Eleven years of low flows and growing consumption are draining the reservoir. Meanwhile, much of the rest of the West is slowly aridifying too.UPDATE, SUNDAY 10/17/10: AS OF ABOUT 11 a.m. (MST) TODAY, LAKE MEAD HAD DROPPED TO A RECORD LOW LEVEL. AS I WRITE THIS AT 7 P.M., THE LAKE STANDS AT 1083.15 FT, FOUR TENTHS OF AN INCH LOWER THAN THE PREVIOUS RECORD LOW, SET IN 1956. (I’ve updated the headline to reflect this. But I’ve left the original lede to the story as is.) Also, please check out John Fleck’s excellent post about this. He was there today when it happened and got some interesting reactions from tourists.
In as little as the next few days, Lake Mead, the giant reservoir on the Colorado River that serves millions of water users, will drop to record low levels.
To be more precise, it is all but inevitable that its elevation above sea level will drop below 1,083.19 feet, the historic low reached in 1956. And when that happens, the reservoir will be at a level that has not been seen since the reservoir was filling up in the 1930s. (For the current level of Lake Mead, click here.)
Lake Mead is, in essence, a giant hydrological bank account from which California, Nevada and Arizona — the “lower basin” states of the Colorado River — make withdrawals to slake the thirst of cities like Las Vegas, and millions of acres of farmland. But 11 years of dry conditions, combined with ever growing demand, have steadily drained Lake Mead.
If it continues to drop below a crucial trigger point of 1,075 feet, Bureau of Reclamation managers have plans to release extra water from Lake Powell — the reservoir upstream on the Colorado created by the Glenn Canyon Dam. They hope this will tide the lower basin states over until wetter conditions return to the Colorado Basin. (For a map of the basin, click on the image at left.)
But will wetter conditions return? Climate scientists caution that droughts are likely to become even more intense and longer lasting as concentrations of heat-trapping carbon dioxide in the atmosphere continue to rise. In fact, it’s possible that water levels will never recover.
“My hydrology friends in the Southwest tell me that they don’t expect Lake Mead or Lake Powell ever to fill again,” says Steve Running, an ecologist at the University of Montana who studies the impacts of climate change on ecosystems. “And that’s the good news.” (For more on this issue, check out the second half of this post.)
Las Vegas is now hedging its bets by tunneling beneath Lake Mead to install a new intake system. This would allow southern Nevada to continue drawing water from the reservoir even if the lake drops below the level of existing intakes.
Meanwhile, a drop below 1,075 would trigger a series of actions aimed at conserving water.
“There are many people who think we could hit 1075 quite easily next year,” says Brad Udall, director of the Western Water Assessment at the University of Colorado. “Arizona would take most of the shortage. Nevada a little.”
What would that mean for residents of those states? “No one is going to dry up, not be able take showers or drink water. But we’re going to have to think long and hard about 19th century water law, which in some sense is what’s at work here, 20th century infrastructure, and 21st century population and climate change.”
Over the past few weeks I’ve interviewed a number experts about the significance of what’s happening in the Colorado Basin — and in The West generally. My longest and most detailed interview was with Udall. The full interview with him ran on “How On Earth,” KGNU FM’s weekly science show, earlier this week. To listen to the interview, click here and skip forward in the audio to about 12 minutes.
Below are some experts from that interview, as well as comments and information from Steve Running.
To start the interview with Udall, I asked what significance he placed on the record low Lake Mead is about to hit.
. . . what you’re really seeing here is a combination of drought and an overuse problem amongst the three three lower basin states of California, Nevada and Arizona. And that overuse problem historically has been covered up by a little extra water that flows down from Colorado and the upper basin states. But over the last 11 years, with the most serious drought on record, that water hasn’t been there, and so the overuse problem has become readily apparent.
To what degree is climate change implicated in the 11 years of drought that has left Lake Mead so low?
