The influence of water conveyances on restoration of vegetation to the lower reaches of Tarim River

Because of long-term stream-flow cut off in the lower reaches of Tarim River, environmental degradation has become the most severe and widespread environmental problem in Tarim River basin. Nine ecological water conveyances to the lower reaches of Tarim River made ecological environment change a lot. 3S technology was used to monitor dynamic change of ecology. However, remote sensing area index cannot analyze ecological restoration degree of Tarim River precisely because the time of each water conveyance is short, the change of vegetation area is not obvious, and there exists visual interpretation error. In this paper, remote monitoring datum of high temporal resolution and high spatial resolution were used to research the relationships between normalized difference vegetation index (NDVI) and the groundwater depth, between NDVI and the surface vegetation coverage, and between the groundwater depth and the surface vegetation coverage. The growth and restoration of the vegetation in different periods were evaluated by investigative analysis of the change trend of NDVI. The conception of relative restoration degree was proposed and the response of vegetation restoration to the water conveyance was evaluated. The evaluation result suggests that: first, the response of vegetation to the water conveyance concentrates within 1,000 m of both riversides, and the range of influence becomes smaller along the lower reaches of Tarim River. Second, influenced by the groundwater recharge, the vegetation coverage shows decreasing trend with the increase of off-river distance. Third, the vegetation coverage shows decreasing trend along the watercourse influenced by the water consumption. Finally, in spatial, original scattered meadow of low coverage transforms to high coverage gradually in research region. Vegetation response to the water conveyance expands to both sides with the watercourse being the axis, and expanding scale increases continuously.