## 1 Introduction
[15] conducted a quantitative study of the relationships among soil, groundwater depth, and vegetation in terms of how these relationships have implications for EQ changes and found that the community cover, community height, leaf projection cover, and leaf area index (LAI) had all decreased significantly with increasing groundwater depth. [PERSON] et al. [16] analyzed the different ecosystems of Inner Mongolia to which different grazing ban policies applied and found that the trend of positive influences of precipitation on these ecosystems had begun to weaken because of overgrazing. [PERSON] et al. [17] analyzed the effect of different vegetation-change scenarios on ET in the Mongolian Plateau and discovered that ET increased with an improvement in vegetation. It was also found that changes in terrestrial ecosystem quality are strongly related to the relevant hydrological process factors such as precipitation, ET,and groundwater [18; 19; 20]. However, most of the existing studies have focused on the relationship between singular hydrological process factors and ecosystems. The research on the synergistic evolution of overall hydrological processes and ecosystems in arid and semi-arid regions is scarce. Located in XilinGol League, Inner Mongolia, China, the Ulagai River Basin (URB) is a typical inland river basin in an arid and semi-arid region. As the second largest inland river basin in China, it is also an important livestock base and green ecological barrier [20]. The URB is subject to natural conditions and has a fragile ecological system, which is particularly sensitive to changing environmental conditions [21]. Due to climate change causing an increase in precipitation, temperature, and ET and the continuing influence of reclamation, irrigation, and grazing, a gradual increase has been observed in water shortage, river disruption, sanding of grasslands, and salinization in the URB. This poses a great threat to extant water resources and ecological balance in arid and semi-arid regions [21; 22]. Moreover, some studies have shown that arid and semi-arid regions, such as the Mongolian Plateau, may experience more pronounced rises in temperature and more frequent droughts, leading to further water scarcity and deteriorating EQ [23; 24]. Against the backdrop of global warming and the impact of human activities, the synergistic evolution of hydrological processes and EQ in the URB needed to be analyzed, for such an analysis could provide a basis for the conservation of water resources and sustainable ecological development of inland river basins in arid and semi-arid regions. Although some progress has been made in the study of a certain hydrological process factor and ecosystem, relatively few studies have been conducted on the synergistic relationship between the whole hydrological cycle process and EQ. Specifically, this study aimed to achieve the following: characterize the evolution of the hydrological process factors in the inland river basins of arid and semi-arid regions from 2001 to 2019; comprehensively evaluate EQ of inland river basins in arid and semi-arid zones from 2001 to 2019; and explore the characteristics and differences in the synergistic evolution of the hydrological process factors and EQ in different river sections in the inland river basins of arid and semi-arid zones. The findings of this study can deepen the awareness of eco-hydrorological processes and evolution patterns in semi-arid inland river basins, thereby providing an empirical basis for the sustainable use of water resources and ecological protection in semi-arid inland river basins.