environment influenced by soil freeze–thaw cycle. Researching on the responses of hydrological processes to soil freeze–thaw cycle variations in major watershed in Qinghai-Tibetan Plateau, and the results could provide some references for water resources utilization, ecological and environmental conservation, and sustainable social and economic development.

在气候变化背景下，青藏高原土壤冻融循环过程发生了明显改变。明晰大河流域水文过程对土壤冻融循环变化的响应机制，对于理解青藏高原水循环和水量平衡的演化具有重要意义，然而大范围、连续、高时间分辨率地表土壤冻融状态及地表温度数据的缺乏，却在很大程度上对此形成制约。本研究拟以气温快速上升、冻土退化明显、枯季径流变化显著的怒江流域中上游作为研究区，结合遥感与地面观测数据，多尺度揭示流域地表冻融状态时空分异特征及其影响因素，以及地表冻融循环与径流变化的关联特征；利用遥感反演得到的地表冻融状态及地表温度数据，对下渗、土壤水、蒸散发等模块进行改进，构建适合高原山地流域、土壤冻融循环影响的流域分布式水文模型；判识气候变化背景下，青藏高原大河流域水文过程对土壤冻融循环改变的响应机制，为水资源合理利用、生态环境保护以及区域社会经济可持续发展提供依据。

在气候变化背景下，青藏高原土壤冻融循环过程发生了明显改变。明晰大河流域水文过程对土壤冻融循环变化的响应机制，对于理解青藏高原水循环和水量平衡的演化具有重要意义。本项目开展了这些方面的研究：（1）结合遥感与地面观测数据，多尺度揭示怒江流域中上游地表冻融状态时空分异特征及其影响因素，研究区气温的年际波动导致地表冻结面积、冻结日期、融化日期及冻结持续时间等的年际变化。（2）构建适合高原山地流域、土壤冻融循环影响的流域分布式水文模型，在枯水及洪水期怒江流域上中下游的模拟中均取得了较好的效果。（3）判识青藏高原大河流域水文过程对土壤冻融循环改变的响应机制。地表冻融时间的年际变化影响了径流形成过程。当地表较早冻结时，更多土壤水被保存在冻结层中，导致地表径流和壤中流的减少；当地表冻结较晚时，9至10月地表径流和壤中流受冻结过程的影响则较小。在消融阶段，当气温相对较低，冻土消融较晚，降水或融雪产生的水量难以下渗，更多地以地表径流的方式产流。通过本项目的研究，揭示了高原山地环境水文过程对冻融循环变化的响应规律，厘清了其变化的归因并阐明其关键作用机制；多尺度辨识怒江流域水文过程及其地域分异规律，为该流域水资源合理利用及生态环境保护提供依据。