水资源是重要的基础性自然资源和环境资源，在水文循环中气候、植被、土壤以及人类活动都可以对径流产生影响。近年来，全球气候变化改变了区域水热条件，“退耕还林还草”和“三北防护林”等重点工程改变了地表植被覆盖，黄河流域内蒙古段是中国北方重要的生态屏障，水资源短缺和生态环境问题突出，在气候变暖和人类活动的背景下，该区的生态水文过程发生改变，各因素对径流变化的影响程度也存在着诸多不确定性。因此本文以黄河流域内蒙古段为研究区，识别气候与植被变化的径流效应。本研究基于数学统计方法Copula函数，研究黄河流域内蒙古段气候与植被协同变化对径流的影响。在研究区典型小流域浑河流域开展VIC模型建立工作，实现典型小流域水文要素的精确模拟，并分别量化气候变化和人类活动对于水文要素（径流、蒸散发、土壤水）的贡献，设定不同的气候、植被变化情景，研究水文要素对变化环境的响应机制，利用CMIP6数据输入模型预测小流域未来径流变化，为流域水资源保护和可持续发展提供理论依据，主要结论如下：

（1）过去40年间黄河流域内蒙古段气温升高、降水微弱升高，潜在蒸散发量呈上升趋势，流域水文干旱（SRI）和气象干旱（SPEI）均呈现持续加剧的局面，表明该地区水资源存在供需矛盾。受人类活动影响，1985-2020年黄河流域内蒙古段大面积耕地、裸地转为草地，NDVI、LAI呈明显上升趋势，表明该流域退耕还林、还草政策效果显著。

（2）1982-2020年黄河流域内蒙古段年均NDVI、挡阳桥水文站突变点均在1999年，据此将研究期划分为基准期(1982~1999年)、变化期(1999-2020年)。利用 Copula 函数在黄河流域内蒙古段构建了降水-NDVI-径流、降水-LAI-径流间联合分布及条件分布，发现2000年前后气候-植被指数-径流联合分布结构差异明显，随着累计概率的增加，黄河流域内蒙古段降水的变化量逐渐增大，NDVI、LAI的变化量也呈增加趋势，径流量减少的变化也逐渐显著。随着植被覆盖度上升，区域径流相应减少，满足相同产流需要的降水量明显增加。

（3）浑河流域是研究区内植被显著恢复的典型小流域，该流域NDVI序列的突变点也在1999年，将其作为研究区典型小流域建立VIC模型，利用实测径流数据、遥感蒸散发数据进行参数率定和验证，结果表明VIC不仅适用于浑河流域径流模拟，也适用于其他水文要素的模拟。气候变化和人类活动对研究区年径流量减少的贡献率分别为13.4%和86.6%，对蒸散发增加的贡献率分别为27.9%和72.1%，对浑河流域土壤含水量增加的贡献率分别为75.4%和24.6%。人类活动对于所有月份的径流都具有负效应，尤其降低了汛期径流；气候变化并不对所有月份的径流都有负效应，主要使春季和冬季径流量减少。总之，相较于基准期，人类活动是浑河流域变化期径流量减少、蒸散发增加的主导因素，气候变化是浑河流域土壤含水量增加的主导因素。

（4）浑河流域径流、蒸散发对降水增加的敏感性均要强于降水减少，当降水增加时，径流的增加率远高于降水的增加率。气温升高会减少浑河流域径流量和土壤含水量，增加蒸散发量，在高值降水时流域径流对气温的变化更为敏感。在控制外部条件一致的情况下，耕地、林地转变为草地、以及林地转化为耕地将增加径流量，反之则减少径流量。当草地转化为林地、耕地转化为林地、草地转化为耕地时，蒸散发量增加，反之蒸散发量减少。浑河流域当草地向耕地转变、林地向耕地转变、林地向草地转变时会引起土壤含水量升高，反之会使土壤含水量降低。利用CMIP6气象数据输入VIC模型，预测2015-2100年浑河流域径流量，发现未来情景下浑河流域降水和气温均呈增加趋势，其中SSP5-8.5情景下气温、降水增加趋势最为显著，2015-2100年模拟的浑河流域径流量呈上升趋势，且SSP5-8.5情景下径流增加最为显著，表明了径流增加与降水增加紧密相关。

