Higher temperatures and lower water levels are causing states to rethink 20th century infrastructure
By Allen Best | American Planning Association
The hundred feet of bleached sandstone walls of Glen Canyon exposed by the receding waters of Lake Powell starkly illustrates the conundrum of water infrastructure in western states and the effects of a changing climate. Completed in 1963, the construction of Glen Canyon Dam across the Colorado River in the Utah desert was a landmark in the resolute 20th century effort to harness rivers of the West to provide water for irrigation — and, indirectly, for expanding cities — and hydroelectric power for both.
Today, the dam delivers 1,320 megawatts of low-cost, low-carbon hydroelectric generation to farms and homes as far away as Nebraska. The reservoir, the nation’s second largest, is among 260 on the Colorado River and its tributaries that store and regulate flows in a vast plumbing system supporting a population of 40 million people from Denver to San Diego — cities outside of the river basin itself — and some of our nation’s most productive agricultural areas.
Population growth alone puts pressure on this 20th century infrastructure. Southwestern states grew 37 percent from 1990 to 2010, with no end in sight. Now comes clear evidence of climbing temperatures and hints at shifting precipitation patterns.
Lake Powell, nearly full at the start of this century, is projected to end 2018 at 43 percent of capacity after another year of decreased runoff on the Colorado River. Subpar runoff has been more common than not this century, but unlike droughts of the past that were caused by reduced precipitation, some climate scientists say that warming temperatures have caused more than half the declined flows, due to evaporation and transpiration (when plants absorb water through their roots and then emit water vapor through pores in their leaves).
But Powell is just a chapter in a larger story. It is operated in tandem with Lake Mead, the nation’s largest reservoir, which is 300 miles downstream, below the Grand Canyon. Together, the two reservoirs can store 50 million acre-feet of water. (Smaller reservoirs in the seven basin states can store an additional 10 million acre-feet.)
