LAS VEGAS - December 4, 2008 - A new study by UNLV researchers revealed that increasing temperatures in the Colorado River Basin over the past 55 years have changed the timing and magnitude of the basin's streamflow - further evidence that climate change is impacting water resources in the region.

The study, which appeared in the October 2008 issue of the Journal of Hydrometeorology, found that steadily increasing temperatures in the Colorado River Basin from 1951-2005 have affected the character of precipitation over the area. The result is more frequent rainfall and less frequent snowfall, leading to a decrease in snowpack and snowmelt in the region. The ability to forecast water flow into the Colorado River is important to regional water resource managers, who need accurate inflow forecasts to plan both annual and long-term system operations.

"Snowfall, particularly in the upper part of the basin, is important as it replenishes mountain storage and is a key runoff source during the spring," said Tom Piechota, UNLV Director of Sustainability and Multidisciplinary Research and associate professor in Civil and Environmental Engineering. "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."

Piechota conducted the study with W. Paul Miller, a UNLV graduate student and hydrologic engineer student trainee with the federal Bureau of Reclamation in Boulder City, Nev.

Using historical temperature and precipitation data from the National Climate Data Center (NCDC) and records of natural runoff from the Bureau of Reclamation, the team identified a consistent increase in temperatures over the Colorado River Basin, increased river flows in the late fall and winter months and decreased river flows in the spring and summer months.

While this study does not explicitly compare trends in snowpack with streamflow trends, it is hypothesized that increased temperature over the basin has resulted in increased rainfall frequency and earlier snowmelt leading to a decrease in streamflow during the peak runoff season (April through July). Future research will evaluate this hypothesis.

"We support a multi-faceted research and development program to better understand the potential impacts of climate change on the Colorado River Basin's water resources and this study has added a significant piece to that understanding," said Steve Hvinden, Area Manager of Reclamation's Boulder Canyon Operations Office.

The Colorado River Basin includes portions of seven states - Colorado, Wyoming, Utah, New Mexico, California, Nevada, and Arizona - and encompasses approximately 242,900 square miles. Runoff from snowmelt in the high mountains in the upper part of the basin is the primary water supply source for the Colorado River.

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