The way science and statistics work is that there’s a really high bar set to say, ‘Okay, this particular event is actually climate change and not just natural variability.’ In fact that bar is so high, frequently all you can say is, hey, this is consistent with what we think climate change will bring. I think this is in many ways where we are in the Colorado River. Although there have been some attribution studies suggesting that things like timing of runoff, which is occurring earlier, temperatures we’re seeing, some reductions in snow pack, are statistically significant.
But I think these are very early studies, and its a little hard to say with certainty that . . . what we’ve seen over the last 11 years — which is the worst historical drought on record by far — is due to climate change. What you can say is that over the last 11 years, temperatures [have been] 1.6 degrees higher than normal . . . And while that doesn’t sound like a lot, it actually is a lot when you measure it over the whole basin. And I think it’s pretty easy to say that those higher temperatures have to be related to less water we’ve seen in the system.
During the current drought, we’ve seen a roughly 20 percent reduction in flow in the lower Colorado River. The next worst drought was in the 1950s, which saw a 17 percent decline in flow. That difference in flows between the present and the 1950s may not seem like a lot, Udall says, but over 11 years it amounts to the loss of about 5 million acre feet — “or roughly one third of the flow that occurs in a year.”
Nature is perfectly capable of producing even worse droughts. In fact, tree ring studies show that droughts of the intensity we’re experiencing now lasted for as many as 60 years back in the 11oo’s, according to Udall.
A 60-year period is an enormously long period of time relative to the 11-year period we’ve been in. So the historical droughts … are far worse than what we’ve seen, and I think there is reason to believe they could occur again either under climate change, or obviously without climate change. But I guess the bottom line is this is a very serious drought . . . [and] if it were to continue, there would be some very serious consequences for the Lower Basin with regard to their water use.
What has happened to flows along the Colorado is reflective of what’s happening in the interior West generally.
“Throughout the West we are slowly arridifying,” says Steve Running of the University of Montana. “We are heading toward a more arid climate overall.”
Monitoring of the flow of streams and rivers in Running’s own state, Montana, shows that the steadily drying climate is having an impact, particularly in August, when flow is at its lowest at the end of summer. “The trend for every single river studied is down on order of 30 to 40 percent,” he says. “We are dewatering our rivers right now at a very alarming rate.”
Update 10/18/10, 8 a.m.: A new paper in the Journal Science finds that reductions in flows of the world’s rivers is shortening food chains by eliminating top predators like many large-bodied fish. Click here for the abstract, and here for a Eurekalert press release about the research.
What can we expect moving forward? With climate change, might we be at significant risk of more drought like the one that has dropped Lake Mead’s level so low?
“We think you could lose 10 to 20 percent of flow on Colorado by 2050 . . . so 40 years from now,” Udall says. (Other estimates suggests flows could drop even more. See the map below.) Those reductions in flows are likely to come from increases in temperature and some decreases in precipitation. He notes that the Colorado headwaters happen to sit in an area of world that is particularly prone to drought. And climate change modeling suggest that with continued increases in atmospheric concentrations of greenhouse gases, dry areas are likely to get still drier.
As a result, many regions of the world will probably have to cope with increased aridity, as the map below shows. The map is from the IPCC report “Climate Change and Water,” and it depicts projected changes in annual runoff in river basins around the world, based on the output of an ensemble of 12 climate models:
These projections are predicated on the IPCC’s A1B scenario, which features very rapid economic growth, a global population that peaks in mid-century and declines thereafter, and rapid introduction of new and more efficient technologies. (White areas show areas of significant disagreement on the sign of change between models; hatched areas indicate where more than 90% of models agree on the sign of change.)
As the map suggests, even if the world manages to rapidly introduce energy technologies that help us get off carbon-based energy, many areas of the world are likely to get drier by 40 percent or more.
“When you look around the planet with regard to water, places like India and China are particularly at risk given growing population and use of water for food and all these competing uses,” Udall says.
During the next century, one of the most pressing environmental issues we’ll face will be “the intersection of carbon and climate change with all these other problems. And water is one of the first ones that’s arising. The Colorado River Basin is the classic case in the United States.”