Water resource is an important basic natural and environmental resource. In the hydrological cycle, climate, vegetation, soil and human activities can all affect runoff. In recent years, global climate change has changed regional water and thermal conditions, and key projects such as "returning farmland to forest and grassland" and "Three-North Shelterbelt" have changed the surface vegetation cover. The Mongolian section of the Yellow River Basin serves as a vital ecological barrier in northern China, lying within the semi-arid landscape, and the shortage of water resources and ecological environment problems are prominent. Under the background of climate warming and human activities, the ecohydrological process in this area has changed. There are also many uncertainties about the influence degree of each factor on runoff change. Therefore, this study focuses on the Inner Mongolia section of the Yellow River Basin as its research area to identify the runoff effect of climate and vegetation change. Based on the Copula function, a mathematical statistical method, the collaborative change of climate and vegetation on runoff in the Mongolian section of the Yellow River Basin was studied. In Hunhe Basin, a typical small watershed in the study area, VIC model was established to achieve accurate simulation of hydrological elements in typical small watershed, and the contributions of climate change and human activities to hydrological elements (runoff, evapotranspiration, soil water) were respectively quantified, different climate and vegetation change scenarios were set up, and how hydrological elements respond to environmental changes. It provides a theoretical basis for the protection and sustainable development of water resources in the basin. The main conclusions are as follows:

(1) In the past 40 years, the temperature and precipitation of the study area increased slightly, the potential evapotranspiration showed an upward trend, and the hydrological drought (SRI) and meteorological drought (SPEI) in the basin continued to intensify, indicating the discrepancy between water resource demand and supply in this region. From 1985 to 2020, a large area of cultivated land and bare land in the Mongolian section of the Yellow River Basin was converted to grassland, and NDVI and LAI showed an obvious upward trend, indicating that the policy of returning farmland to forest and grassland in the basin was effective.

(2) The average annual NDVI and the abrupt change points of the hydropower station in the Inner Mongolia section of the Yellow River Basin during 1982-2020 were both in 1999, so the study period can be divided into the base period (1982-1999) and the change period (1999-2020). The Copula function was used to construct the joint distribution and conditional distribution of precipitation -NDVI- runoff and precipitation - LAI-runoff in the Mongolian section of the Yellow River Basin. It was found that the joint distribution structure of climate-vegetation-runoff was significantly different before and after 2000. With the increase of the joint cumulative probability, the variation of precipitation in the study area gradually increased. The changes of NDVI and LAI also showed an increasing trend, and the decrease of runoff was also gradually significant. With the increase of vegetation, the regional runoff decreases correspondingly, and the precipitation distribution range becomes larger, and the precipitation to meet the same flow production needs increases significantly.

(3) Hunhe Basin is a typical small watershed with significant vegetation recovery in the study area, and the mutation point of NDVI series in this basin was also in 1999. The VIC model was established as a typical small watershed in the study area, and parameter calibration and verification were carried out using measured runoff data and remote sensing evapotranspiration data. The results showed that VIC was not only suitable for runoff simulation in Hunhe basin, but also for runoff simulation. It can also be applied to the simulation of other hydrological elements. The contribution rates of climate change and human activities to the decrease of annual runoff are 13.4% and 86.6%, the increase of evapotranspiration is 27.9% and 72.1%, and the increase of soil water content is 75.4% and 24.6%, respectively. Human activities have negative effects on runoff in all months, especially on runoff in flood season. Climate change does not have a negative effect on runoff in all months, mainly reducing runoff in spring and winter. In conclusion, human activities are the main factors of runoff reduction and evapotranspiration increase in Hunhe Basin, and climate change is the main factor of soil moisture increase in Hunhe Basin.

(4) The sensitivity of runoff and evapotranspiration to precipitation increase is stronger than that of precipitation decrease in Hunhe Basin. When precipitation increases, the increase rate of runoff is much higher than that of precipitation. The increase of temperature will reduce the runoff and soil water content, increase the evapotranspiration, and the runoff is more sensitive to the change of temperature in the Hunhe basin when the precipitation is high. Under the control of the same external conditions, the conversion of cultivated and forest land to grassland, and forest land to cultivated land will increase the runoff, and vice versa. The evapotranspiration increases when the grassland is converted to forest land, the cultivated land is converted to forest land, and the grassland is converted to cultivated land, whereas the evapotranspiration decreases. The change from grassland to cultivated land, forest land to cultivated land and forest land to grassland in Hunhe Basin will lead to the increase of soil water content, and vice versa. CMIP6 meteorological data was input into VIC model to predict the runoff of Hunhe Basin from 2015 to 2100. It was found that both precipitation and temperature showed an increasing trend in the future, among which SSP5-8.5 temperature and precipitation showed the most significant increasing trend. The simulated runoff of Hunhe Basin from 2015 to 2100 showed an increasing trend. In the SSP5-8.5 scenario, the runoff increase was the most significant, indicating that the runoff increase was closely related to the precipitation increase.