A study finds climate change will further reduce Colorado River flows.

Global warming will worsen drought and reduce flows on the Colorado River, a key water source for Southern California and six other Western states.

The study, prepared by a National Research Council committee, paints a sobering picture of the future as the water needs of a rapidly expanding population test the limits of a river system further strained by the effects of climate change.

The authors concluded that there was no easy solution. Such measures as conservation, desalination and water recycling will all help, they said, but won't offer a panacea.

The report, which examined climate modeling and tree-ring data, reaffirms a more pessimistic assessment of river hydrology that has emerged in recent years.

Scientists have concluded that historically the Colorado River system, which supplies water to 25 million people and several million acres of crop and ranch land, has been drier and more prone to severe drought than was the case in the early 20th century, when the river's flows were divvied up among the seven states in the basin.

That period, it turns out, was unusually wet, prompting an overly generous estimate of how much water would be available to farms and cities. Ancient tree rings, which provide graphic evidence of past precipitation patterns, indicate it had been three centuries since the basin was last awash in that much water.