Long-term regional groundwater responses and their ecological impacts under agricultural water saving in an arid irrigation district, upper Yellow River basin

Under long-term agricultural water saving strategy implemented in the Yellow River basin (YRB), this study analyzed long-term regional groundwater responses and their ecological impacts in an arid irrigation district (Hetao) in the upper YRB. The Mann-Kendall trend test was adopted to examine the trends of the monitoring data of climatic-anthropogenic factors and groundwater depth-salinity, as well as the modeling and remote-sensing results of natural vegetation growth. Results indicated significant decreasing net water diversion while increasing drainage since agricultural water saving, which is a major cause of groundwater reduction instead of climatic factors. This reduction was further confirmed with significant increasing groundwater depth (GWD) trends found in about 90 out of the total 224 monitoring wells across Hetao during 1970–2015. An overall salt accumulation was recognized for Hetao, but groundwater salinity only significantly changed in a few areas with insignificant trends found for more than 70 out of the total 114 monitoring wells during 1995–2015. Meanwhile, significant large-scale decreasing trends were detected for both simulated natural vegetation biomass and remote-sensing derived vegetation index, and wetland loss problem was also found. Particularly, relatively strong similarities were found among the spatial distributions of significant increasing GWD, decreasing vegetation biomass and index, and losing wetlands. This further suggested that the reduction might have caused negative ecological impacts. Overall, the results provided important information regarding long-term regional groundwater responses and their ecological impacts under agricultural water saving, which is significant for agricultural water management for arid irrigation districts.