The Shrinking Colorado River

Photo by Bradley Udall, University of Colorado
Photo by Bradley Udall, University of Colorado

Arizona won't run out of water, but the amount of water available in the state is linked to the Colorado River flow.

The Central Arizona Project (CAP) pumps water from the river to homes, businesses, and farms in the state.

Low flow in the Colorado may lead to rationing amongst the states that share the river water.

These states are Arizona, New Mexico, California, Nevada, Utah, Colorado, and Wyoming.

A portion of the river water is also allotted to Mexico.

A new study including University of Arizona scientists explores how warmer global temperatures impact the Colorado River, and the news is not good.

The results of the study were published online Tuesday in the Bulletin of the American Meteorological Society.

The report called "Understanding Uncertainties in Future Colorado River Streamflow" looks at how warmer global temperatures associated with climate change will impact Colorado River flow by 2050.

UA News writes "The team's study does not provide new estimates of future annual flows of the Colorado River. Instead, it provides context for comparing the various scientific studies and explains why the different types of previous studies produced different predictions."

The consensus is that the flow will be lower but by 'how much' is the big question in regards to Colorado River flow.

The estimated range is 6% to 45% lower.

"Even if the Colorado headwaters get no change in precipitation, the temperature increases – a sure bet – will drive lower flows in the river," said Jonathan Overpeck, a UA professor of Geoscience and Atmospheric Sciences.

Hotter temperatures mean more evaporation, which leads to less water stored in reservoirs like Lake Powell and Lake Mead.

"It's surprising to me how much temperature increases alone will decrease flow in the Colorado," said Overpeck.

Lead author Julie Vano, who recently received a PhD from the University of Washington, said, "The different estimates have led to a lot of frustration. This paper puts all the studies in a single framework and identifies how they are connected."

While the numbers vary widely the science is important for water managers.

They can plan for the worst case scenario possible in the future.