## 1 Introduction  
The Earth critical zone (ECZ), proposed by the National Research Council of the United States in 2001 [1], is a complex combination of geology, geochemistry, biology, hydrology, landforms, and atmospheric processes. Research on the ECZ is flourishing in a globally coordinated environment [2], which is currently a major topic of geoscience based on systematic principles. The natural geographical environment, human social behavior, and ecological service effects are unified by ECZ in this dynamic system, that is, the key belt of the earth integrates the structure-pattern-function of the system. The atmosphere-soil circle-hydrosphere-lithosphere is integrated and resolved by this critical region, in other words, ECZ is the spatial bond of these four layers [3, 4]. Groundwater is the boundary between the soil layer and the rock layer in ECZ. It is not only a buffer zone for underground soil and rock, but also frequently interacts with energy on the ground [5]. As an inseparable part of the earth's key water cycle, groundwater undertakes a variety of ecological service functions such as flood storage and replenishment, water conservation, soil conservation [6; 7; 8; 9; 10; 11], and maintains the balance and stability of the underground ecosystem. As an undercurrent runoff that cannot be directly measured, groundwater is different from surface runoff, surface runoff is easy to analyze. The convergence and recharge processes of groundwater are quite different in multiple environmental modes [12; 13; 14]. Changes in groundwater often cause imbalances and damage to the stability of the entire ecosystem. At present, the excessive exploitation of groundwater in China has caused a dramatic drop in the groundwater level, which is a comprehensive reflection of hydrogeological elements, including the changes in groundwater recharge, runoff, excretion, as well as the environmental problems of groundwater and its severity. The shallow groundwater level has also dropped drastically, the original swamp wetlands have been drained, the original oasis has become a bare ground, and the landscape has been destroyed [15]. All of these issues have caused great damage to the buffer zone of the ECZ, which seriously affects the stability and self-healing ability of the ECZ [16; 17]. The groundwater volume could quantitatively reflect its characteristics--the change of groundwater depth is the most direct manifestation of the amount of groundwater, and thus, is the most important control indicator of groundwater management [18]. Wengniute Banner is one of the severe water-deficient areas in Inner Mongolia. The water-deficient and ecologically fragile area accounts for more than 30% of the city's total area and is a typical research area for key agricultural and pastoral zones (KAPZs) [19; 20]. Due to specific natural geography and hydrogeological conditions, groundwater has always been an important source of water for the Wengniute Banner and played an important role in the development of the regional economy [19; 20; 21; 22; 23]. However, severe water shortage, coupled with long-term over-exploitation and a lack of groundwater resources has become an ecological \"bottleneck\" that constrains regional economic development [22]. Most researchers study the groundwater distribution mainly through two approaches. The first approach is the model mechanism for simulating the collection and convergence process of groundwater, such as the groundwater flow model [24], land surface process model [18], transient numerical model [25], global climate models [26], regional climate models [15], etc. The second approach is using a regression model to fit the groundwater data to find the law of spatial and temporal changes of groundwater [13; 14]. Some researchers took a different approach and used qualitative sensing inversion methods to study groundwater characteristics qualitatively [27]; [PERSON] and [PERSON] used the Kruskal-Wallis test (K-W) for the spatial analysis of the concentrations of selected ions in groundwater.