The Colorado River and reckoning time for the Front Range

Dissonance exists between life-close-to-normal policies regarding urban water use and the growing crisis on the river

by Allen Best

Casually surveying the urban landscapes in much of Colorado’s Front Range, you’d never know that the Colorado River — the source for roughly half the water of the cities — has deteriorated to its most pitiful shape of perhaps the last century.

Oh, yes, some utilities — notably Denver Water and Aurora Water, which together serve 1.9 million residents — have imposed rigorous stage-one drought watering restrictions. Outdoor irrigation is allowed twice per week and never during the heat of day. Other water utilities that tap Colorado River water, however, have asked only for voluntary cutbacks, if any at all.

Jeff Lukas, a water consultant with several decades invested in climate change work, says this seeming aloofness of some cities will not persist indefinitely. That is certainly true if the record heat and abnormal dryness of the past winter continues into 2027. They may have no choice.

“I think Front Range cities will be asked, whether nicely or not, to reduce their Colorado River diversions,” said Lukas in a May 11 webinar. “The mechanism for that is unclear, but I think it’s going to happen.”

Water rights of the Front Range cities — and many of those on the Western Slope, too — are junior to the Colorado River Compact. It was negotiated in 1922, making diversions more recent than that junior.

Problems in the basin were becoming apparent in the 1990s. The warming climate in this century has provoked changes. By all accounts, they have not been enough.

Lukas, as a dendrochronologist at the Institute of Alpine and Arctic Research in Boulder 20 years ago, was teasing out evidence from tree rings to understand the climates of the Colorado River Basin during the last 1,200 years.

Later, as a scientist with the Western Water Assessment, Lukas co-authored (with Liz Peyton) a 2020 report called Colorado River Basin Climate and Hydrology: State of the Science. That 500-page report integrated more than 800peer-reviewed studies to help water managers understand physical processes, climate risks, and forecasting tools across the basin.

In 2024, with the state climatologist, Russ Schumacher, and several others, Lukas turned out the 100-page volume called “Climate Change in Colorado.”

Based in Lafayette, Lukas now works as a consultant. At Lukas Climate Research and Consulting, he specializes in the overlapping areas of climate hazards, water resources, and ecosystems.

Lukas, in a presentation he titled “Running dry on the Colorado River: The roots of the crisis & its implications for the Front Range,” explained the big picture and Colorado’s Front Range part in it.

Defined by the Continental Divide, Colorado has an inverse relationship between its eastern and western slopes. About 90% of the state’s residents live to the east, nearly all at the foot of the Rocky Mountains, whereas 80% of the state’s precipitation originates on the west side, in the headwaters of the Colorado River and its tributaries.

Snow from the Gore Range and other “islands” of precipitation in Colorado provide 50% to 60% of the water in the Colorado River.

Colorado itself provides 50% to 60% of the water in the entire Colorado River, depending upon the year. This year has been a terrible year everywhere in the basin, Colorado included.

Lukas explained that “islands of moisture” provide nearly all the water in this 244,000-square-mile basin. The high mountains constitute these islands. Some places deliver more than others. Buffalo Pass, near Steamboat, famously has had prodigious volumes of snow. This snow, when melted, can produce 50 inches of water.

It takes 20 inches or more of precipitation in these mountain islands to produce meaningful runoff. Even then, it doesn’t all end up in the Colorado River. In Colorado and the three upper-basin states, he said, 16% of the rain and snow that falls becomes water in the Colorado River. In the hotter lower basin, the figure is 3%.

“The atmosphere takes back most of what it giveth, even in the wetter upper basin,” he said.

Evaporation and transpiration are the pickpockets of this water. Heat produces evaporation, and we’ve had plenty of that this year.

Temperatures during November through April were the warmest on record in Colorado for that span of months. March heat was exceptional. This produced runoff in the rivers that in most cases may surpass that of May or June, the traditional times for peak runoff. Peak runoff has been trending earlier by several weeks during the last few decades, but this was a leap of about two months.

Runoff for April through July — a time that normally accounts for 70% to 80% of annual streamflows — this year will likely deliver no better than 20% to 40%. In its May report, the Bureau of Reclamation said April flows into Lake Powell were 40% of the average during the last 30 years and it expects flows in May to sink to 9% of that average.

Can it get any worse? Count on it, said Lukas.

“We should expect not every year to look like 2026 from here on out, but more years in the future will look like 2026. And somewhere down the pipe, not as far in the future as we would like, there will be a year worse than 2026 for the Colorado River.”

This is so very different from what was assumed by the delegates from the seven basin states who gathered in 1922 in Santa Fe to apportion the Colorado River.

The role of reservoirs

Taking the big, long-term view, Lukas pointed out that the overall story of the Colorado River is one of modifications needed to suit human uses. “It’s all about smoothing out the natural variability in the availability of water over space and over time.”

Reservoirs are the primary means by which humans have been able to “smooth out the natural variability.”

The Colorado River Basin has 60 million acre-feet of storage. That’s four times the annual flow. Five-sixths of the storage capacity is found in the desert in two vessels: lakes Mead and Powell. The headwaters have many reservoirs but they are relatively small. The total storage capacity is 2,000 times more than the volume of Dillon Reservoir.

