@ColoradoClimate: Weekly Climate, Water and #Drought Assessment of the Intermountain West

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Western states buy time with a 7-year #ColoradoRiver #drought plan, but face a hotter, drier future — The Conversation #DCP #COriver #aridification

The white “bathtub ring” around Arizona’s Lake Mead (shown on May 31, 2018), which indicates falling water levels, is about 140 feet high. AP Photo/Ross D. Franklin via The Conversation

From The Conversation (Brad Udall, Douglas Kenney, John Fleck):

As Midwest states struggled with record spring flooding this year, the Southwest was wrestling with the opposite problem: not enough water. On May 20, 2019, federal officials and leaders from seven states signed the Colorado River Drought Contingency Plan, a sweeping new water management agreement for this arid region.

The plan is historic: It acknowledges that southwestern states need to make deep water use reductions – including a large share from agriculture, which uses over 70% of the supply – to prevent Colorado River reservoirs from declining to critically low levels.

But it also has serious shortcomings. It runs for less than a decade, through 2026. And its name – “Drought Contingency Plan” – suggests a response to a temporary problem.

As scholars who have spent years researching water issues in the West, we know the Colorado River’s problems are anything but temporary. Its waters have already been over-allocated, based on a century of false optimism about available supply. In other words, states have been allowed to take out more than nature puts back in.

Now the river is being further depleted by climate change-driven aridification. The next steps, post-2026, require a recognition that Arizona, Nevada and California will likely have to come to terms with permanent reductions in their Colorado River supply. For their part, Wyoming, Utah, Colorado and New Mexico must abandon dreams of taking ever-larger gulps from the Colorado River to support future growth.

The Colorado River is about 1,400 miles long and flows through seven U.S. states and into Mexico. The Upper Colorado River Basin supplies approximately 90 percent of the water for the entire basin. It originates as rain and snow in the Rocky and Wasatch mountains. Credit USGS.

Draining western reservoirs

The Drought Contingency Plan is an important step in that direction. By creating a new layer of rules that temporarily reduces water allocations, it significantly reduces the chance of emptying Lake Mead, the massive reservoir on the Arizona-Nevada border that supports residents of Arizona, Nevada, California and Mexico. Without the plan, the lake conceivably could have been sucked dry – a devastating prospect for 40 million people who live in the Colorado River Basin.

As a seven-year stopgap, the plan comes just in time. After 19 years of unprecedented low flows, the nation’s two largest reservoirs – Lakes Mead and Powell – collectively contain only 40% as much water as they held in 2000. And while the winter of 2018-2019 was a big snow year, it merely balances the previous year, when record-setting warm and dry weather in large parts of the basin lowered water levels in Lake Powell by over 40 feet.

Dry years like 2018 are the far more likely future. From 2000 through 2004, annual runoff totaled only 65% of the 20th-century average. And in 2012-2013, it was just 60% of the 20th century average. More episodes like these would seriously compromise the system’s ability to provide water to the seven Colorado River Basin states and Mexico.

A hotter, drier future

Climate change is and will remain a significant issue. Since 2000, Colorado river flows have been 16% below the 20th-century average. Temperatures across the Colorado River Basin are now over 2 degrees Fahrenheit warmer than the 20th-century average, and are certain to continue rising.

Scientists have begun using the term “aridification” to describe the hotter, drier climate in the basin, rather than “drought,” which implies a temporary condition.

Studies show that higher 21st-century temperatures have been reducing runoff. Warmer temperatures increase evaporation from soils and water bodies, and increase sublimation from snowpacks – direct conversion of snow and ice into fog or steam, without melting first. And they increase plant water use, due to a longer growing season and more warmth on any given day.

In a 2017 study, one of us (Brad Udall) and Jonathan Overpeck found that higher temperatures due to climate change had reduced the flow of the Colorado River by approximately 6%. The study projected that additional warming could reduce flows by approximately 20% in 2050 and up to 35% by 2100 if precipitation levels did not change. A 2018 modeling study estimated the flow losses due to higher temperatures at about 10%.

Overuse in the Lower Basin states of Arizona, Nevada and California is the second major problem. This problem is officially known as the “Structural Deficit” – a 1.2 million acre-foot gap, representing 8% of the river’s flow, between allocations made in the early 20th century and the amount of water the river can provide.

Cities from Las Vegas on the north to Tucson and Phoenix on the south and west to San Diego and Los Angeles all have come to depend on that water. Meanwhile, agriculture – including important areas like Yuma and the Imperial Valley, where much of the nation’s valuable winter produce is grown – uses 70% of the river’s water.

The All American Canal diverts water from the Lower Colorado River to irrigate crops in California’s Imperial Valley and supply 9 cities. Graphic credit: USGS

Looking past 2026

With the contingency plan only running until 2026, Basin leaders are already discussing the framework of a new planning effort. In our view, the process should be open and inclusive, given the huge number of competing interests in the region, including municipalities, agriculture, tribes and the environment.

An effective long-term plan should solve the overuse problem in the Lower Basin, while preparing for extended and unprecedented low flows. It should revisit a number of long-standing assumptions about how the river is managed, including the Upper Basin’s so-called “delivery obligation” to the Lower Basin, which leaves the upper states – Wyoming, Utah, Colorado and New Mexico – bearing the burden of climate change, while the Lower Basin states remain free to overuse. And it will have to address the reality that there is not enough water for users in the Upper Basin to continue exporting ever more water to growing cities like St. George, Utah, and Colorado’s Front Range.

