By Paul Larmer

Since Christmas, an almost continuous stream of Pacific moisture has raced over Colorado and much of the West, dumping rain in the valleys and heavy snows in the mountains. The sun and crystalline blue skies I brag about to my non-Western friends and relatives have only made rare appearances in the narrow seams between storms.

Frankly, it's been a little depressing. But water-watchers in the West are almost giddy with joy: Every week, our local papers run stories with cheerful quotes from forecasters proclaiming that the drought gripping the region for the past five years may be broken.

" Every string of fantastic years has to start with one," Tom Pagano, a water supply forecaster for the U.S. Department of Agriculture recently told The Associated Press, "and we can only hope this is it."

Early January surveys of snowpack show that the Colorado River Basin, which gathers runoff from Wyoming to Southern California, will receive 98 percent of "normal" precipitation this year. If the rest of the winter meets historic averages, Lake Mead and Lake Powell, the West's most massive reservoirs which have shrunk over the past five years to 56 percent and 36 percent of capacity, respectively, will rise.

That's good news not only for the recreationists who love to boat in the desert, but also for the tens of millions of people who rely on the river for agricultural and drinking waters, including farmers in Arizona and urbanites in Las Vegas. But I wouldn't bet on the reservoirs filling up just yet.

As reported in High Country News this month, scientists at the University of Arizona have discovered through analysis of the growth rings of trees that drought is a persistent visitor to the West. Over the past 500 years, a half-dozen major droughts, some lasting many decades, have struck the Colorado River Basin, according to research from the university's Laboratory of Tree-Ring Research. So the current drought could last a long while, whether it is interrupted by an occasional wet year or not.

Wet-weather optimists would be wise to listen to the scientists, or at least remember the wisdom of explorer John Wesley Powell, whose name graces the massive reservoir on the Utah-Arizona border. Powell's 1878 report to Congress on the arid lands of the West -- reprinted last year by the University of Nebraska Press --is "a sober and foresighted warning about the consequences of trying to impose on a dry country the habits that have been formed in a wet one," wrote Wallace Stegner in his introduction to the book.

Powell and Stegner knew that droughts would define the development of the West. What they couldn't know was that our rapid combustion of the planet's fossil fuels could make the dry periods more lengthy and intense. Over the past several years, scientists studying tree rings, glaciers, corals and lake- and sea-bed sediments have discovered that atmospheric temperatures have risen sharply since the early 1900s, when the use of fossil fuels took a dramatic turn upward. Warmer temperatures means earlier melting of the snowpack, where the West's water is stored, more evaporation from reservoirs, and dryer soil conditions, all of which spell drought.

So what should Western farmers, urban planners, developers, conservationists and public officals do? They should plan now for drought and rethink water-allocation systems that no longer make sense.

Fortunately that's what some are doing. Last fall, Arizona drafted its first-ever drought plan, which calls for some modest first steps, including mandatory water conservation for state agencies and universities. The federal government is also weighing in: The Interior Department, which includes the agency that built much of the West's water storage and delivery systems, the Bureau of Reclamation, has ordered the seven states that share Colorado River water to write a plan for managing a shortage of water.

States with more water than they can currently use, such as Arizona, will have to share with those that are running short, such as Nevada. Water hoarding and wasting will not be tolerated in a world of prolonged drought.

The plan is due in April, and is a sign that the message of the scientists -- reinforced by five years of warm temperatures, drought and wildfire -- has begun to be heard.

Another dry year or two, and we might actually change our behavior. This is why I hope it stops raining and snowing soon.