## 5 Discussion  
The vegetation NDVI of Ordos City has changed significantly in the past 21 years, and the increase in NDVI of vegetation in both interannual and seasonal seasons is inseparable from the national project of returning farmland to forest and grass. According to the relevant data, in recent years, the sand desertification land and desertification land area in Ordos City continued to decrease, and the control rates of Kubuqi Desert and Mu Us sand reached 25% and 70%, respectively. The Kubuqi Desert basically tends to be stable, and the sand damage in Mu Us sandy land basically disappeared. [PERSON] [34] analyzed the vegetation cover of the Loess Plateau in the past 30 years based on the LTDR NDVI and concluded that the change trend of vegetation NDVI was relatively larger in summer and autumn and the smallest in spring. This is basically similar to the conclusion of this paper, but there is a significant difference between the growth trend in summer and autumn, which may be related to the difference between the study area and the data set. in summer and autumn in Ordos City, the change of vegetation NDVI may be related to the implementation of rotational grazing in recent years and the local climate environment. In spring, because the vegetation has just entered the growth period, the NDVI value of the vegetation is low, so the growth trend is not obvious. The analysis of future trends shows that the vegetation NDVI in Ordos City will be mostly in a state of anti-continuous improvement in the future. This is basically similar to the conclusion of [PERSON] et al. [35] that the vegetation NDVI changes in the Loess Plateau from 2000 to 2016 show an increasing trend of anti-continuous improvement, which is mainly distributed in southwestern Inner Mongolia and other regions. Most of the land use in Ordos City is dominated by grassland. Although the growth trend of grassland has been improving in recent years, it is generally believed that the interference of factors is large; due to the poor ecological environment, grassland sensitivity is strong. In addition, Ordos City has vigorously developed forestry relying on the national Three-North Shelterbelt Project in recent years, but Ordos City is in the transition zone between semi-arid and drought, which is not suitable for large-scale implementation of forestry development. Taking the afforestation field in Ordos City as an example, the ratio of pure forest to mixed forest is 9:1. In the forest farm, Salix psammophila, Caragana korshinskii, and other shrub forests accounted for more than 60%. Most of the arbor forests are poplars, which have a simple stand structure, dilapidated forest phase, and low protection capacity. The path analysis between vegetation and climate factors showed that precipitation was the main factor, and an increase in precipitation basically promoted the growth of vegetation, while the increase in temperature inhibited the growth of vegetation in Ordos City. The effect of precipitation increase on vegetation growth is the response of water shortage climate conditions with extremely insufficient annual precipitation and very high potential evapotranspiration. An increase in temperature showed a negative effect on vegetation. In spring, vegetation was in the early growing season. With a small amount of precipitation and low temperature, there was a mutual negative interaction between precipitation and temperature. This had a negative indirect effect on vegetation growth. In summer, quick increases and high temperature showed negative effects on vegetation growth for the reason that high temperature enhanced the potential evapotranspiration and reduced soil water content. In autumn, an increase in temperature accelerated the wilting of vegetation in the late growing season. Research on the desertification of the Ordos Plateau showed similar results that the greening mainly depended on the increase in precipitation [36]. [PERSON] et al. also figured out that precipitation played a leading role compared with temperature [37]. [PERSON], et al.