and water scarcity are likely to be key impacts of climate change in the American Southwest region in the future, according to Dr. Glen MacDonald
of the University of California, Los Angeles, an expert on climate and sustainability in the arid Southwest. He recently visited the University of Georgia and presented a lecture entitled “It’s a Dry Heat – Climate Warming and Perfect Drought in the Southwest,” upon which the following is based.
MacDonald noted that with a regional population of around 19 million people and fairly low annual average precipitation, Los Angeles is dependent on the Colorado River for its water. He argued that when the river’s water was allocated among Western and Southwestern states in 1922, allocation decisions were made based on records from 1900-1920, which is now seen as an unusually wet period. Given subsequent droughts and increased population and water demand, as well as increasing regional temperatures since 1900, according to MacDonald, it appears that river water quantities were misallocated, leading to today’s situation: The Colorado River does not have a functioning delta and is a victim of overuse. (A compelling article about the plight of the Colorado River was published by Smithsonian magazine in 2010
MacDonald defined what he terms “perfect droughts” — or periods when low precipitation levels occur on top of low river flows — a convergence that can have serious consequences. Paleoclimatic records, such as tree rings, provide data on past climate conditions and indicate that there have been earlier extended droughts in the Southwest, such as one lasting 50 years in the 12th century, according to research by MacDonald and others. His studies indicate that the region has been experiencing another extended “perfect drought” since the year 2000, one that theoretically could last just as long as, or longer than, previous droughts. (His findings were published in the journal Proceedings of the National Academy of Sciences in 2010.)
With the Southwest experiencing the greatest temperature increase, the already critical drought situation is exacerbated, according to the speaker. Los Angeles built significant infrastructure for storing water in the early 20th century, so the city and its residents have been somewhat insulated from cycles of water scarcity, he said. However, despite the existing infrastructure, levels in Lake Mead
, an important reservoir serving Los Angeles and other cities, have dropped precipitously since 2000, and MacDonald expects the drought to continue.
With MacDonald’s unique perspective on climate change and drought in the American Southwest, the importance of taking action to enhance sustainability and protect our vital natural resources becomes even more urgent. The Southwest is just one example of a region affected by climate and environmental changes that are occurring around the world. Work such as MacDonald’s is critical in making us aware of the magnitude, scale and likely consequences of these changes.
Resource material: MacDonald, Glen M. 2010. Water, climate change, and sustainability in the southwest. Proceedings of the National Academy of Sciences 107(50): 21256-21262.