Earth Notes
8:44 am
Wed May 8, 2013

Earth Notes: Glen Canyon Dam - The Future

Those who manage and use reservoirs in the western United States are used to cycles of boom and bust: wet periods fill reservoirs, while droughts empty them. But as the Southwest enters what looks like an uncertain future of climate change, there's evidence that Lake Powell may be in for a particularly hard time.

Glen Canyon Dam
Credit National Park Service

That's because climatologists have developed detailed models that project how regional climate will change as the Earth warms. And those models are in widespread agreement that the Southwest is likely to grow drier.

That's not necessarily due to less water coming from the atmosphere. Climatologists think that overall amounts of precipitation may not change much in the Southwest or in the high mountains that feed the Colorado.

But they are in agreement that temperatures are on the rise. That means less precipitation falls as snow, and more as rain, which means faster runoff and more erosion. Higher temperatures also increase evaporation.

Together, these factors may reduce the Colorado's supply by at least 10 percent within the next two decades. Allocating a diminished water supply to the 40 million people who depend on the Colorado will be tough.

The numbers suggest that Lake Powell will shrink further. It's simply not as vital for water deliveries as Lake Mead, near Las Vegas. It's likely that the future Lake Powell is going to show a lot more of its desert roots: mudflats, windblown sand and sandstone walls, all surrounding a diminished blue oasis.