Modeling the effects of improved irrigation methods in a groundwater system : a case study from the Amu Darya Delta, Uzbekistan

Suitable groundwater levels have a significant influence on vegetation growth, regional salinization, and ecological sustainability. Because of long-term low-efficiency irrigation methods and water canals, the stream flows vanish before reaching the South Aral Sea, leading to a rapid shrinkage of lake coverage since 1960. Meanwhile, the groundwater table in agricultural zones has continued to grow and recharge the Aral Sea, leading to increased salinization. Using a joint application of observation, remote sensing, and reanalysis data, a groundwater model was established to represent the historical aquifer condition and the efficiency of four possible management scenarios: drip irrigation under plastic mulch (Drip scenario), surface water-groundwater conjunctive irrigation (Conjunction scenario), drainage system methods (Drainage scenario), and mixing of the aforementioned methods (Mixed scenario). The simulation results demonstrate distinct spatial distribution of groundwater tables: the decline in the groundwater level was discovered in all proposed methods, but the decline was more drastic in the Conjunction and Mixed scenarios, and least in the Drainage scenario. The decrease in the groundwater table can be attributed to the decrease in the recharge rate (Drip and Conjunction scenarios) and the increase in the pumping rate (Conjunction scenario). Of all the scenarios, the Drainage scenario shows the smallest global decline in the water table, with an average decline of 0.15 m, but a maximum regional decline of 3.93 m (on the sides of the drainage). Evaluated by analyzing the water balance at a regional scale, evapo-transpiration (ET) is still the major consumer of groundwater resources, at approximately 52%. Groundwater extraction and leakage into drainage accounted for approximately 6.9% and 23.5%, respectively. However, improved irrigation measures could reduce surface runoff and convert excessive groundwater into drainage systems. The improved irrigation methods could increase the total surface water runoff to 19.16 km3/yr, which is 29% higher than the maximum annual runoff (14.82 km3) and 406% higher than the mean annual runoff (3.79 km3) of the Amu Darya River over the past two decades. This study indicates that proper groundwater man-agement measurements in irrigation areas could greatly help address water scarcity problems and promote sustainability in these ecosystems.