## 4 Discussion  
By studying the trend of drought change in MUSL from 2001 to 2020, it was found that the western part was mainly dominated by an increasing trend (mainly distributed in Oto Front Banner), and the eastern part of the TVDI was dominated by a decreasing rate. These findings were consistent with the findings of [22] yet differed from those of [PERSON] et al. [10]. On the one hand, it is difficult to determine the precise level of drought at broad scales or in areas with few meteorological stations due to the difficulty of calculating the SPEI index for studying droughts using data from a limited number of meteorological stations. On the other hand, this is due to the utilization of various drought assessment parameters as a foundation for classifying the identical metric into drought grades, the duration length of the investigation, and division boundaries. These factors can lead to contradictory conclusions. Figure 14: (**a**) Maximum partial correlation coefficient and (**b**) lag times of TVDI with precipitation, temperature, and ET for different land use types. Over the previous 20 years, a highly significant drying trend has dominated the MUSL TVDI. However, in the next time frame, the severity of the drought in Shenmu City, Shaanxi province, and central Ordos diminished, especially in summer, when 72.13% of the area will change from dry to wet. This occurrence will mostly be owing to the MUSL program that converted farms back to forests while grasslands and the warmer and wetter climate have increased vegetation cover to alleviate drought [34]. Moreover, the climate of the continually drying zone through the southern portion of MUSL is mostly cropland, with high altitudes and specific salts in the parent material of the soil, all of which have a severe negative influence on a boost of plants [35], and 58.7% of the plants in MUSL \"turned green\" as a result of the rise in CO\({}_{2}\), which led to an increase in NPP, an increase in ET [36], a decrease in soil moisture, and an intensification of drought [37]. The most severe droughs occur in the spring, when temperatures rise quickly, and precipitation levels drop as a result of shifting monsoon patterns [38; 39] and the notable rise in the number of days with high temperatures [40]; further, the investigation's results demonstrate an excellent relationship between the multi-year TVDI allocation features and the geographic distribution of annual mean precipitation; Moreover, El Nino-Southern Oscillation (ENSO) and drought are closely linked [41], and the El Nino phenomenon is thought to possess a bigger influence on dryness throughout MUSL. [10]. Vegetation restoration from 2001 to 2010 increased ET by 51 mm in MUSL [42], which can then cause the soil to dry up and prevent vegetation development, particularly in grasslands, resulting in a longer-lasting drought. Having pointed out that dryness affects plants with a time lag [43], globally, drought usually has a lag time of one month for 88.37% of grasslands [44]. Currently, grassland makes up 58.71% of the MUSL due to vegetation restoration; however, on the investigated dimension, vegetation reacts to climate variability 1-2 months later than it does in adjacent regions [45]. Thus, while drought has an indirect lag effect on climate, does drought also have a direct lag effect on the weather elements? Therefore, to seek ways to enhance our comprehension of climate variability and the dynamics of drought feedback, this paper explores, in detail, the lagged relationship of TVDI on precipitation, temperature, and ET for different land use types at different scales. The results of this paper show that annual scale TVDI responds more quickly to precipitation than ET and temperature because the effects of temperature and ET on drought need to accumulate over a period of time to have a large impact on the current drought.