The Drought that Can’t be Seen

Australia: The Land Where Time Began

A drought of crisis proportions is affecting the Western Hemisphere. Crops are failing in Central America with millions being in danger of starving, and according to McNutt if the drought doesn’t break soon, ships passing through the Panama Canal will need to lighten their loads, which would increase prices for goods transported globally. The drought-stricken region spans a vast area in the western United States that is responsible for much of the fruit, vegetables, and beef that is produced by the US. Water users have turned to tapping groundwater aquifers as the drought has worsened to make up the deficit for people, crops, livestock and industry. According to McNutt, re-greening the landscape and filling the streams, lakes and reservoirs the aquifers will remain severely depleted even when rain does return. It is this drought, the underground drought that can’t be see, that is enduring and worrying, and in need of attention.

A global look at the depletion of underground water has been provided by the Gravity Recovery and climate experiment (GRACE) satellites, by monitoring small temporal changes in the gravity field of the Earth. It was confirmed by GRACE that there has been massive losses from the aquifer that lies beneath the agriculturally important Central Valley since the 1980s.

See California's Central Valley Groundwater Study: A Powerful New Tool to Assess Water Resources in California's Central Valley

In the decade between 2003 and 2012, the drawdown was equivalent to the entire storage volume of Lake Mead, which is the largest surface reservoir in the US. Wells have run dry which leads to detectable uplift or rebound of the land due to the displacement of water (see Borsa et al., p. 1587).

A natural long-term solution to water storage is underground reservoirs. The expense and environmental issues associated with the building of dams is avoided by taking advantage of aquifers. Aquifers are not subject to evaporative loss, which differs from the situation of surface aquifers, though they are recharged only slowly under natural conditions as excess precipitation percolates into the aquifer. The average age of groundwater, in some cases, can be many thousands of years old, dating back to times of wetter climates. Though at times, when water is withdrawn at prodigious rates, hydrological processes are not able to recharge the reservoirs fully, especially where the surface of the ground is built over with impervious surfaces.

E.g., in the Tucson area, water from the Colorado River is used to recharge artificially the aquifers with excess water in wet years that can be tapped later in dry years. It is guaranteed by the statewide 1980 Groundwater Management Act that over a 10-year period the aquifer cannot be overdrawn. The California legislature, the last state in the west that doesn’t have groundwater regulation, has been prompted by the current crisis, to pass a series of bills establishing state-level oversight of pumping from aquifers.

Surface water and groundwater are all part of a single coupled system, and they respond on different time scales to precipitation changes.

Sources & Further reading