青藏高原被称作世界第三极，广泛分布着多年冻土；由于发源了众多亚洲重要河流，也被称作亚洲水塔。青藏高原的水储量变化及其固/液态转化影响着这些河流源区的径流过程，进而影响到河流中下游地区的水资源利用和水资源安全。青藏高原冻土区不仅有大量的地下冰，也储存了大量土壤有机碳，冻土融化释放温室气体可能改变区域碳收支，进而影响气候。因此，开展青藏高原冻土变化及其水碳效应研究具有重要的科学意义和应用价值。 本论文首先基于观测数据分析了青藏高原历史气象冻土要素变化，然后构建了适用于青藏高原的冻土模型，包括基于物理机理的分布式冻土水文模型GBEHM，以及基于机器学习算法的冻土模型；采用数值模拟方法重现了青藏高原长序列、高分辨率（1 km×1 km）的冻土水文过程变化，基于模拟结果评估了冻土变化对水文过程与区域碳收支的影响，得出如下主要结论： （1）在1980~2019年间，青藏高原的气候呈暖湿化趋势，年均气温以0.045 °C/a的速率升高，年降水以1.09 mm/a的速率增加；多年冻土面积从120.5万km2下降到了110.9万km2，下降幅度为7.9%，还有7.5%的多年冻土范围出现了融化夹层；季节性冻土最大冻结深度减小速率为0.85 cm/a，多年冻土活动层厚度增加速率为0.90 cm/a。在RCP 4.5情景下，预估至2040、2090年代多年冻土面积将下降25.9%、43.9%，季节性冻土最大冻结深度继续减小，多年冻土活动层厚度持续增加。 （2）在过去40年间，青藏高原的年蒸散发量与年径流量均显著增加，增加速率随高程升高而增大；地下冰储量减少约282 km3（7.7%），总地下水储量呈增加趋势。结合模型数值试验，青藏高原地下冰融化对径流的贡献率在0.5%~1.7%范围内，与冰川融化对径流的贡献率接近。 （3）青藏高原多年冻土区的土壤有机碳储量约为50.43 Pg（不确定性范围35.78~69.02 Pg）。从基准期（2006~2015年）到2090年代，冻土融化释放的可供分解的有机碳累积将达1.86 ± 0.49 Pg（RCP 4.5）或3.80 ± 0.76 Pg（RCP 8.5）；随着时间推移，从深层冻土中融化的有机碳越来越多。冻土融化导致的碳释放将可能使青藏高原多年冻土区从净碳汇变为净碳源。 本论文的研究成果为今后进一步深入探讨气候变化下青藏高原生态环境演变与亚洲水塔水循环水资源变化打下了基础。

The Tibetan Plateau, known as the world’s third pole, is widely underlain by permafrost. As the source of many major Asian rivers, it is also called the Asian Water Tower. The changes in the water storage and its transition from solid to liquid phase influence the hydrological processes of these headwater regions, thus affecting the water resources utilization and security in the midstream and downstream regions. In addition to the large amount of ground ice stored in the Tibetan Plateau permafrost region, there also exists a large quantity of soil organic carbon. The greenhouse gas emissions due to permafrost thawing could alter the regional carbon budget and impact the climate. Therefore, research on frozen ground change and its impacts on hydrological and carbon cyble over the Tibetan Plateau is of great scientific significance and application value. This study first analyzed the historical changes in meteorological and frozen ground variables over the Tibetan Plateau according to the observations, and then established the frozen ground models suitable for the Tibetan Plateau, including the physically-based distributed permafrost-hydrological model GBEHM, and the frozen ground models based on machine learning algorithms. Through numerical simulation methods, long-term high-resolution (1 km×1 km) variations in frozen ground and hydrological processes on the Tibetan Plateau were reproduced. Based on the simulation results, the responses of hydrological processes and regional carbon budget to frozen ground change were assessed. The following main conclusions have been reached: First, during 1980~2019, the Tibetan Plateau experienced a warming and wetting trend. The mean annual air temperature rised by 0.045 °C/a, and the annual precipitation increased by 1.09 mm/a. The permafrost area dropped from 1.205 million km2 to 1.109 million km2, indicating a 7.9% decline, and taliks formed in 7.5% of the permafrost area. The maximum thickness of seasonally frozen ground decreased at a rate of 0.85 cm/a. In the meanwhile, the permafrost active layer deepened at a rate of 0.90 cm/a. By 2040s or 2090s, the permafrost area is projected to decrease by 25.9% or 43.9% under RCP 4.5 scenario; meanwhile, the maximum thickness of seasonally frozen ground is predicted to keep decreasing, and the active layer of permafrost is predicted to further deepen. Second, annual evapotranspiration volume and annual runoff volume increased significantly during the past 40 years, and more rapid increases took place at higher elevations. During 1980~2019, the ground ice storage over the Tibetan Plateau decreased by around 282 km3 (7.7%), and the total ground water storage showed an increasing trend. According to the results from model numerical experiments, the contribution of ground ice melt to runoff is estimated to be in the range of 0.5%~1.7% over the Tibetan Plateau, which is close to the contribution of excess glacier melt to runoff. Third, the soil organic carbon storage over the Tibetan Plateau permafrost region is estimated to be around 50.43 Pg (uncertainty range, 35.78~69.02 Pg). The cumulative amount of organic carbon vulnerable to decomposition due to permafrost thawing is projected to be 1.86 ± 0.49 Pg (RCP 4.5) or 3.80 ± 0.76 Pg (RCP 8.5) from the baseline period (2006~2015) to the 2090s, and the thawed organic carbon from deeper layers is predicted to increase with time. The carbon release due to permafrost degradation could offset the carbon sink of the Tibetan Plateau permafrost region, and even possibly change the region into a net carbon source. The results of this study provide basis for future research on the eco-environmental evolution over the Tibetan Plateau and the changes in water cycle and water resources of the Asian water tower in a changing climate.