Water index (short of demand) 2050, United States…Credit: NRDC

In a study conducted by Tetra Tech, Inc. for the National Resources Defense Council (NRDC), a major U.S. conservation group, more than 1,100 counties in the United States will face water shortages by 2050. Over 400 counties will experience extreme water shortage conditions. These findings are based on the analysis of trends in growth of water use (especially population and energy demand) and the availability of renewable water supply given average results from sixteen established climate models. (These models reflect the conditions of a changing climate.) The study is not making predictions of where water shortages will occur, but given an unchanged usage pattern it does highlight those areas where water shortage is most likely to occur.

The Tetra Tech report develops a new water supply sustainability index. The risk to water sustainability is based on the following criteria: (1) projected water demand as a share of available precipitation; (2) groundwater use as a share of projected available precipitation; (3) susceptibility to drought; (4) projected increase in freshwater withdrawals; and (5) projected increase in summer water deficit.

[Source: NRDC]