Why can’t we make more snow to fill the Colorado River’s big reservoirs?
By Allen Best
After a so-so winter, the snow piled up through May in the mountains of Colorado, taking the edge off drought. This takes the edge off of the big Colorado River reservoirs, Lake Mead and Lake Powell. But the overarching story at those reservoirs since 1999 has been of decline, even after a few big years.
In the last several years, there has been increasing talk about the potential for the two reservoirs to become empty. Las Vegas, reliant upon Lake Mead for most of its water, isn’t just talking about the possibility. It is nigh-on to completing a third tunnel into the reservoir, this one at a cost of $817 million and, unlike the others, at the very bottom of the reservoir, in case there’s nothing left of Lake Mead except for the Colorado River. That’s how dire Las Vegas, operating as the Southern Nevada Water Authority, takes this potential of long-term drought.
Eric Kuhn, the manager of the Colorado River Water Conservation District, spoke to the implications of this continuing drought at a forum in Colorado’s Summit County this spring. “Bad things happen when Lake Mead and Lake Powell get drained,” he said in an event covered by the Summit Daily News. He described the draining of Lake Mead as a distinct possibility in the next few years.
What about building a pipeline to the Mississippi River or some other water-rich location? “To expect that we can export our problems to somebody else, I just don’t see that somebody else will willingly accept them,” he said.
How about just making some more water? That effort began soon after World War II in different times of drought. Scientists at General Electric in New York state had discovered the general principle. And in some places of the West, cloud-seeding has occurred since the 1950s – including, at Vail Mountain, since 1978.
But does it work? Since the federal government yanked research dollars from cloud-seeding experiments in the 1980s, relatively little rigorous science had been conducted. Instead, there were the claims of commercial-cloud seeders, who predicted gains of 10 to 15 percent—as long as they had clouds to work with.
In 2004, Wyoming set out to fill that gap. An experiment that ultimately cost $14 million was designed by scientists working for a federal laboratory, the National Center for Atmospheric Research. Parallel mountain ranges southwest of Laramie, just north of the Colorado border, constituted the Wyoming laboratory. Propane was burned to loft silver iodide from ground-based generators into the clouds passing over the Sierra Nevada and Medicine Bow ranges. In the experiment, 154 storms during six winters had the temperatures needed for effective seeding, but only 118 had the moisture content. And of those, 18 were tossed out because of contamination problems.
Slim statistical evidence
Last December, at a meeting room in Cheyenne, scientists delivered the results. It took a full afternoon and the results were sometimes confusing. But hydrologists and meteorologists who listened to the proceedings remotely told me they had no trouble hearing the key statistics: just a 3 percent increase in precipitation but with the 28 percent probability that cloud-seeding had nothing to do with the increase. Only by creating models were researchers able to make a case that snowfall had been augmented 5 to 15 percent.
Taking stock of this and other winter weather-modification studies, the Bureau of Reclamation was unimpressed. “As such,” said the agency in a draft analysis released in February, “the ‘proof’ the scientific community has been seeking for many decades is still not in hand.”
Proof in science requires a 95 percent probability of causality. This is extremely difficult to achieve in complex atmospheric processes, whether cloud-seeding or many of the processes involved with a warming global climate.
In Wyoming, elected officials have decided the evidence to support cloud-seeding is strong enough to justify additional investments in various drainages—including the Wind River Range, which produces water for a tributary of the Colorado River—even as they have been loathe to admit the science of global warming.
Wyoming isn’t alone. Water agencies and cities from Denver to Los Angeles pay for seeding clouds in the mountains of Colorado and Wyoming, and representatives heard what they wanted to hear.
“It’s good evidence that it works,” said David Cole, who administers weather-modification programs for the Utah Division of Water Resources.
“There is always that question, ‘Can you prove it beyond a shadow of a doubt?’” he added.
From Los Angeles comes a similar appraisal of confirmation. “These results are consistent with historic studies,” said Tom Ryan, of Metropolitan Water District of Southern California, a consortium of agencies that collectively serves 18 million people.
I heard similar remarks from the Central Arizona Project, which uses a 336-mile-long system of aqueducts, tunnels, pumping plants, and pipelines to deliver water to Phoenix, Tucson, and cotton farms and golf courses along the way.
Along with Las Vegas, Arizona and California chip in to pay for cloud-seeding in Colorado and Wyoming.
Dan Breed, project scientist with NCAR, said that failing to achieve a 95 percent confidence level in results is not unusual in cloud-seeding studies. The fundamental problem, he says, is the complexity of atmospheric processes.
It’s the same challenge that has prevented most climate scientists from linking specific weather events, such as the September 2013 floods in Colorado, to rising global temperatures and the 3 to 5 percent observed increase in atmospheric moisture related to that warming.
“When it comes to the atmosphere, there are just too many variables, and that variability just keeps rearing its ugly head when it comes to cloud-seeding,” says Breed. “Even in this case, where we tried to make things as homogeneous as possible to reduce that variability, variability still kind of hurt us.”
Breed thinks research might better be invested in understanding specific atmospheric processes of wind, temperature, and precipitation. For example, how likely is it that silver iodide or other seeding agents released from the ground will get into the clouds?
Understandings of atmospheric processes, says Breed, has mostly come from observations, instead of experiments – because of that same variability.
This lack of certainty does not necessarily kill the prospects of cloud-seeding, as is demonstrated by the continued interest of Wyoming legislators in funding cloud-seeding.
Cloud-seeding to the rescue?
Can cloud-seeding the answer to the problems of California, now in its fourth year of drought, or of the Colorado River?
The river is notoriously strapped to meet all of the wants and maybe even the needs. River flows have declined 20 percent in the 21st century as compared to the last century.
Breed disputes conclusions that cloud-seeding doesn’t necessarily work. But he doesn’t see it as a game-changer for the Colorado River. Modifying the weather is a fairly straightforward, quick and inexpensive way to produce more water, but the gains are marginal. “It is not, he says, a magic bullet. “It won’t solve the problem.”
In his appearance in Summit County, Kuhn took a broad view, describing the 21st century as a time of transition. “After 100 years of develop more, develop more, develop more, we’re going to have to cut back our uses.”
That’s the difficult conversation now underway in California as residents in places like San Jose argue about lawn sizes and almond groves. It’s also the more earnest conversation that, despite the extraordinary rains in May, is getting underway in Colorado.