## 3 Results
### Spatial Distribution of Groundwater Depth  
Compared with a single groundwater depth as an interpolation factor, the cokriging interpolation makes the result smoother in space, and has no abrupt point-like aggregation characteristics, which can better reflect the spatial distribution of groundwater (Figures 5 and 6). The results are more obvious in spatial differentiation. Among them, the difference in groundwater depth in the study area is obvious, and the depth of groundwater is greatly affected by land-use type. In the four years, the groundwater depth on the east side is relatively large, mainly distributed in the farmland centered on Shengli Village in the lower reaches of the Xilamulun River and the dune wasteland near Dale Benji. The central and eastern parts of Wengniute Banner are mainly plain dunes, covered with vegetation such as wild grasses. Years of drought and lack of water have resulted in lower groundwater depths within this range. Although large areas of farmland are adjacent to the Xilamulun River and there is a certain amount of crop cover, the water demand is also huge due to intensive crop planting. Residents generally dig wells around the farmland to irrigate the land nearby. The amount of water causes the groundwater depth in large-scale farmland to be generally deeper. The farmland concentration area in the lower reaches of the Laoha River is similar. The area with better groundwater depth is mainly distributed in the west. According to the results of four years' interpolation, the vegetation coverage in the western mountainous areas is relatively high, and there are many tall and dense shrubs. The diversity of plants with improved, developed root systems and good soil environment are all conducive to the maintenance of soil moisture. A large amount of water could be fixed in the soil by the rainfall; therefore, the groundwater depth is generally shallow in the eastern part of the study area. The severely water-deficient areas in Wengniute Banner are mainly low-mountain hills, loess hills, and loess terraces, and their geology, geomorphology, and hydrogeological conditions are extremely complex. By analyzing the geological and hydrogeological environment of groundwater in the study area, the water quantity is abundant and the water quality is good, which can meet the needs of human and animal life, industry, agriculture, and animal husbandry in the area; however, water shortages are more serious in low hills, loess hills, and loess plateau areas. Factors such as precipitation, topography, lithology, and groundwater circulation are the main reasons for the serious water shortage in this area. Stratum lithology and neotectonic movement are the decisive factors affecting the enrichment of groundwater. Comparing the groundwater depth interpolation results in 2005, 2009, 2013, and 2017, the variation law of groundwater depth in time was analyzed with four years as the boundary. In 2005, the groundwater depth was between 2.7 and 4.1 m, and the overall distribution was relatively uniform. The groundwater depth was mainly distributed in the dune area of the northeastern part of the study area, and the groundwater depth in most areas exceeded 3 m. It indicates that groundwater diversion and convergence are relatively smooth in the past year, and there are few obstacles in the transmission process. In 2009, the groundwater depth was between 2.7 and 4.3 m, and its situation was not significantly different. The area with large groundwater depth was concentrated in the northeast and southern farmland. It indicates that the groundwater depth this year was greatly affected by location coupled with low precipitation. The groundwater depth in the river area and the farmland area is relatively close, and the farmland needs excessive extraction of groundwater for agricultural irrigation. In 2013, the groundwater depth was between 2.9 and 4.5 m, and the difference was small.