Since 2000, stored water in those two big buckets, Mead and Powell, has declined from 49 million acre-feet to 16 million acre-feet as of May. Of that, 9 million lies at elevations below the lowest outlets. These are called dead pools.

Powell had declined to about 24% of its capacity in May 2022 when this photo was taken. It rebounded somewhat with the next winter, but has once again declined to 24.5% of capacity on Memorial Day this year and will almost certainly fall lower.

Those delegates in 1922 who crafted the Colorado River Compact, the legal document that provided the basis for nearly all these dams and aqueducts subsequently built, assumed annual flows of 17 million to 18 million acre-feet. They were overly optimistic. The 20^th century average was 15.2 million acre-feet.

Now comes the 21^st century, and the average at Lee Ferry has dipped to 12.2 million acre-feet. This has implications for the Front Range cities but also farms. If Colorado must reduce its diversions to accord with the compact, those rights dated before 1922 will be exempt from reductions. The giant transmountain diversions have come more recently, as have many of the diversions for towns and cities on the Western Slope.

Accumulating evidence fingers human-caused climate change with large amounts of responsibility for declined flows. Lukas said his rule of thumb is that the role of greenhouse gases overall are responsible for two-thirds of lower flows.

As for the mechanics of this shift, rising heat is one important “knob,” said Lukas. As the atmosphere warms, it reduces “runoff efficiency” even more, sending water into the atmosphere instead of into streams and then rivers. Accumulating evidence fingers human-caused climate change with responsibility for most and possibly all of increased temperatures.

Precipitation has declined about 5% since 2000, with a larger reduction in spring, an important time of year to get moisture. Here, the link to the warming climate is less clear. “It seems increasingly likely that climate change is changing the dynamics of storm tracks and the persistence of, say, high-pressure systems over the interior West,” said Lukas. “That is, at least in part, responsible for why we’ve had less precipitation since 2000.”

The Colorado River, though, had problems even before the warming climate began throwing sharp elbows in water volumes. The reservoirs of the Colorado River Basin were 92% full in 1999, a wet decade overall. Even then, however, the Colorado River had ceased to reach the Pacific Ocean. There were too many straws inserted.

Less than 12% of the river’s flow goes to urbanized and industrial uses. Lukas pointed out that cities have become more efficient in their use of water. The rule of thumb for Denver and other Western cities is that one acre-feet of water meets the needs of a three households on an annual basis. That compares with two households a few decades ago.

Mining of fossil fuels and minerals uses a small amount. Evaporation from reservoirs and rivers and other “system losses” accounts for about 15%.

That takes us to agriculture. It uses 75% of the river’s water in the Colorado River for irrigation on 5 million acres. Some of that land lies outside the basin itself. That includes the South Platte and Arkansas River valleys of eastern Colorado.

Over half of that water — about 9 million acre-feet — gets used to grow feed for livestock, mainly alfalfa and pasture grass.

Might cities want to cut deals with farmers to “share” the water? This discussion has been underway for at least 15 to 20 years. Some pilot projects in Colorado and elsewhere have been launched to see what this might look like. A strong proponent has been James Eklund, a water attorney in Denver. Others question how this is done and, for that matter, whether we want to do it. But certainly, water for urban uses has higher monetary value than growing hay to feed cattle.

Why the restraint of cities?

As for the Front Range cities, the big question is whether they are planning for a river that produces even less than it does now.

In 2024, Andy Mueller, the general manager of the Colorado River Water Conservation District, suggested the need to start planning for a river that may deliver less than 10 million acre-feet in coming decades. Some thought then that the state engineer, Jason Ullman, needed to start sorting through this matter of junior vs. senior rights. Jim Lochhead, a former water attorney on the Western Slope and later CEO of Denver Water, pushed back, saying it was premature given the huge amount of work that would be required. See: “Heading for the Colorado River Cliff,” Big Pivots, Oct. 20, 2024.

At the Zoom session on May 11, I asked Lukas about the modest watering restrictions by Front Range water providers. He had previously described mixed signals from the water utilities. If 2027 is dry again, expect more uniformity around drought restrictions. “But it’s pretty weird right now,” he said.

With the attention to the Colorado River in the news media, it seemed like a perfect opportunity for the water utilities to mount more aggressive campaigns. Any idea why they had not, I wondered.

The utilities, he said, are reluctant to deliver regulations that produce discomfort around outdoor water-use restrictions. They don’t want to do this unless absolutely necessary.

Part of this is because of experiences during the covid epidemic. A lesson to public servants during that time made them more reluctant to push the public to do things they don’t want to do. “You only want to exercise that authority, that public legal authority, sparingly and only when it’s clear that is what is really necessary.”

Revenue was another consideration. Water infrastructure is expensive, and the money to pay for it comes from charges for water use. By imposing limits, you reduce revenue and hence must charge more for water. The conundrum is that reducing use doesn’t necessarily mean you pay less. In some cases, less water may require more infrastructure. This is a hard message to convey.

“What you’re seeing is a dissonance between the circumstances and what’s happening, at least this year,” he said.

Or at least right now. We have had rainy weather in May. Some meteorologists think we may end up with healthy rainfall this summer. If instead the summer is like the winter, very hot and dry, I expect the utilities might pick up their game.

Jeff Lukas presented in a session called Zoom at Noon. You can see the hour-long presentation here. The passcode is %ACg9*XU