Challenges and impacts of climate change and human activities on groundwater-dependent ecosystems in arid areas - A case study of the Nalenggele alluvial fan in NW China

摘要

Desert oases exist around the alluvial fans of inland river basins in arid areas, where the vegetation growth is wholly dependent on groundwater due to scanty rainfall and arid environment. Climate change and water resources exploitation may threaten the groundwater-dependent ecosystems (GDEs) in the arid areas; a case study was proposed to evaluate the vegetative growth state with the normalized difference vegetation index (NDVI), hydrometeorological data, and the exploitation of water resources of the Nalenggele alluvial fan in northwest China. Climate change, and increasing temperature and precipitation may be indispensable factors for vegetation growth; however, based on the results of a correlation analysis, it was found that climatic factors shared little direct correlation with the NDVIs of the Nalenggele alluvial fan. Also, the depth to groundwater table (DWT) and distribution of shallow groundwater (DSG) are the direct influencing factors of vegetation growth. DWT and DSG are mainly controlled by the groundwater recharge mechanism and the original water sources from snowmelt, which are directly correlated with climate change. Predictions for DWT and DSG were made considering water resource exploitation and different river discharges amid climate change. The results reveal that the distribution area of shallow groundwater with the ecological water level (DWT < 4 m) in 2020 will decrease to approximately 78-86% of that in the status quo year, which suggests vegetation may be at risk of degradation from the combined influence of climate change and human activities. Therefore, management strategy and legislation for protecting GDEs should be proactively initiated in other similar areas in China.