Evolution characteristics of groundwater and its response to climate and land-cover changes in the oasis of dried-up river in Tarim Basin

Abstract

Groundwater is essential for agricultural, ecological and domestic water use, and its depletion under climatic and anthropogenic impacts can impose challenges on regional water resources and ecological security, particularly in arid regions. Spatiotemporal variation and drivers of groundwater are critical to understand groundwater cycling and restore groundwater, while they are poorly understood in arid oasis region due to sparse field monitoring. To address this, we examined the spatiotemporal variations and controlling factors of groundwater level and mineralization degree using data collected at 22 wells in the Wei-Ku Oasis of Tarim Basin during 2000–2018, a typical arid inland river basin in northwest China. Results showed that obviously large spatial and temporal variations existed in both DGL (depth to groundwater level) and DM (degree of mineralization). Groundwater level was the shallowest in spring and deepest in autumn. DGL exhibited a markedly increasing trend (2.05 m per decade), while DM marginally decreased (-0.21 g/L per decade) (p < 0.001) during 2000–2018. The spatial distributions of DGL and DM were complex. Larger variation of DGL/DM generally occurred at the areas with greater DGL/DM. DM in the northwestern part was obviously smaller than that in the southeastern part. The variation of DGL in the eastern region was noticeably larger than that in the western region. Human activity was the main driving factor of DGL increasing, climate change had a dominant role in DM decreasing, and the relationship between controlling factors and groundwater varied in space and season. Decreasing riverbank leakage and increasing volume of evapotranspiration, groundwater pumping and water drainage led to decreasing groundwater level, while increasing infiltration/leakage from irrigated water, canal and reservoir resulted in increasing groundwater level. The results could help to advance the understanding of groundwater cycling mechanism, and be useful in improving sustainable groundwater management and restoring ecosystem in arid region.