Change comes hard to Western water policy. The Prior Appropriation Doctrine, interstate compacts, groundwater law, the "law of the river" -- all of these seem set in stone in the minds of the region's policymakers.  Of course, the West's rivers aren't bound by such a static existence.  Indeed, they are changing in fundamental ways, opening a wide chasm between our water policy and our water sources.  This is particularly true for the Colorado River Basin.

Climate scientists are predicting a 10-to-30 percent reduction in flow for the Colorado -- a stark contrast to the rosy assumptions that underlay the Colorado River Compact when it was signed 88 years ago.  Researchers from the Scripps Institution of Oceanography recently predicted that Lakes Mead and Powell have a 50 percent chance of going dry by 2021. These days, Lake Mead is at 45 percent capacity and Lake Powell is at 57 percent capacity.

Farther south, water shortages are predicted for northern Arizona communities, including Flagstaff, by 2050.  The Central Arizona Project, which provides water to Phoenix and Tucson, may run short of water as early as 2012.

And farther downstream, Mexico is looking at a disaster along its stretch of the river due to inadequate flows, prompting one Mexican official to declare, "We are clearly on a collision course with a catastrophe," according to the Los Angeles Times.

Then there are the numerous environmental problems in the basin.  Six aquatic species are threatened or endangered, though the invasive quagga mussels are doing just fine.  The river corridor in the Grand Canyon, deprived of sediment and choked with tamarisk, is dying; the river's delta is already on its deathbed.  The Colorado is plagued by water quality problems, especially salinity, perchlorate rocket fuel, runoff from agriculture and inadequate sewage treatment.

The shortage of surface water has pushed some communities to mine groundwater. Communities as diverse as Tucson, Ariz., Las Vegas, Nev., and Cedar City, Utah, are experiencing subsidence because of their excessive withdrawals of groundwater.

The sediment that once was the lifeblood of the river now forms a giant plug at the junction of Cataract Canyon and Glen Canyon.  It is simply a matter of time before Lake Powell becomes the world's largest mud catchment, rendering the 710-foot-tall dam useless.

Water shortages in the Lower Basin will be greatly exacerbated by proposals to build giant pipelines. Las Vegas, which gets 90 percent of its water from Lake Mead, wants to build a $4 billion pipeline to central Nevada to pump groundwater from beneath several valleys in the Great Basin.  This 300-mile pipeline is likely to lower groundwater levels, threatening a national park, national wildlife refuges, an Indian reservation, and local ranchers and farmers.  The resulting loss of surface flora is not just a cosmetic problem; it could result in huge dust storms that blanket Salt Lake City.

St. George, Utah, sort of a Las Vegas wannabe in terms of growth rate (but without the sinful fun), wants to build a billion-dollar pipeline that sucks water out of Lake Powell -- despite the imminent demise of the lake. In the Upper Basin, Aaron Million, with dreams to match his name, wants to build a 560-mile pipeline from the Green River to Colorado's Front Range and divert 250,000 acre-feet. In addition to these proposed pipelines, the city of Denver wants to dramatically increase the water it pumps out of the Colorado River Basin, and the state of Wyoming recently created a new state "Dam and Reservoir Section" to investigate the feasibility of new diversions on the Green River.

These grandiose schemes for new diversions are not "the way of the future," but rather the last gasp of a dying water ethos.  The myriad problems of the Colorado River point to one inescapable conclusion: Western water policy is hopelessly, irrevocably unsustainable.  Policies that once created stability are now an albatross, preventing the West from making fundamental changes in the way it allocates and uses its water.

It is time for a new era in water management. The first step requires dispensing with the absurd notion that infinite growth can take place in a region with severely constrained resources.

The second step is to realize that agriculture, which uses the lion's share of the river, is going to take a big hit.  Many of the crops grown in the basin are low value, such as hay, or are commodity crops that are already over-produced in the United States.

And the third step requires improving the quality of the water by forcing all polluters to clean up their mess. That includes agriculture, mining and municipalities with inadequate urban treatment. These changes will not be easy -- it's like prescribing a root canal for an entire region without offering nitrous oxide.  But the longer we wait, the more difficult it will be to make the transition to a policy that meets the reasonable needs of cities, a service economy and the age of limits.

Dan McCool is a contributor to Writers on the Range, a service of High Country News (hcn.org). He is a political science professor and director of environmental studies at the University of Utah in Salt Lake City.