Characterizing the Evolution of Groundwater Flow Field and Its Driving Forces in Xi’an, China

Abstract

This paper studied the temporal and spatial variation of groundwater levels that characterized the evolution of the groundwater flow field in Xi’an, China, from 1965 to 213, by using the wavelet analysis method. Then under the consideration of different hydrogeological conditions on a large scale, the hydrogeological areas were taken as research units, and the correlation between groundwater level and its driving forces were analyzed. Finally, the projection pursuit model (PPM) based on the particle swarm optimization (PSO) algorithm was adopted to identify the contributions of the driving forces in each hydrogeological unit. The results indicated that in the background of climate change and overexploitation in the last few decades, the groundwater level in Xi’an dropped sharply. There was a strong correlation between precipitation and groundwater level, especially in the flood seasons. In different hydrogeological areas, the sensitivities of groundwater level to precipitation were different. In addition, the groundwater level shows an exponential-function declining trend with the increasing exploitation, whereas in the groundwater sources, there was a negative linear correlation between groundwater level and exploitation. Likewise, the streamflow had an effect on the variation of groundwater level. The relative contributions of driving forces varied with the hydrogeological conditions. In conclusion, exploitation was the leading factor for the variation of the groundwater level, precipitation came second, and streamflow had an influence on groundwater levels in the regions adjacent to the rivers. The results indicated that in human-disturbed environments, hydrogeological conditions still play an important role in groundwater dynamic variation. Additionally, they suggested that the exploitation of groundwater should be adjusted to make it consistent with climate change; thus, the abnormal variation of groundwater flow field will be contained.