Groundwater dynamic response mechanism and quantity vulnerability assessment under the influence of human activities.

Groundwater depletion becomes a prominent issue due to the fast-growing water demand in semiarid and arid regions, which poses serious hydrogeological problems and restrains regional sustainable development. Groundwater dynamic response mechanism analysis and quantity vulnerability assessment are useful methods for groundwater protection and management. This paper analyzed the spatial and temporal variation of groundwater level in Xi'an, and studied the response characteristic of groundwater dynamic to its driving forces in different periods under the influence of human activities. Considering both hydrological settings and human disturbances, a modified evaluation system based on fuzzy comprehensive evaluation method and DRYTECL model was proposed to assess groundwater quantity vulnerability. In order to make the results more reasonable and in line with actual situation of the study area, a weighting system that builds on subjective and objective weights was put forward as well. The results show that groundwater level sharply dropped in the last few decades, and the spatial autocorrelation of groundwater level has gotten weaker, suggesting that the contribution of natural factors to groundwater-level variation decreased. Land use, exploitation, and other human activities had a great influence on groundwater dynamic by changing the discharge and recharge condition of groundwater, and the response characteristic of groundwater level to precipitation, runoff, and exploitation varied with time and hydrogeological conditions. Groundwater quantity vulnerability map showed 63.8% of the study area fell within moderate-to-high quantity risk, which indicated that groundwater depletion mainly occurred in highly urbanized areas. The single-parameter sensitivity analysis showed that the exploitation is the most sensitive factor to groundwater quantity vulnerability, the real effects of land use on groundwater quantity risk are greater than its theoretical effects, and net recharge is important to groundwater recovery.