Here is our initial post on the this Interior Department Study which included the following conclusions
Lack of calibration of the hydrologic models is a real issue that needs to be addressed and should be addressed before these models are used in future assessments. Reclamation will (a) refine the VIC application and/or (b) introduce more appropriate hydrologic models. However, before implementing west-wide calibration efforts, it also is important to assess the fitness of the chosen model structure for some geographic situations, particularly basins where ground water interactions with surface water may be an important process and not well simulated in VIC.AND
6.1.2 Global Climate SimulationYet we have media outlets and authority figures representing this report as being evidence on which changes to policies should be made.
While the activity presented in this report considers climate projections produced by state-of-the-art coupled ocean-atmosphere climate models and even though these models have shown an ability to simulate the influence of increasing GHG emissions on global climate (IPCC 2007), there are still uncertainties about the scientific understanding of physical processes that affect climate; how to represent such processes in climate models (e.g., atmospheric circulation, clouds, ocean circulation, deep ocean heat update, ice sheet dynamics, sea level, land cover effects from water cycle, vegetative other biological changes); and how to do so in a mathematically efficiently manner given computational limitations
...Temperatures could rise 5 degrees to 7 degrees this century, increasing evaporation, and the spring snow pack will drop sharply in much of the West, changing the timing of peak runoff, which is crucial for the state's irrigated agriculture....
...The report predicts that precipitation in the river's upper reaches will increase by a few percentage points in the mid- and late century, although that would be offset by a slight drop in runoff associated with warmer temperatures and more water consumption by plants.
Farther down the river, at Lee's Ferry, runoff could decline by 8.5% in the 2050s, the report suggests.
The greatest drop is predicted for the Rio Grande in New Mexico, where stream flow could shrink by nearly a fifth by the last quarter of the century.
"The status quo is going to change," U.S. Bureau of Reclamation Commissioner Michael L. Connor said. "We need to take action now to plan for those changes that are occurring."
Pasadena Star News
New report says climate change likely to make water more scarce[excerpts]
..Interior Secretary Ken Salazar said the report will help officials understand the long-term effects of climate change on Western water supplies and will be the foundation for efforts to develop strategies for sustainable water management
The report notes that projected changes in temperature and precipitation are likely to alter the timing and quantity of stream flows in all Western river basins, with increased flooding possible in the winter due to early snowmelt and water shortages in the summer due to reductions in spring and summer runoffs.....
.... All eight basins should see an increase in temperature of about 5 degrees to 7 degrees Fahrenheit by the end of the century, the report says.
Four basins will see an increase in overall precipitation by 2050: the Upper Colorado, Columbia, Missouri and Sacramento, while four will see a decrease: the Lower Colorado, Rio Grande, San Joaquin and Truckee.
Reductions in spring and summer runoffs could lead to a drop in water supply in six of the eight basins, the report said.
Local officials said the report shows the need for more water conservation.
"It just means that it's all the more important for us to conserve water and be independent of imported water supplies as much as we can," said Carol Williams, executive director for the Main San Gabriel Basin Watermaster.....
....MWD also is looking at solutions. One possibility would be to build a desalinization plant in Mexico that would free up Colorado River water for the United States, including Southern California, he said.
One problem could be the expense. Water from such a plant would cost $1,500 per acre-foot, in contrast to the water bank's cost estimated at $450 per acre-foot that also includes pumping costs, according to Hazencamp.
Updates as found
Climate change to hit American West water supply
...This steep drop in stream flow is projected for parts of the West that have seen marked increases in population and droughts over recent decades, Interior Secretary Ken Salazar said in a telephone briefing.
"These changes will directly affect the West's water supplies, which are already stretched in meeting demands for drinking, irrigating crops, generating electricity and filling our lakes and aquifers for activities like fishing, boating and to power our economy," he said...
..."Climate change will add to the challenges we face, which will be felt first in the Western United States," said Anne Castle, the Interior Department's assistant secretary for science and water. She noted that some of the fastest population growth has occurred in the driest areas, including parts of Nevada, Arizona, Utah, Idaho and Texas.
"Water is on the leading edge of climate change, so many of these basins have already experienced significant ... decreases to water supply," Castle said.
also Lompoc Record