PHOENIX-
Shifts in climate could permanently reduce the flow of the Colorado River and expose millions of residents in some Western states to water shortages, according to scientists.
In a report released Wednesday by the National Research Council, scientists said population growth and drought also represent serious threats to the river.
More than 25 million people in seven states, including Arizona, rely on the Colorado River for water and power. The river also supports a diverse riparian system that has suffered as flows dropped.
The report said higher temperatures would melt snow too early, increase demand among water users and allow too much runoff to evaporate, in effect knocking the river out of its natural balance.
The scientists did not propose specific policy changes, but urged Western water managers to work together on new ideas and prepare to make difficult decisions about how water is used.
“The basin is going to face increasingly costly, controversial and unavoidable trade-off choices,” said Ernest Smerdon, a former dean of engineering at the University of Arizona and one of the report’s authors. “Our hope would be that the community and the decision-makers will have planned before crises occur.”
The report was commissioned by the U.S. Bureau of Reclamation, the Southern Nevada Water Authority and two California water agencies.
Citing several tree-ring studies, which helped write a hydrological history of the Colorado dating back more than 500 years, the scientists concluded that the river is more vulnerable to prolonged, intense droughts than previously thought.
The report said temperatures also have risen along the Colorado in recent years and have already affected snowmelt in some areas with long-term warming possibly shrinking the river’s flow and increasing demand.
Growing cities will force states to strike deals with farmers, but even that supply is limited, according to scientists.
The report said the combination of threats eventually will overwhelm the seven river states, which have struggled to produce a short-term drought plan.
