Integrated modeling to assess the impact of climate change on the groundwater and surface water in the South Aral Sea area

Abstract

The recession of the South Aral Sea over the last few decades has become a great environmental challenge in Central Asia. Due to declining inflow and irrigation exhaustion, the Amu Darya River vanishes before reaching the South Aral Sea. Therefore, groundwater (GW) has become the vital water source for the South Aral Sea surface water and the local ecosystem. To develop feasible adaptation strategies for water resource management, it is necessary to quantify the GW flux into the South Aral Sea under ongoing climate change. Based on numerical models (MODFLOW and SWAT) and with the support of observed data, remote sensing data, reanalysis data, and the output of Global Circulation Models (GCMs) of the Coupled Model Intercomparison Project Phase 6 (CMIP6), the hydraulic connection between a shallow aquifer and the lake was investigated and projected for future change. The GW model was calibrated by one in-situ GW well and six Gravity Recovery and Climate Experiment (GRACE) derived GW heads. The root mean square error (RMSE) of the GW flow field simulation (MODFLOW) was lower than 0.21 m from 2005 to 2016. Under three shared socioeconomic pathways (sustainable pathway, medium pathway, and fossil-fueled development), the GCMs indicate that the evapotranspiration (ET) experiences the greatest change, and will potentially rise to 602.6 mm/yr by 2100 in fossil-fueled development. While the precipitation and the runoff of the Amu Darya River will both rise slightly, and with the range of 146.4–163.3 mm/yr and 107.8–118.4 m3/s from 2021 to 2100 separately, and the increase is mainly during winter. With climate change signals forcing on the historical hydrometeorological data, the simulation result revealed that the GW contributes to more than 78 % of the total influx of water into the lake during 2021–2100, and the predicted GW flux into the lake will slightly rise over time. However, the ET will also increase due to rising temperatures and may gradually outpace the recharge growth. The simulation results indicate that the South Aral Sea may maintain a surface area of 4.47×103km2 in fossil-fueled development, which means it will continue to shrink if there is no human intervention. Therefore, a set of sustainable water resource management methods is urgently needed to preserve the ecological environment of the South Aral Sea and prevent ecological disasters.