Abstract: To understand the eco-hydrological responses of the ecological water conveyance project (EWCP) in the Heihe River, we used long-term monitoring data and remote sensing data, and employed spatial analysis, trend analysis, regression analysis and structural equation modeling to identify the spatial and temporal variations in groundwater depth, surface water bodies and NDVI in Ejina oasis in the lower reaches of the Heihe River since the implementation of the EWCP (2000-2020). The responses of oasis hydro-ecological indicators to the EWCP were analyzed, and the structure and strength of the drivers of vegetation restoration were clarified. The results showed that during the last two decades, the average annual runoff at Langxinshan hydrological station (LXS) showed a significant increase trend with 2.7×10⁷ m³. The groundwater level raised by 0.41 m on average. The area of the surface waterbody increased by 130.62 km². The NDVI showed a significant increasing trend, with the increased region occupying 42.34% of the total area. The middle reaches of the West River and the lower reaches of the East River dominated the rise of the NDVI. The response of NDVI to runoff was more sensitive in the West River area than that in the East River area. The vegetation area and NDVI remained relatively high level when the runoff in LXS was over 6×10⁸ m³ and the mean groundwater depth was lower than 2.8 m. Runoff, groundwater depth, and farmland area had different degrees of direct and indirect effects on oasis vegetation. The guarantee of runoff and the stability of groundwater in the lower reaches of Heihe River are the key drivers for the restoration and sustainable development of Ejina oasis.

Key words: ecological water conveyance, groundwater, surface water, oasis vegetation, restoration.