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Study of Climate Change Impacts on Water Shortages in U.S. Southwest

A recently released report claims that the effects of Climate Change will significantly contribute to water shortages in the U.S. Southwest in coming years. The Stockholm Environment Institute (SEI) has issued a study called “The Last Drop: Climate Change and the Southwest Water Crisis.” The study notes that even without the effects of climate change the Southwest faces a significant crisis in water supply. With climate change the crisis will worsen.

“A great deal is already known about water and climate change in the Southwest. For our purposes, the following are some of the most important findings:

-Climate change will worsen the region‟s water crisis even if, as some models predict, there is no change in total annual precipitation.
-Agriculture in the Southwest is almost completely dependent on irrigation; the greatest climate risk to agriculture is not the direct effect of temperature or precipitation on crops, but the potential lack of water for irrigation.
-Published estimates of the costs of climate impacts on water resources are in the tens of billions of dollars annually for the United States as a whole, or about $1 billion each for California and for the Colorado River basin.”

Some of the numbers reported in the study are:

“Taking into consideration only baseline growth of population and income, the Southwest‟s shortfall of water (today‟s overdraft plus additional water needed beyond today‟s annual rates, or green plus yellow in Figure 1) reaches 1,815 million acre feet over the 100-year period. Using the B1 climate assumptions – the least climate change that is still thought to be possible – the Southwest‟s shortfall grows to 2,096 million acre feet (green, yellow, and orange). Under the A2 climate assumptions – the temperature increase expected if the current trend in global greenhouse gas emissions continues – the shortfall reaches 2,253 million acre feet (adding the red segment). This shortfall must be met either from increases to supply (perhaps the most difficult and most expensive options as discussed below), additional groundwater withdrawals, or reductions to use – planned or unplanned.”

-Steven Silverberg