Lake Powell gets an A for boating and a D for water storage
It's fun in the sun as usual at Lake Powell, as this summer follows another in a pattern of drought in the 21st century. But though the reservoir has plenty of water for boating, its primary purpose is to store water for the American Southwest. By that criterion, Lake Powell is a bust at 52 percent of capacity.
Hopes for more storage were high only six months ago. Storms in Colorado early last winter left record snowfalls, and it looked to be an average or even better year across the Colorado River Basin. But winter retired early, as has become its habit, and runoff was again substandard, at only 75 percent of average.
Aridity in the Southwest has always been axiomatic, nearly a point of pride. It's how we define the region and, by extension, ourselves. Even so, fresh evidence continues to arrive that forces us to redefine our aridity.
The most recent testimony is a study of tree rings in the river basin, and it reveals that extended droughts were far more common in the past. For example, various claims have been made in recent years that our current drought is the worst in hundreds of years. In fact, according to tree rings at Lees Ferry, at the mouth of the Grand Canyon, the annual flow of the river during 1844-1848 was lower than the observed flow of 1999-2004.
Trees also tell of many extended droughts. Eight periods between 1536 and 1850 may have been as dry as the recent drought, according to the work by Western climate specialists Connie A. Woodhouse, Stephen T. Gray, and David M. Meko. They also found evidence that droughts of the past have been longer than the drought of recent years — perhaps decades long. The tree rings, they said in a report issued earlier this year, "demonstrate that severe, sustained droughts are a defining feature of the Upper Colorado River hydroclimate."
These more severe, sustained droughts of the distant past are in sharp contrast with the anomalously wet 20th century. Wettest of the wet was the period from 1910 to 1920, the basis for the Colorado River Compact of 1922, which apportions the waters among the seven states of the river basin. Another particularly wet period came during the 1980s and 1990s. In other words, our cheerful understanding of aridity in the Southwest has been that of a glass half-full.
This view into the past is important given two trends of the present and future. First is the great population growth under way. By one estimate, the Colorado River already serves 25 million people, from Cheyenne to San Diego and from Albuquerque to Salt Lake City. Several Colorado River Basin states led the nation in population growth during the 1990s, and that trend is expected to continue.
Global warming is a second consideration. Computer models are only now being delivered that pick up the bumpiness of the Rocky Mountains and the Sierra Nevada. Earlier versions were far too coarse. Increased greenhouse gas emissions may also change the climate of the West. That said, all computer modeling predicts shorter winters, earlier runoff and higher temperatures. That means less snow in the high country — the source of 80 percent of the water in the West — and the snow is less likely to linger into summer. That means more water in low-lying reservoirs where it can evaporate more readily.
Looking both backward aided by tree rings and forward given both demographic projections and greenhouse gas theory, the water situation in the West is likely to get much more dicey. On both counts, we need a revised appreciation for aridity in the American Southwest.
Meanwhile, Lake Powell has pulled back from the brink. In early 2005, water managers were fretting that the reservoir, by then only 33 percent full, would be nearly empty by now, a bathtub with ugly rings indicating an earlier time of plenty.
But for many Lake Powell boasters, it's just fine as it is. Jim Mullen, a mechanic in Glenwood Springs, Colo., visited Powell again in June, and reported a delightful variety of beaches available due to the lower water level. "When it's full, you have no place to camp unless you're on a house boat," he said. "If I never see it fill again, I would be happy."
For some, a glass half-full is still as good as it gets.