Solving the twin problems of climate change and overuse will not be easy. The good news is that water users in the basin have found ways to work together for everyone’s benefit, first in a set of water management guidelines negotiated in 2007, and then with the Drought Contingency Plan.

Now, after staving off worry that system reservoirs could drop to calamitous levels, water users and managers can focus on these pressing longer-term issues. It is time to step back, look at the big picture and design a water management system that works for all stakeholders in the basin for the next several decades.

Brad Udall, Senior Research Scientist, Colorado Water Institute, Colorado State University; Douglas Kenney, Senior Research Associate and Director, Western Water Policy Program, University of Colorado, and John Fleck, Professor of Practice in Water Policy and Governance and Director, Water Resources Program, University of New Mexico

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Moffat Collection System Project update: “Our problem is rooted in demand and resiliency” — Jeff Martin

Gross Reservoir , in Boulder County, holds water diverted from the headwaters of the Colorado River on the West Slope. The reservoir is part of Denver Water’s storage system. Photo: Brent Gardner-Smith/Aspen Journalism

From The Colorado Sun (Amanda K. Clark):

Raising the 55-year-old dam near Boulder is essential to keep a stable water supply in a changing climate, utility says. Residents insist conservation could be just as effective.

Denver Water — Colorado’s largest and oldest utility company — in July 2017 received one of the final permits needed to raise Gross Reservoir Dam by 131 feet to increase water storage capacity by 77,000 acre-feet, or an additional 25 billion gallons of Western Slope water…

The expansion, in the works for more than a decade, is part of the company’s long-term plan to help meet increasing water demands along the Front Range and buffer customers from future water-supply variability due to climate change…

Denver Water has been met with sustained opposition from Boulder County residents and a handful of environmental groups who say the utility can address its water needs through expanded water conservation efforts on the Front Range.

But with Colorado’s population growth showing no signs of slowing, water conservation may be inadequate to address projected shortages in the coming decades.

Other concerns raised by opponents include sustained disruption to surrounding residents, increased traffic, health concerns and environmental impacts to fish and wildlife.

Gross Reservoir is filled primarily from snowmelt that flows from the Fraser River, a tributary of the Colorado River. The water is transported underground from west of the Continental Divide to the east by a pipeline called the Moffat Water Tunnel.

The controversy over the Gross Reservoir expansion, estimated to cost $464 million, echoes an all-too-familiar story: a highly contentious discussion of tradeoffs that has rippled across the Western United States for decades.

As cities and states across the West grapple with swelling population alongside diminishing water supplies as a result of climate change, water-resource agencies such as Denver Water are faced with the delicate task of balancing the health of ecosystems with municipal, agricultural and recreational needs…

Jeff Martin, Denver Water’s project manager for the expansion project, doesn’t skirt around the controversy. He recognizes that the project is going to cause disruption and says that Denver Water has worked with the residents to find ways to minimize the project’s impact.

“This has been a process,” Martin said. “We started in 2004, it took 13 years to move through the environmental assessment and permitting process. And we’ve made a lot of changes and adjustments to our plans since the beginning.”

“No single solution is out there,” he said. “Our problem is rooted in demand and resiliency, and what I mean by resilience is that we have to make sure we have the water when we need it, and where.”

[…]

For Patty Limerick, director of the CU Boulder’s Center for the American West and former Colorado Historian, you can’t talk about water issues on the Front Range without first looking back in time.

When early white explorers arrived here, they deemed the Front Range unfit for settlement due to lack of water. Today, 1.4 million Denver residents have access to clean drinking water due in large part to Denver Water’s enormous infrastructure web that diverts water from the South Platte, Blue, Williams Fork and Fraser river watersheds to be stored in a network of reservoirs spread over eight counties, including Dillon, Strontia Springs and Cheesman.

“One thing that I find fascinating, and is important to talk about, is the incredible amount of engineering that had to occur to make any of this possible in the first place,” Limerick said.

“We, as a society, have to recognize the improbable comfort that was made possible by a taken-for-granted, but truly astonishing, water infrastructure that was put in place a hundred years ago.”

[…]

“The year 2018 was very similar to what we would expect to see under a climate change regime. And that was a very intense but short-term drought,” said Taryn Finnessey, senior climate change specialist with the Colorado Water Conservation Board.

“We saw some reservoirs in the state declined by 50 percent in a three- to four-month period. So that obviously could not be sustained multiple years in a row,” she said. “Water providers are increasingly integrating climate change models into their water supply projections. They know that what we’ve seen in the past might not fully represent what we might see in the future. Denver Water is one of the more advanced utilities when it comes to this.”

Finnessey says it’s not just about how much precipitation falls from year to year. It also has a lot to do with increasing temperatures, contributing to the long-term drying out of the West, a phenomenon scientists are referring to as aridification. As temperatures rise, more moisture is sucked up by the atmosphere through evapotranspiration, leaving less viable water for humans-use in the system.

“We are planning for infrastructure that will be built in the next 20 years, that is supposed to last for the following 100 years,” said Reagan Waskom, director of Colorado State University’s Colorado Water Institute. “Our world is changing significantly faster than that. And not in a linear way. How do we adapt to that?

“Water managers have to plan for extremes,” he added. “A year like this year is an argument for reservoirs. Even with climate change, you’re still gonna have some good years. And we need to be able to capture it and save it for the bad years, whether that’s in underground aquifers or in reservoirs.”

Denver Water’s collection system via the USACE EIS