自第一次工业革命以来，由于人类活动等原因，全球的气候和土地覆盖均发生了显著的变化，从而给全球、区域和流域尺度的水文循环带来了巨大的影响。“三北”地区是中国华北，东北以及西北地区的统称，是我国重要的生态脆弱区，覆盖了约一半的中国国土，且由东向西包括了湿润区，半干旱区及干旱区，气候分布较为多样。此外，为了遏制频繁的沙尘暴天气，中国政府曾在该地区实施了一系列的生态修复工程，再结合部分地区发生了迅速的城市扩张，“三北”地区的土地覆盖情况在过去数十年间发生了巨大的变化。由于“三北”地区的特殊性，很多科学家都针对过去数十年的水文循环响应开展了研究，但是对于未来的水文情势仍缺乏足够的预估。虽然也有一些针对未来水文响应的研究，但是大多数的研究在模拟未来的水文过程时，仅仅考虑了气候的变化，而假设土地覆盖在未来不会发生改变。 为了弥补当前研究的缺陷，本研究结合多种情景下的CMIP5未来气候数据和未来土地覆盖数据，使用大尺度分布式水文模型，对“三北”地区未来的水文情势进行了模拟预估。研究结果表明，气温和降水的变化主要与各排放情景下CO2排放量的变化相关，土地覆盖的变化则与人口扩张，技术革新等多个因素相关。利用温室气体的排放量以及化石能源的消耗，我们将气候变化情景与土地覆盖变化情景两两配对，生成参数后驱动陆面水文模型VIC模型。模拟结果表明，在不同排放情景下，“三北”地区整体的水文情势会发生不同的变化，且变化趋势主要与气候（气温和降水）的变化相关，如在高排放情景下，蒸发和产流会随着降水和气温的提升而稳定升高，而土壤湿度则会稳定降低。但是在局部土地覆盖变化比较明显的情况下，部分流域的水文变化趋势会与整体趋势出现差异，如在低排放和中低排放情景下其他流域的产流发生下降时，海河流域由于城市的扩张，产流反而会出现升高的情况。总体来说，未来“三北”地区东部湿润地区可能会受到洪涝灾害的威胁，而西部干旱地区有继续干旱的可能性。尽管该研究中存在一些不足，但研究结果依然能为“三北”地区未来各种情况下可能面临的威胁提供一个新视角。在未来，为了能够更加准确地模拟该区域水文循环演变，可能需要更高时空分辨率和精度的未来气候，土地覆盖以及植被数据。

Since the first Industrial Revolution, the global climate and land cover both have experienced significant changes due to human activities, which have greatly influenced the global , regional, and basin-scale hydrological cycle. The Three North Region is an important ecological fragile region of China, covering nearly half of the country, and including humid areas, semi-arid areas, and arid areas. Besides, to combat the frequent sand storm weather, the Chinese government has launched a series of ecological restoration programs. Because of those programs and rapid urban expansion, the land cover condition has changed significantly over this region. Many studies have been conducted to explore the hydrological effects of climate change and land cover change, and some of them also predicted future hydrological regimes under different climate scenarios. However, most of them only considered the changing climate, while assuming that the land cover condition will keep unchanged in the future. In this study, we employed a large scale hydrological model, with predicted climate datasets and land cover maps under different scenarios, to simulate the future hydrological processes over the Three North Region. The results show that the changes in temperature and precipitation will be highly related to those in the emission of CO2, while the land cover will be affected by population growth, technological innovation and other factors. According to the consumption of the energy and the emission of the CO2, we linked the scenarios of climate change and land cover change, then generated the parameters to force the model. The results of simulations show that the regional hydrological regimes would experience various changes under different scenarios, and mainly controlled by climate. For example, under the highest emission scenario, with the growth in temperature and precipitation, the evapotranspiration and runoff will rise steadily, and the soil moisture may decline. However, in some areas where the land cover changed greatly, the hydrological regimes may experience different changes. For instance, under low emission scenario, when the runoff in other basins would decrease, that in Hai River Basin may increase because of the urban expansion. In addition, the humid area in the east may be threated by floods, and the arid area may be drier in future. Although there are still some limitations in this study, the results can still provide a new insight into the problems we may face over this region. In the future, to simulate the projected hydrological cycle more precisely, the predicted climate, land cover and vegetation datasets with a higher temporal-spatial resolution and precision will be needed.