Response of vegetation evolution characteristics to ecological water transport in the lower reaches of Tarim River in recent 20 years

After the implementation of ecological water delivery in the lower reaches of the Tarim River, the ecological environment initially improved. To evaluate the response of vegetation to the amount of ecological water delivery and groundwater level after ecological water transfer, this study used plants from the lower reaches of the Tarim River as the research object, using nearly 20 older time series of vegetation net primary productivity (NPP), normalized difference vegetation index (NDVI), evapotranspiration (ET), and Simpson index of species diversity. The effect of ecological water transport projects on the growth of downstream vegetation was analyzed, and correlation analysis was used to reveal the correlation between the amount of ecological water transport and NPP, NDVI, ET, and species diversity. The results showed that:1) correlation analysis showed a significant positive correlation between ecological water delivery and NPP and NDVI, and ecological water transport mainly promotes vegetation restoration by affecting NPP and NDVI. 2) Under the interference of human factors in arid areas, ecological water conveyance has become an effective measure to raise groundwater levels. The overall uplift of groundwater is greater than 1.38 m, and the uplift increases with an increase in water transport. 3) Ecological water conveyance promotes vegetation restoration. The ecological water conveyance increased the downstream vegetation area, NPP, and ET, and the vegetation species diversity gradually stabilized. The vegetation area expanded significantly. After 2011, the vegetation production capacity tended to increase, the Simpson index of vegetation species diversity increased as a whole, and the species structure tended to be stable. This shows that vegetation growth in the lower reaches of the Tarim River has improved. Therefore, natural vegetation coverage increased, and vegetation growth improved after ecological water conveyance. The results of this study can provide a scientific reference for vegetation restoration in the lower reaches of the Tarim River.