UA Scientist Warns Congressional Committee on Threats to Colorado River Basin

Jonathan Overpeck, co-director of the UA Institute of the Environment, told visiting Congressmen how human and natural events might well lead to protracted droughts in the region.
May 29, 2009
Stormwater flows from the roof of the Architecture Building into the Underwood Sonoran Garden on the north side of campus.
Stormwater flows from the roof of the Architecture Building into the Underwood Sonoran Garden on the north side of campus.

A "perfect storm" of population growth, drought and climate change threatens residents of the Colorado Basin, according to a University of Arizona researcher.

Jonathan Overpeck, co-director of the Institute for Environment and Society at the UA and a professor of geosciences and atmospheric sciences, told U.S. Rep. Raul Grijalva, D-Ariz., and others on the House Subcommittee on Water and Power on Wednesday that "this storm has both natural and human causes, and it requires urgent and sustained action by the federal government, states, universities and their partners to ensure that the basin, and all that depends on it, weathers the storm."

Overpeck said recent science suggests all three components of the storm are even more serious threats for the future and said two broad solutions working in tandem are required to deal with it.

One is mitigating climate change through reducing greenhouse gas emissions. The other is developing the capacity to adapt to climate variability and climate change in the future, especially drought, a persistent threat in the Southwest. Overpeck said special attention should go toward developing renewable energy resources like solar and wind.

Historic droughts in the Southwest during the 1950s and since 1999, he said, "pale in comparison" with megadroughts, recorded in tree rings, that have plagued the region over the last two millennia.

"For example," he told the congressmen, "the period A.D. 1130 to 1300 was characterized by 170 years of frequent severe drought in much of the western U.S., particularly in the Colorado River Basin.

"Even though the drought since 1999 has caused the major reservoirs on the Colorado River to decrease from full to half-full in only a couple of years, this drought is minor in a long-term context," he said.

Overpeck also said climate scientists currently are unable to predict the occurrence of such droughts with any confidence. What they do know, he said, is that the Lower Colorado Basin is regularly hit by multiyear, and even multidecade drought, and in all likelihood the region will experience such devastatingly severe droughts in the future. The longest droughts in North America, such as those during the medieval era, coincided periods of above-average temperatures.

Evidence from climate models also points to human activity as the source of changes in vegetation patterns and wildfire frequency. Overpeck said the bottom line is that the Lower Colorado River and neighboring regions could become the most ecologically threatened systems in the U.S. The paradox is that even though there would be less water, rainfall, when it happens, could be more intense and could cause more flooding. 

The twofold solution, Overpeck told the committee, requires a significant reduction in carbon dioxide and other greenhouse gas emissions. "Reductions by 2050 to levels 80 percent below 1990 levels is a good target," he said, adding that the Southwest has "the greatest power potential in the nation and has significant wind assets that can be tapped to curb emissions."

The second step is a 10-year, $200 million "federal stakeholder-driven science and services program" to create the knowledge and the access to that knowledge that decision makers could use to plan for future adaptations.

The program would be similar to the current Regional Integrated Sciences and Assessments model funded by the National Oceanic and Atmospheric Administration. That model incorporates research from university-based laboratories such as those at the UA, as well as federal laboratories.

"Not only would such a science and services program help avert future water conflict among states, Native nations and Mexico, it would also provide the capacity to deal with other implications of continued population increases, drought and climate change: threats to the region's ecosystems, public health, agriculture, ranching, air and water quality and much more," he said.