Changes in natural vegetation growth and groundwater depth and their relationship in the Minqin oasis in the Shiyang River Basin

The Minqin Basin is short of water resources and has a weak ecological environment. Understanding the relationship between groundwater table depth and growth of natural ecological vegetation is an important theoretical basis for precisely controlling groundwater exploitation and targeted protecting ecological environment. Previous studies lack correlation analyses, especially determination of ecological groundwater levels in the shallow buried area. In this study, we analyzes the spatial and temporal variation in the NDVI of the natural ecological vegetation and groundwater depth and the relationship, based on the LANDSAT remote sensing data and the measured data at 85 wells during 2000—2017.The results show that (1) NDVI was generally low in the study area, with the annual mean value of 0.1, and the value of NDVI became greater after 2012, reflecting the significant effect of the measurs of artificial afforestation and the like; (2) groundwater depth showed an increasing trend during 2000—2017, but the increase slowed down after 2008, and the groundwater table depth was greater than 20 m in the western part, but less than 20 m in the eastern and northern parts; (3) the groundwater depth suitable for vegetation growth is about 2.5~3.9 m, the NDVI is highly negative correlated with groundwater depth when the groundwater depth is less than 4 m, and the correlation coefficient between them was generally less than -0.8; (4) there was no obvious correlation between them when the groundwater depth was greater than 4 m. In this paper, the relationship between the growth state of natural vegetation and groundwater table depth in the Minqin oasis area was studied synthetically in the long time series and on the basin spatial scale, and the ecological groundwater level in the shallow buried area was obtained, and the key target area of ecological governance was preliminarily delineated.