Into thin air?
Global warming has spawned a call for new dams — but there may not be any water to fill them.
The dream of the infinitely expanding West is getting beaten over the head with an empty bucket. Flows in the Colorado River, which is now entering its eighth straight year of drought, will be less than half of average this year. In the Sierra Nevada, snowpack is just 46 percent of normal. And those numbers are likely to get even worse in the future, as droughts are amplified by global warming.
Now, water managers in the region are contemplating how to react, and new dams have been pitched as one possible response. In California, Gov. Arnold Schwarzenegger, R, announced on Jan. 9 that “with California’s booming population, and with the impact that global warming will cause to our snowpacks, we need more infrastructure.” Just two days later, California state Sen. Dave Cogdill, R, picked up the battle standard and introduced a bill to raise $4 billion in bond money for two new dams, saying, “We have to act now.”
Indeed, global warming is already changing the West’s waterscape. Average temperatures in the region have increased by about 2 degrees Fahrenheit since the 1970s. A greater portion of each year’s precipitation is falling as rain rather than snow, and snowpack — which serves as a natural, slow-release reservoir — is melting earlier than it used to; both changes are intensifying the pulse of winter and spring runoff.
Cogdill, who represents parts of the largely agricultural San Joaquin Valley, says that the continued loss of snowpack and the intensified bursts of seasonal runoff could exceed the storage capacity of California’s existing dams. “If you don’t do something about our ability to manage that water,” he says, “more and more of it will run into the ocean, and late in the year we’ll be in a real deficit.”
New dams can catch excess bursts of water when they come out of the mountains, then spread those flows throughout the year. But it is becoming clearer that, for the West as a whole, more dams may not stem future water crises. New climate projections are hinting that in the future, the region won’t just be warmer. It will also be drier.
Any effort to build more dams will be shadowed by the curse of diminishing returns. For one thing, there simply aren’t many places left to put a dam, either in California or in the West as a whole. One of the two proposed California dams would be built at Temperance Flat, in the Sierra foothills near Fresno, to catch floodwater in the San Joaquin River. Yet possible dam sites are so limited that the dam would have to be built in an existing reservoir called Millerton Lake. The second, Sites Reservoir, would be built in the hills on the western edge of the Sacramento Valley, and would hold water from the Sacramento River.
A very big question lurks behind the new-reservoir endeavor: While the dams are being pitched as part of a strategy to increase the reliability of California’s water supply, the reliability of the river flows needed to fill the new reservoirs is far from clear. In the case of Temperance Flat, for example, flow data from the past 57 years indicate that a dam could catch a considerable amount of water.
But past performance is no guarantee of future results. What will happen to river flows depends, in large part, on how much precipitation falls in a warming world. Michael Dettinger, a U.S. Geological Survey researcher at the Scripps Institute of Oceanography, has helped lead the way in assembling large “ensembles” that provide a composite view of various climate projections. Earlier projections, released about seven years ago, indicated that total precipitation in the West might actually increase with global warming. “Back then, the (climate-simulation model) that got most of the focus made the West just incredibly wet: It doubled the amount of precipitation, and more in some places,” Dettinger says. Now, “a lot of people think that was virtually a computer bug.”
In the years since, an increasing number of scientists have focused their efforts on climate change, largely in support of the most recent Intergovernmental Panel on Climate Change assessment, released this spring. “It’s still unsettled,” says Dettinger, “but as people have tinkered with their models and made the models better, there’s been a general drift to it getting drier” in California, and in the Colorado River Basin.
There is still considerable uncertainty in climate and water projections, and the Colorado River serves as an outsized example of the challenges facing researchers and water managers. Denver Water supplies 1.2 million people and gets about half of its water from the Colorado River. “The question is, does Denver have to recalculate what the firm annual yield of our water rights is because of global warming?” says Chips Barry, Denver Water’s manager. “And the answer is, maybe. How do you do that? The answer is, I haven’t got the foggiest idea, because you can assume things all over the map.”
