Groundwater depletion and sustainability of irrigation in the US High Plains and Central Valley

Abstract

Aquifer overexploitation could significantly impact crop production in the United States because 60% of irrigation relies on groundwater. Groundwater depletion in the irrigated High Plains and California Central Valley accounts for ~50% of groundwater depletion in the United States since 1900. A newly developed High Plains recharge map shows that high recharge in the northern High Plains results in sustainable pumpage, whereas lower recharge in the central and southern High Plains has resulted in focused depletion of 330 km(3) of fossil groundwater, mostly recharged during the past 13,000 y. Depletion is highly localized with about a third of depletion occurring in 4% of the High Plains land area. Extrapolation of the current depletion rate suggests that 35% of the southern High Plains will be unable to support irrigation within the next 30 y. Reducing irrigation withdrawals could extend the lifespan of the aquifer but would not result in sustainable management of this fossil groundwater. The Central Valley is a more dynamic, engineered system, with north/south diversions of surface water since the 1950s contributing to ~7× higher recharge. However, these diversions are regulated because of impacts on endangered species. A newly developed Central Valley Hydrologic Model shows that groundwater depletion since the 1960s, totaling 80 km(3), occurs mostly in the south (Tulare Basin) and primarily during droughts. Increasing water storage through artificial recharge of excess surface water in aquifers by up to 3 km(3) shows promise for coping with droughts and improving sustainability of groundwater resources in the Central Valley.

Fig. 1.

(A) Measured groundwater level changes from predevelopment (∼1950) to 2007 in the HP aquifer [modified from (7)]. (B) Simulated groundwater level changes from predevelopment (∼1860) to 1961 in the confined aquifer (17). Groundwater basins include the Sacramento, Delta/East sides, San Joaquin, and Tulare.

Fig. 2.

Trends in groundwater depletion in (A) the HP and (B) the CV aquifers. Depletion is concentrated in the southern regions of both basins, Texas in the HP and Tulare Basin in the CV. The HP data show generally monotonic declines based on water level monitoring in 3,600 wells (1950s) to 9,600 wells (2006) (7). Water level changes in the CV are much more dynamic with declines focused during droughts (1976–1977, 1987–1992, 1998–2003) and recovery at other times. D/E, Delta, Eastside; Sac, Sacramento; SJ, San Joaquin; TB, Tulare Basin.

Fig. 3.

Long-term mean annual recharge rates for the HP aquifer based on the chloride mass balance approach applied to groundwater chloride data. Recharge rates could not be estimated for the southern part of the SHP because groundwater chloride is impacted by upward movement of saline water from deeper aquifers.

Fig. 4.

Cumulative water storage in the Arvin Edison groundwater bank relative to precipitation. The data show declines in storage mostly restricted to droughts in 1976–1977, 1987–1992, and 1998–2003.