A new report by the consulting firm Tetra Tech reveals the impact climate change will have on water supply reliability in the United States and clearly demonstrates that urgent action is needed to move California toward more sustainable water supplies.

As part of its analysis, Tetra Tech used an index to assess risks to water supply reliability on a county-by-county basis. Fully one-third of all counties in the lower 48 states will face high risks of water shortage by 2050, and nearly half of those will face extremely high risks of water shortage. Water use in some of these high-risk areas like the Great Plains and the Southwest is already unsustainable. As climate change affects temperature and precipitation levels, the number of counties facing high water shortage risks will increase, and areas like the Great Plains and the Southwest may not have any available precipitation at all.

Higher temperatures mean less water for two principle reasons. First, a changing climate means shifts in precipitation, including a change in how much, where, and when rain falls. In California, we are likely to see more rain and less snow, for example. Second, warmer temperatures cause an increase in evaporation both from ground surfaces like lakes and reservoirs and through vegetation.

In the report Tetra Tech took into account an increase in water demand over the coming decades, estimating that total water demand in the United States may grow as much as 12.3% by 2050.

Tetra Tech’s analysis shows that climate change will have a significant effect on future water supplies, particularly in places like California that already contends with shortages. The report demonstrates why California must adopt the innovative new policies outlined in PCL’s 8 Affordable Water Solutions for California report, which include among others increasing water recycling and reducing water demand from new homes.  Tetra Tech’s full report is available here.