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.”

Plan B

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.