Unexpected groundwater recovery with decreasing agricultural irrigation in the Yellow River Basin

Groundwater is an important water resource for agricultural irrigation and industrial and domestic uses around the world, especially in arid regions. China's Yellow River Basin (YRB) is a typical arid and semiarid area where agricultural irrigation depends greatly on groundwater storage. In the YRB, a few ecological restoration projects, such as the Gain for Green project, reduced crop land over 6% around the year 2000, consequently leading to a decline in the groundwater withdraw for irrigation. A few studies emphasized the impact of land use and land cover change on evapotranspiration, soil moisture, and surface runoff processes; however, little is known about the groundwater recovery at the basin scale. In this study, we utilized multiple data sets, including satellite remote sensing (i.e., the Gravity Recovery and Climate Experiment, GRACE), ground observation, and simulation data from land surface modeling, to identify the trend in groundwater storage (GWS) and the roles of climate change and human activities during the period of 2005-2013. The results indicate that there was a consistent estimate for the GWS changes using GRACE and ground observations at the basin scale, indicating a substantial decrease at a rate of about - 3 mm/yr. Agricultural irrigation accounted for 61.69% (6.15 mm/yr) of the total groundwater consumption, decreasing by 12.6% from 2005 to 2012. However, the groundwater consumption for industrial, domestic, and public sectors increased, and total groundwater consumption was maintained a stable level of about 10 mm/yr. Therefore, groundwater storage did not recover despite the increased groundwater recharge and the decreased groundwater irrigation. To ease groundwater depletion, groundwater management should be concerned with water allocation for agricultural irrigation and also with industrial and domestic uses, emphasizing water saving and recycling techniques.