The Last Drop: Climate Change and the Southwest Water Crisis

The U.S. Southwest is currently relying on unsustainable groundwater extraction to meet water demands. Climate change is projected to exacerbate this crisis by increasing agricultural water needs and shifting snowmelt timing, leading to significant water shortfalls. The report finds that without adaptation, the region faces a cumulative water shortfall of up to 2,253 million acre feet over the next century under a severe climate scenario (A2). While desalination and imports are deemed non-viable due to cost and availability, planned reductions in urban and agricultural water use—particularly the elimination of low-value crops—could bring water use to sustainable levels. The economic cost of inaction is estimated between $2.3 trillion and $5 trillion over the next century.

• The U.S. Southwest is currently extracting groundwater at an unsustainable rate, and climate change will worsen this shortfall. Under the A2 climate scenario, the projected water shortfall for the region from 2010 to 2110 reaches 2,253 million acre feet.
• California serves as a primary example of unsustainable use, where groundwater demands over the next century are projected to be three times the available supply. Without adaptation, the state will face water shortfalls every year by 2050.
• Agriculture is the dominant water user in the Southwest, accounting for nearly four-fifths of the region's water, yet it contributes only 1 percent to the regional GDP.
• A significant portion of agricultural water is used for low-value crops, specifically hay, which accounts for 42 percent of the region's agricultural water. Eliminating the lowest value-per-unit-water crops (excluding hay) could reduce agricultural water use by 24 percent while reducing farm sales by less than 5 percent.
• Urban water use is projected to grow faster than agricultural use, with urban use expected to account for nearly one-third of total regional use by 2110. Nevada currently has the highest per capita domestic water use in the U.S. at 190 gallons per person per day.
• Increasing water supply through desalination or imports is not a viable long-term solution. Desalination is energy-intensive and expensive, with true costs for planned California plants estimated between $2,600 and $2,700 per acre foot.
• Planned reductions in water use are the only viable solution. 'Fast' adaptation in California—including significant conservation and price increases—is required to bring water use in line with renewable supplies.
• The economic cost of failing to act is immense. The baseline water shortfall over the next century is estimated to cost between $2.3 trillion and $4.0 trillion, with the A2 climate scenario potentially increasing this to $5 trillion.

APA

Ackerman, F., & Stanton, E. A. (2011). The Last Drop: Climate Change and the Southwest Water Crisis. Stockholm Environment Institute. https://www.sei.org/mediamanager/documents/Publications/Climate-mitigation-adaptation/Economics_of_climate_policy/sei-westernwater-0211.pdf

Chicago

Ackerman, Frank, and Elizabeth A. Stanton. The Last Drop: Climate Change and the Southwest Water Crisis. Stockholm Environment Institute, 2011. https://www.sei.org/mediamanager/documents/Publications/Climate-mitigation-adaptation/Economics_of_climate_policy/sei-westernwater-0211.pdf.

Wikipedia

{{cite report |last1=Ackerman |first1=Frank |last2=Stanton |first2=Elizabeth A. |title=The Last Drop: Climate Change and the Southwest Water Crisis |publisher=Stockholm Environment Institute |date=February 2011 |url=https://www.sei.org/mediamanager/documents/Publications/Climate-mitigation-adaptation/Economics_of_climate_policy/sei-westernwater-0211.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{ackerman2011last, author = {Ackerman, Frank and Stanton, Elizabeth A.}, title = {{The Last Drop: Climate Change and the Southwest Water Crisis}}, institution = {Stockholm Environment Institute}, year = {2011}, month = feb, url = {https://www.sei.org/mediamanager/documents/Publications/Climate-mitigation-adaptation/Economics_of_climate_policy/sei-westernwater-0211.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }