The critical role of local policy effects in arid watershed groundwater resources sustainability: A case study in the Minqin oasis, China.

Designed as a watershed groundwater restoration policy (WGRP), the Comprehensive Treatment Program of the Shiyang River Basin (CTSRB) was launched in 2006 to restore the groundwater resources in the Minqin oasis, northwestern China. This study sought to verify the recovery effects of CTSRB implementation from the perspective of groundwater depth. We reconstructed the spatio-temporal distribution of groundwater depth at interannual and pixel scales by using digital groundwater depth models (DGDMs), based on the ordinary kriging interpolation method. Using DGDMs data, various measures of the groundwater table (e.g., regional depths, surface areas, depletion cones, and conditions in irrigated regions including Ba, Quanshan, and Hu) were quantitatively analyzed and compared for the pre-CTSRB (2001-2006), CTSRB I (2006-2010), and CTSRB II (2010-2015) periods, for which spatial trends in the annual amplitudes of groundwater depth were compared. Finally, strategies that impacted the groundwater behavior before and during the CTSRB periods, possible indirect and adverse effects, and long-term strategies and prospects were discussed. The results showed that groundwater depth first declined sharply, before increasing slowly and stabilizing after implementation of the CTSRB. Areas of greater groundwater depth (<-20m) and four groundwater depletion cones expanded during the pre-CTSRB period, whereas variable shrinking trends were detected during the CTSRB period. Spatial analysis showed that groundwater recovery mainly occurred along the periphery of the three irrigated regions, among which recovery effects in Hu were more obvious than those in Quanshan and Ba, with pumping-well densities the main reason for the difference. Therefore, various strategies (increasing the surface water supply, reducing groundwater mining, and some other auxiliary measures) of CTSRB together supported groundwater recovery in the Minqin oasis. Overall, this research demonstrates an innovative perspective to verify the effects of WGRPs in arid and semi-arid areas.