Presenters
Bridget R. Scanlon, PhD
Ashraf Rateb, PhD
Bureau of Economic Geology, The University of Texas at Austin
Abstract
Understanding the relative importance of climate extremes (droughts and floods) and human water use is critical for sustainable water management. GRACE satellites provide an unprecedented opportunity to track changes in terrestrial total water storage to compare with climate forcing and human water use. Here we show that climate is the dominant driver of total water storage changes in the 14 major U.S. aquifers over the past 15 yrs. (2002–2017) but human water use amplifies or dampens these changes. Effects of long-term droughts in the Central Valley and southern High Plains are amplified by groundwater pumpage, resulting in unsustainable depletion of -30 to -40 km3 over 15 yr. Lower drought intensities in the northwest and north central aquifers are partially dampened by surface water irrigation with up to 22 km3 water storage increase in the Northern High Plains. Although the Mississippi Embayment Aquifer is subjected to intensive groundwater irrigation, the GRACE satellites suggest minimal water storage depletion which suggests that irrigation is capturing stream water rather than depleting groundwater in the shallow alluvial aquifer. These GRACE results contradict previous monitoring and regional modeling output that suggest widespread groundwater depletion in the Mississippi Embayment aquifer. Long-term, decadal regional modeling results in the southwest and northwest are consistent with the recent satellite data showing groundwater storage decreases in the southwest and increases in the northwest. Approaches towards more sustainable water management include conjunctive use of surface water and groundwater within the context of floods and droughts. Inefficient surface water irrigation and efficient groundwater irrigation should be optimal from a groundwater storage perspective. Excess surface water from flooding could be captured and stored in depleted aquifers that are a legacy of previous overexploitation to promote more sustainable water resources management in the future.
