The Last Drop: Climate Change and the Southwest Water Crisis

The Last Drop describes the current and projected future water-related challenges facing the Southwest region of the U.S. In particular, the present and future water demands of the agricultural and water sectors are examined, as well as how those demands will be affected by even minor changes in current climate variables.

This report offers an integrated picture of the effects of climate change on water supply, demand, and scarcity in the Southwest as a whole. Three new models of water and climate change are developed: a detailed depiction of California's supply and demand for water; a regional model of agricultural water use, and a regional model of water and electricity generation.

The report describes the ongoing Southwest water crisis and the ways in which it will be exacerbated by climate change. The authors note that adaptation measures, namely conservation and efficiency, can reduce regional water use and help prevent unplanned water shortages and restrictions. The authors argue that lowering Southwestern water use to sustainable levels will necessitate either very strong residential adaptation measures, or a combination of strong agricultural adaptation measures (including the elimination of some low-value crops) and moderate residential measures.

Four possible strategies to address the gap between water supply and demand are described:

  1. Increase supply through imports or desalination.
  2. Additional groundwater extraction.
  3. Planned reductions in water use. The report notes that this is the only viable solution.
  4. Unplanned shortages and harsh restrictions on water use if no other action is taken.

California is used as a case study of unsustainable water use. The authors find that unless the state implements adaptation measures, 7 out of 10 years will require water restrictions or additional overdraft by 2030, and every year will have a water shortfall by 2050. 

The report examines both state- and county-level water supply, use, and demand data, ensuring a level of detail intermediate between regional generalizations and local case studies. The analysis allows consideration of climate policy by examining the difference between a high-emission and a low-emission climate scenario.



Publication Date: February 2011

Authors or Affiliated Users:

  • Frank Ackerman
  • Elizabeth A. Stanton

Related Organizations:

  • Stockholm Environment Institute


Resource Category:

Resource Types:

  • Assessment
  • Case study

States Affected:


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