Over that period, warmer weather resulted in more frequent rainfall and less frequent snowfall, leading to a decrease in snowpack and snowmelt in the region.

"When rain occurs in place of snow, streamflow peaks earlier in the year and can make it challenging for water managers to assess resource availability," said Tom Piechota, UNLV director of sustainability and multidisciplinary research. "Warming by itself can change water supply. It's something to be concerned about."

The Colorado River is primarily fed by runoff from melting snow in the high mountains in the upper part of the basin.

The Las Vegas Valley gets 90 percent of its drinking water from the river, which also supplies tens of millions of people in Arizona, California, Colorado, New Mexico, Utah and Wyoming.

The UNLV study is further evidence that climate change has been affecting the river for some time.

Piechota authored it with W. Paul Miller, a UNLV graduate student who works with the federal Bureau of Reclamation in Boulder City.

Using historical temperature, precipitation and runoff data from 1951-2005, the researchers identified a consistent increase in temperatures over the Colorado River Basin. They also noted increased river flows in the late fall and winter months and decreased river flows in the spring and summer months.

Their findings were published in the October issue of the American Meteorological Society's Journal of Hydrometeorology.

Future research will seek to link the rising temperatures to an increase in rainfall and earlier snowmelt, leading to a drop in streamflow during what is now the peak runoff season of April through July.

The UNLV study was funded by the Bureau of Reclamation, the National Science Foundation and the National Oceanic and Atmospheric Administration.

Its findings come on the heels of dire predictions for the future of the Colorado.

A study released in February by the Scripps Institution of Oceanography in San Diego warned there is a 50 percent chance that Lake Mead, the river's largest reservoir, could run dry by 2021.

That prediction has since been challenged by other studies and regional climate models, but most scientists forecast less water for the river in the future.

Of course, Mother Nature will have the final say.

Piechota was in Boulder, Colo., for a meeting on Monday, and he got out just ahead of the snow. So far, he said, it looks as if the snowpack season is "off to a pretty good start."

Contact reporter Henry Brean at hbrean @reviewjournal.com or 702-383-0350.