Relative Impacts of Climate Extremes and Irrigation Water Use on Water Storage in Major Aquifers based on GRACE Satellite Data

Abstract:

Understanding the relative importance of climate extremes (droughts and floods) and human water use (particularly irrigation) on water storage is important for sustainable management of water resources. The objective of this analysis was to evaluate linkages between climate forcing and water use on spatiotemporal variability in total water storage changes, tracked by GRACE satellites over 15 yr (2002 – 2017) in the 14 largest U.S. aquifers. Results show that in the California Central Valley and Central/Southern High Plains aquifers, total water storage was depleted by drought and amplified by groundwater-fed irrigation, totaling ~70 km³ (2002–2017), ~2× Lake Mead capacity. In the Pacific Northwest and Northern High Plains aquifers, lower drought intensities were partially dampened by surface-water irrigation and managed aquifer recharge, increasing total water storage by up to ~22 km³. In the Mississippi Embayment aquifer where irrigation applications are similar to or 50% greater than those in the southern Central Valley, GRACE data suggest negligible total water storage depletion over the 15 yr period whereas the regional model suggests depletion of ~120 km³ over this time. Negligible depletion may be related to most irrigation pumpage, primarily derived from groundwater (~85%), capturing surface water rather than depleting storage because 90% of the pumpage is in the Mississippi River Valley Alluvium aquifer that is closely connected with streams. In addition, inefficient flood irrigation (~80% of irrigation systems) readily recharges groundwater. GRACE data show that water storage changes in major aquifers are driven mostly by climate extremes and are amplified or dampened by irrigation applications.GRACE satellite data have critical implications for many nationally important aquifers, highlighting the importance of conjunctively using surface-water and groundwater and managed aquifer recharge to enhance sustainable water resource development.