Charting Pathways Toward Sustainability for Aquifers Supporting Irrigated Agriculture

The question of how much longer groundwater can support large-scale agricultural production is one of global significance. Many of the world's regional aquifers supporting irrigated agriculture are on a trajectory toward resource depletion. In the absence of alternative water supplies, the only viable near-term (few to several decades) option for redirecting these heavily stressed systems on to more sustainable paths is to reduce pumping. The key issues therefore become how much should pumping be reduced to significantly extend an aquifer's lifetime and what is the likelihood of attaining a sustainable condition. We have developed a water-balance approach to glean insights into these issues and chart pathways toward more sustainable states. An aquifer's response to pumping reductions heavily depends on the net inflow component of an aquifer's water budget, both in terms of its magnitude and how it decreases with time in response to reductions. If a reduction leads to a pumping rate that is above net inflow, the aquifer lifespan can often be extended by a factor of two or more, but depletion will be the final outcome. In contrast, if a reduction results in a pumping rate more than 10% below net inflow, a lengthy period of apparent sustainability will result. In that case, the aquifer lifespan may be extended long enough so that other options, such as large-scale water transfers or development of more sustainable crop mixes, become viable. These concepts are demonstrated using examples based on an ongoing experiment in pumping reductions in the High Plains aquifer.