Climate scientists are working to puzzle out the reasons behind the sometimes-contradictory projections generated by what they call “dueling models.” Temperatures are incontrovertibly rising. Less clear is how temperature will affect precipitation, how evaporation will affect runoff, and how both factors will affect the total volume of river water that can, in turn, be stored behind dams. And on the Colorado River, where future projections are especially bleak, “the question that’s out there,” says Dettinger, “is, ‘Is that going to be a large reduction in runoff, or a less-large reduction in runoff?’ ”
Marty Hoerling, a Boulder, Colo.-based meteorologist for the National Oceanic and Atmospheric Administration, has projected that, because rising temperatures and increasing evaporation will reduce runoff, the average annual flow in the Colorado River over the next quarter century may be just 10 million acre-feet. That is the same amount of water that was in the Colorado during the four worst years of the current drought. It left existing reservoirs half empty; more alarming, it is a third less than the amount of water that is already being used every year.
A recent paper by Niklas Christensen and Dennis Lettenmaier, at the University of Washington, projects more modest decreases in flow. But the disparities between various projections leave water managers without a good sense of just how bad a scenario to prepare for. “We bring in these climate scenarios and say, ‘Gee, you should do this and you should do that,’ ” says Lettenmaier. “(Water managers) look at it and say, ‘Five years ago, there was this scenario, and now there’s a different one.’ We’re all over the map.”
In the absence of a more precise view of the future, some municipal water managers are trying to maximize the flexibility in their existing systems. Marc Waage, the water resources director for Denver Water, says the agency is focused on “ ‘no-regrets’ planning, where you take incremental steps that work well in a variety of different future scenarios, even though you don’t know which one of those scenarios is going to happen.” That strategy aims to create a diverse portfolio that includes existing reservoirs, increased water recycling, and water-efficiency improvements. That, says Waage, “will tend to work well under a number of different scenarios, so it makes sense to continue until we know more.”
The Metropolitan Water District of Southern California supplies water to 18 million people in Los Angeles and San Diego. Roger Patterson, an assistant general manager for the district, says that although Metropolitan hasn’t ruled out the possibility of considering new dams, “people are trying to get the most out of the infrastructure we’ve already put in place.” Metropolitan has already been doing that by leasing water from farmers to supplement its own supplies. Farms use about 80 percent of the water in the West, and water transfers, says Patterson, are “a prime mechanism” for helping cities get through droughts. He says that building additional canals, to more tightly link the various water systems in California, could help expand the range of possibilities for transferring water from farms to cities.
Farms in the crosshairs
But an increased reliance on water transfers puts the squeeze on the region’s farmers. And that, more than anything else, may be driving the push for more dams — which could provide an alternative supply for cities and take the heat off farms. The dam bill in California “is really about providing enough (water) so the water currently being used by the ag community is not at further risk of either being severely reduced or eliminated altogether,” says Sen. Cogdill. “The costs being projected right now range from $325 to $350 per acre-foot. Given the fact that most of the ag community in this state relies on water that’s considerably cheaper than that, you’re probably going to be seeing more of this water allocated for urban municipal uses and for environmental benefits.”
Cities, however, will be looking closely at cost and — now, more than ever — reliability. Farmers will be increasingly plagued by the fact that they get their water at such low prices. Urban water agencies have been regularly leasing water from farmers for considerably less than $325 an acre-foot, and it will take a lot to convince an urban water manager to buy into a dam whose supplies are both more expensive, and less reliable, than water that can be bought off the farm.
The same pressure is building in Colorado, where the agencies that supply Denver’s growing suburbs are increasingly reliant on buying farm water. “The people and water supplies in our district are in the crosshairs,” says Eric Wilkinson, the general manager of the Northern Colorado Water Conservancy District, a major irrigation district north of Denver. “Irrigated agriculture within our district is basically the supply of choice for growing municipalities.” Last year, the district proposed that Denver’s suburbs build a new $4 billion reservoir on the Yampa River — a tributary of the Colorado.
That might buy some breathing room for farmers, but with projections of lowered Colorado River flows in the future, it could be a losing bet for everyone at the table. Eric Kuhn, the general manager of the Colorado River Water Conservation District in Glenwood Springs, Colo., has closely followed the evolving climate science. “All of the studies (for the Colorado River) point the same direction, which is less water and less flow,” he says. “Why would you build more dams when the existing dams don’t fill?”
The author is the West Coast correspondent for High Country News.
This article was made possible with support from the William C. Kenney Watershed Protection Foundation and the Jay Kenney Foundation.