克鲁伦河是中国和蒙古国重要的国际河流。进入二十一世纪以来，在全球气候变暖的大背景下，克鲁伦河流域水资源与生态环境面临严峻挑战。该流域干旱现象频发，河流干流流量减少，进而导致了中下游草原地区缺水、呼伦湖水位持续下降等问题。本文采用基于流域地貌特征的分布式水文模型GBHM，结合实测历史数据、遥感数据和未来NEX-GDDP-CMIP6数据集等，分析了克鲁伦河流域水文时空特征及干旱演变趋势。主要内容及成果如下：首先，在克鲁伦河流域构建了GBHM分布式水文模型，利用流域水文站点实测数据对模型进行了率定，并验证了模型的效果。通过纳什效率系数NSE等评价指标评估该模型的表现良好。然后，根据水文模拟结果，分析了历史1991-2020年间该流域各水循环要素的时空特性。结果表明，该流域水文要素具有较为明显的空间分界特征，上游区域是降水、蒸散发强度最高的区域，也是径流产生的主要区域；在年内分布上，夏季是该流域水文循环的主要活动时期。在时空变化上，该流域降水、实际蒸散发和径流深总体表现下降的趋势，气温总体表现上升趋势；其中上游流域的降水减少，导致径流深减少幅度较大，进而造成了河流流量的减少。最后，分析了未来SSP2-4.5情景下2021-2050年间流域的水文演变趋势和干旱特征。根据NEX-GDDP-CMIP6数据集和GBHM模型模拟结果，未来年降水量呈现减少的趋势，平均气温呈现出显著增加的趋势，年实际蒸散发和径流深受降水和气温影响呈现略微减少的趋势；在空间变化上，上游地区的降水有进一步减少趋势，气温和实际蒸散发有上升趋势，径流深也呈现出减少的趋势。未来三个站点巴嘎诺尔、温都尔汗和乔巴山控制流域及全流域上气象干旱和水文干旱的平均干旱强度会呈现出一定程度的减小趋势，但是气象干旱和水文干旱平均发生月数呈现较为明显的增加趋势。气象干旱和农业干旱在全流域的空间表现上，均呈现出上游地区频率增大、严重程度增加的趋势。
The Kherlen River is an important international river between China and Mongolia. Since the beginning of the 21st century, under the impacts of global climate warming, the water resources and ecological environment of the Kherlen River Basin have faced severe challenges. Droughts have become frequent in the basin, with reduced flow in the main stream of the river, leading to water shortages in the grassland areas of the middle and lower reaches, and continuous decline in the water level of Lake Hulun. This study utilizes the distributed hydrological model GBHM, combined with measured historical data, remote sensing data, and future NEX-GDDP-CMIP6 dataset, to analyze the hydrological spatiotemporal characteristics and drought evolution of the Kherlen River Basin. The main work and results are as follows:Firstly, the GBHM hydrological model was established in the Kherlen River Basin. The model was calibrated and validated using measured data from three hydrological stations on the main stream of the basin. Evaluation indices such as NSE indicated good performance of the model.Secondly, based on the hydrological simulation results, the spatiotemporal characteristics of various water cycle elements in the basin during the historical period from 1991 to 2020 were analyzed. The results showed that the hydrological elements of the basin exhibit obvious spatial characteristics. The upstream area is the region with the highest precipitation and evapotranspiration intensity, and also the main area of runoff generation. In terms of seasonal distribution, summer is the main period of hydrological cycle activity in the basin. In terms of the spatiotemporal changes, the basin‘s precipitation, actual evapotranspiration, and runoff depth generally show a downward trend, while the temperature shows an overall upward trend. Specifically, the decrease in precipitation in the upper reaches of the basin has led to a significant reduction in runoff , which in turn has caused a decrease in river flow.Finally, the future hydrological evolution trends and drought characteristics under the SSP2-4.5 scenario for the period from 2021 to 2050 were analyzed. According to the simulation results, future annual precipitation shows a slight decrease trend, while average temperatures show a significant increasing trend. Annual actual evapotranspiration and runoff depth show a slight decrease trend influenced by precipitation and temperature. In terms of spatial changes, there is a further decrease trend of precipitation in the upper basin, with increasing trends in temperature and actual evapotranspiration, and a decrease trend in runoff. The average drought intensity of meteorological and hydrological droughts in the three hydrological stations Baganuur, Undurkhaan, and Choibalsan control basins and the entire basin will show a certain degree of decrease in the future three sites. However, the average occurrence months of meteorological and hydrological droughts show a more significant increasing trend. Both meteorological droughts and agricultural droughts show trends of increased frequency and severity in the upstream region in spatial expression.
