The Nature Conservancy logo. Protecting nature. Preserving life.A report released July 20 by the Natural Resources Defense Council and which I coauthored shows that climate change is projected to increase risks to water supplies in many parts of the United States:

  • Nearly one-third of all U.S. counties will experience high or extreme risk to their water supply sustainability by 2050, three times the number of counties that would be at risk without climate change (see figure below).
  • And more than 70 percent of all counties will have at least moderate risk to their water sustainability.
The report — written by a joint research team from Tetra Tech, Santa Clara University and The Nature Conservancy — calculated water-supply sustainability risk based on five criteria: 1) use of renewable water; 2) sustainable groundwater use; 3) susceptibility to drought; 4) growth in water demand; and 5) future increased need for water storage.

Climate change chart

Figure 1: Water Supply Sustainability Index indicating risk in 2050, without climate change (assuming historic conditions), and with climate change (A1B future emissions scenario).  The risks are classified into four categories based on the water sustainability criteria described above: Extreme (meeting > 4 criteria); High (3 criteria); Moderate (2 criteria); and Low (0-1 criteria).

This analysis shows that climate change will not just impact people in other parts of the world who are living in poverty, but will impact people, ecosystems, and businesses in the United States.

We cannot wait to address these problems when they arise in the future, but we need to take two steps: 1) act now to slow climate change, and 2) start preparing on the ground in specific places to cope with and adapt to the projected impacts.

A few places on the future water sustainability map really jump out as being at risk. One of the most striking is the area of the High Plains from Nebraska to Texas that covers the Ogallala Aquifer — one of the largest aquifers in the world and historically critical to people and agriculture in the High Plains region.

About 30 percent of water used for farmland irrigation in the U.S. comes from the Ogallala Aquifer. Unfortunately, the aquifer recharges at a very slow rate compared to the rate of water extraction. Water levels in the Ogallala have dropped by estimates of more than 100 feet in many places since water extraction began through 2005 (see map). Some estimates say the aquifer could dry up in as few as 25 years.

Aquifer chart

Figure 2: Water-level declines in the Ogallala Aquifer through 2005.

But we can respond with on-the-ground actions to help moderate the impacts and slow the decline of this aquifer. One example is the U.S. Department of Agriculture’s Conservation Reserve Program, which pays farmers to restore agricultural land to natural habitat, reducing water use and increasing water infiltration into the aquifer.

Florida is another area that is already experiencing extreme water sustainability risk, and it will worsen under climate change. But on-the-ground actions are already being taken in Florida through the restoration of wetlands, preserving the ability to store water naturally in the landscape.

The USDA’s Natural Resources Conservation Service (NRCS) — in partnership with The Nature Conservancy and landowners — is implementing an $85 million Wetland Reserve Program project in the northern Everglades, the largest such project in the program’s history, to restore wetlands and protect habitat, re-establishing the natural hydrology and providing tens of thousands of acre-feet of “dispersed water storage” on over 30,000 acres of ranchlands.

Partnering with Disney, the Conservancy pioneered this approach in the 1990s and 2000s at its 12,000-acre Disney Wilderness Preserve in central Florida and later on privately owned working ranches. Another model of “dispersed water storage” is being implemented by the World Wildlife Fund’s Florida Ranchlands Environmental Services Project, which pays ranchers to improve water storage and enhance wetlands on their land.

Through the restoration of large and small wetlands throughout Florida, water will move more slowly through the region as it did historically, providing greater flexibility of use for nature and people.

All in all, this report sends a strong and clear message that climate change will negatively impact water supply sustainability in the U.S. And these projections assume that we wil reduce our carbon emissions levels starting now. If we do not enact climate policy soon, these future projected impacts will be even worse.

Some elements of a strong U.S. climate policy would include:

  • Emissions of carbon dioxide and other heat-trapping “greenhouse” gases are causing climate change. We need to significantly reduce greenhouse gas emissions from all major emitting countries, industries and sources.
But even with the strongest climate policy, there will be increased risk to water supply sustainability in the United States. So we need to start preparing for the changes to come.

Ecosystem-based adaptation approaches such as the above examples in Texas and Florida are available to help protect our natural resources while providing the people protection against climate change impacts to water supplies. You can learn more about how the Conservancy is helping people and nature adapt to climate change — and how your help is essential to furthering that work.

— Text by Evan GirvetzCool Green Science Blog

Climate change: Risks to U.S. water supplies will increase
A new report projects that climate change will endanger water supplies across much of the United States -- but there's still time to prevent the worst, says Con