Influence of natural and human drivers to groundwater storage changes

The bulk of freshwater resources available for human use are stored beneath the land surface as groundwater and are often tapped to sustain agriculture and domestic water use. Our ability to attribute natural and human drivers to changes in the availability, timing and volume of groundwater is difficult since these drivers occur concurrently. This work seeks to parse natural and human drivers to observed changes in groundwater storage due to a variety of factors using regression procedures and dominance analysis, given spatiotemporal changes in groundwater storage derived from remote sensing observations (Gravity Recovery and Climate Experiment (GRACE) satellites). The primary objective of this research is to exploit existing information in groundwater storage, climate factors and water use to quantify the influence of variables on the behavior of groundwater storage across the continental United States. Multivariate regression procedures and dominance analysis reveal that precipitation and groundwater recharge exert high influence in regard to the observed groundwater storage changes, while total annual groundwater withdrawals were found to exert relatively low influence. This result suggests that long-term groundwater pumping may have achieved a quasi-steady state dynamic as suggested by Theis. Further, the analysis suggests that short-term changes in groundwater storage may be more influenced by short-term weather phenomena, whereby short-term dry periods drive groundwater use resulting in rapid monthly changes in groundwater storage as observed from GRACE.