Paper Reviewed
Gorelick, S.M. and Zheng, C. 2015. Global change and the groundwater management challenge. Water Resources Research 51: 3031-3051.

Back at the turn of the century, Wallace (2000) wrote that the projected increase in the number of people who will join our ranks in the coming half-century (a median best-guess of 3.7 billion) is more sure of occurring than is any other environmental change currently underway or looming on the horizon. And, it is quite clear, these extra people will need a whopping amount of extra food, which will take an equally whopping amount of extra water to produce, the only problem being that there is no extra water.

"Over the entire globe," Wallace further stated that "a staggering 67% of the future population of the world may experience some water stress," which translates into food insufficiency; and food insufficiency means malnutrition and, in the most extreme cases, it can mean starvation and war.

So what's the solution? There's really only one answer: we must produce much more food per unit of available water, which leads to the most important question of all. How can it be done?

In a paper published seven years later in the Philosophical Transactions of the Royal Society, Morison et al. (2007) wrote that (1) "agriculture accounts for 80-90% of all freshwater used by humans," that (2) "most of that is in crop production," and that (3) "in many areas, this water use is unsustainable." In fact, even at the time of their writing (nearly a decade ago), they noted that farmers in many countries were (4) "faced with legislative restrictions on use of water," which restrictions have subsequently become even more numerous and severe.

Fast forwarding to the present, Gorelick and Zheng (2015) write that "groundwater represents the largest stock of accessible freshwater and accounts for about one-third of freshwater withdrawals globally," citing Siebert et al. (2010) and Famiglietti (2014), while adding that "the hydrologic science and water management communities are not keeping pace with what is necessary to halt and resolve systemic long-term effects of depletion and degradation of groundwater resources," which further means that continuing groundwater overexploitation is unsustainable. So what can be done to improve this sad situation?

The answer is as simple as not interfering with the historical and still-ongoing increase in the atmosphere's CO2 concentration, since this latter phenomenon dramatically increases the water use efficiencies of essentially all agricultural crops -- see Water Use Efficiency (Agricultural Species) in our Subject Index -- thereby enabling farmers to produce ever-increasing quantities of the vast array of grains, fruits and vegetables, as well as animal feed crops, upon which the inhabitants of all nations of the earth ultimately depend for their sustenance, all of which can be accomplished without the need to extract ever greater quantities of ever-more-difficult-to-obtain water from earth's soils.

References
Famiglietti, J.S. 2014. The global groundwater crisis. Nature Climate Change 4: 945-948.

Morison, J.I.L., Baker, N.R., Mullineaux, P.M. and Davies, W.J. 2007. Improving water use in crop production. Philosophical Transactions of the Royal Society B 363: 639-658.

Siebert, S., Burke, J., Faures, J.M., Frenken, K., Hoogeveen, J., Doll, P. and Portmann, F.T. 2010.Groundwater use for irrigation: A global inventory. Hydrology and Earth System Sciences 14: 1863-1880.

Wallace, J.S. 2000. Increasing agricultural water use efficiency to meet future food production. production. Agriculture, Ecosystems & Environment 82: 105-119.