Was 20th Century Unusually Wet?

ByABC News
October 19, 2004, 9:28 AM

Oct. 20, 2004 -- -- The American Southwest is in the seventh year of a drought that could have a profound impact across the entire country and, in the end, stand as a stark monument to human exploitation of a land of limited resources.

Droughts have struck that region often down through the centuries, contributing to the collapse of entire societies like that of the remarkable Anasazi Indians who built six-story housing developments hundreds of years ago and wide roads in a region with no vehicles.

But this drought could be even worse, plaguing the most rapidly growing area in North America. Several lines of evidence suggest that the past few decades have been wetter than normal, and severe droughts lasting tens of years are more likely the norm rather than the exception.

The story is told in tree ring records that tell of the variation in growth of trees over hundreds of years due primarily to rainfall, and soil analysis that tells of the presence of charcoal and thus vegetation, and records of changing ocean temperatures as far away as the North Atlantic. They all point in the same direction.

In a word, scientists are already starting to call it a "megadrought." But more than likely it's a return to normal weather patterns for a huge chunk of the nation ranging from the snow-covered peaks of the Colorado plateau to the arid deserts of the Southwest.

Someday, not too far down the road, water may be more valuable than oil in megalopolises from Los Angeles to Las Vegas to Phoenix to Denver and beyond. Even a couple of years of normal rainfall, if they come soon, won't change the fundamental fact that some very hard decisions are going to have to be made in the near future.

And adding to all of that is the concern voiced by many scientists that global warming will make the picture even bleaker.

The details lie along the entire route of the once mighty Colorado River that carved the Grand Canyon as it coursed down from the highlands toward Mexico, which it doesn't even reach any more. For decades water from the river has been siphoned off to reservoirs where it could be fed to the growing populations of the Southwest.