冻土是冰冻圈的重要组成成分，在全球气候变暖的影响下会发生退化。青藏高原作为中低纬度面积最大、海拔最高的冻土区，冻土温度相对较高、厚度较薄、热稳定性差。在全球气候变暖背景下，青藏高原冻土显著退化，进一步影响区域水文过程。因此分析青藏高原冻土分布变化及其产生的水文效应，对于科学研究和生态环境保护具有重要意义。
由于青藏高原气候恶劣，实测冻土数据获取困难，冻土分布模型成为了解青藏高原冻土分布情况的有效手段。本论文基于气象观测及遥感数据，选取高程模型、年平均地温模型、冻结数模型、多年冻土顶板温度模型（TTOP模型）共四种经验统计模型和陆面过程模型The Community Noah Land Surface Model with Multi-parameterization Options（Noah-MP）对青藏高原冻土分布进行时空变化模拟。通过与前人编制冻土图件对比以及各个模型间对比，评估各模型模拟结果表现出的趋势和范围一致性，分析冻土分布变化特征。在此基础上选取长江源区、黄河源区作为典型区域，使用多种方法对于气象、水文要素进行分析，探究冻土退化产生的水文效应。
研究结果表明：四种经验统计模型的模拟结果均表明青藏高原多年冻土面积整体呈现退化趋势。冻结数模型多年平均退化速率为1.19×104 km2/a，TTOP模型多年平均退化速率为1.68×104 km2/a。多年冻土退化主要发生在区域西南部的雅鲁藏布江地带、中部的巴颜喀拉山脉等区域。其中高程模型因未考虑其他局部因素可能会高估研究区的多年冻土范围，冻结数模型和TTOP模型模拟结果最为相似。
Noah-MP模型的模拟结果表明青藏高原全域表层冻土面积呈现明显的下降趋势，平均退化速率为1.05×104 km2/a。Noah-MP模型的输出变量分析结果表明，青藏高原全域2 m深度内的年平均地温呈现明显的上升趋势，平均每年上升0.038 ℃。土壤温度的上升导致青藏高原地区土壤液态水和土壤冰含量发生变化。在模拟时间段内，青藏高原全域土壤冰含量整体呈现波动下降趋势，平均每年减少1.82亿吨；土壤液态水含量整体呈现波动上升趋势，平均每年增加6.78亿吨；地表径流量、地下径流量整体呈现波动上升趋势，平均每年分别增加19.73亿吨、17.99亿吨。
长江源区年降水、气温、潜在蒸散发、径流量均呈现增长趋势，冻土面积发生突变的时间点在1998年，与气象及水文要素的变化相一致。黄河源区气温、潜在蒸散发呈现增长趋势，径流量减少，冻土面积发生突变的时间点与气温的变化相一致。
 

Permafrost is an important constituent of the cryosphere and sensitive to climate change. As the largest permafrost area with the highest altitude in the middle and low latitudes, the Qinghai-Tibet Plateau(QTP) has relatively high permafrost temperature, thin thickness and poor thermal stability. In the context of global warming, the permafrost on the QTP is significantly degraded, which further affects the regional hydrological processes. Therefore, it is important to study the spatial distribution of permafrost and the hydrological effects of permafrost degradation on the QTP.
Based on meteorological and remote sensing data, this thesis selects a total of four empirical statistical models: Elevation model, Mean Annual Ground Temperature (MAGT) model, Freezing Index model, The Top Temperature Of Permafrost model(TTOP) and land surface process model The Community Noah Land Surface Model with Multi-parameterization Options(Noah-MP) model to simulate the spatial and temporal changes of permafrost distribution on the QTP. They are also compared with the previously prepared maps to assess the applicability of each model on the QTP and analyze the change characteristics of permafrost distribution. On this basis, the source area of the Yangtze River and the source area of the Yellow River were selected as typical areas, and the meteorological, hydrological elements were analyzed using M-K tests to investigate the hydrological effects of permafrost degradation. 
The results of the study show that the simulation results of the four empirical statistical models indicate an overall degradation trend of the permafrost area on the QTP. The average degradation rate of the Freezing Index model is 1.19×104 km2/a and the average degradation rate of the TTOP model is 1.68×104 km2/a. Permafrost degradation mainly occurs in the Yarlung Zangbo River in the southwest and the Bayan Kara Mountains in the central part of the region. The Elevation model may overestimate the extent of permafrost in the study area because other local factors are not taken into account, and the simulation results of the Freezing Index model and TTOP model are the most similar.
The simulation results of the Noah-MP model show that the permafrost area of the entire QTP shows an obvious decreasing trend, and the average degradation rate is 1.05×104 km2/a. Among them, the permafrost area in the endorheic zone is the most widely distributed, and the permafrost area in the Yellow River basin is the least distributed. The output variable analysis results of the Noah-MP model show that the annual average ground temperature at 2m depth across the QTP shows a significant increasing trend, with an average increase of 0.038 °C per year. The increase in soil temperature leads to changes of soil liquid water and soil ice in the QTP. During the simulated time period, the soil ice content of the entire QTP showed an overall fluctuating decreasing trend, decreasing by 1.82 billion tons per year on average; the soil liquid water content showed an overall fluctuating increasing trend, increasing by 6.78 billion tons per year on average; the surface runoff and underground runoff showed an overall fluctuating increasing trend, increasing by 1.973 billion tons and 1.799 billion tons per year on average, respectively.
The annual precipitation, temperature, potential evapotranspiration, and runoff in the source area of the Yangtze River show an increasing trend, and the sudden change of permafrost area occurred in 1998, which is consistent with the changes of meteorological and hydrological elements. In the source area of the Yellow River, the temperature and potential evapotranspiration show an increasing trend, and the runoff decreases, and the sudden change of permafrost area is consistent with the change of temperature.