Planning for drought, or planning for a drier future?
April 14, 2018
Looking up at the Grand Mesa from Grand Junction in early April, it's good to see snow on its flanks. For too much of this past winter, they have been bare. Skiers felt the pain of the dry winter early; fish and ranchers will feel it this summer.
In Grand Junction, the impacts of this year's drought will likely be eased by last year's bounty, stored in reservoirs upstream. More troubling is the trend we've been seeing since 2000, which scientists are warning could signal a shift to a more arid climate.
Since 2000, we've had a lot more dry years than wet years in the Colorado River Basin. In a report released in March, the Colorado River Research Group warns that it may be more accurate to see this succession of dry years as a process of aridification, rather than a drought: we shouldn't assume that it will end any time soon.
The group points to several recent studies showing that warmer temperatures have already led to a larger portion of our snowpack evaporating or getting taken up by plants before it has a chance to reach streams. 2017 was a case in point, with a very large snowpack converted into only moderately above-average inflows into Lake Powell.
Water managers and policymakers have not failed to notice this drying trend, reflected most obviously in dropping levels in Lakes Powell and Mead. Water users in the lower basin states of Arizona, California and Nevada have reigned in their water use a bit, managing to keep Lake Mead just barely above official shortage levels for the past few years. In the upper basin states of Wyoming, Utah, New Mexico and Colorado, water leaders have been conducting modeling exercises to assess the risk of critical shortages and experiments to test options for responding.
The Colorado River Risk Study, spearheaded by the Colorado River District and the Southwestern Water Conservation District, has modeled several hydrology and water demand scenarios to assess the risk of Lake Powell dropping too low to reliably generate hydropower (somewhere between elevations of 3,490 and 3,525 feet above sea level). If Powell drops much further, it could also become difficult to release enough water through the dam to meet downstream obligations under the 1922 Colorado River Compact. If that happens, cities could rush to purchase water rights from farms, potentially drying up much of the agriculture on the Western Slope.
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Using historical hydrology from 1988–2012 and demand numbers that roughly track current use trends, modeling indicates a 20 percent chance of Powell dropping to elevation 3,525 between now and 2036 if we don't significantly change how water is managed. Using the same demand and hydrology data, that risk could be cut in half if major reservoirs like Blue Mesa and Flaming Gorge release extra water to Powell, and the lower basin states implement their own plans to protect Lake Mead water levels. The risk drops further if conservation activities generate water that can be stored in a "bank" and released as needed. However, major benefits would come only after such a bank has had time to accumulate a significant amount of water.
Meanwhile, the Upper Colorado River Commission has been giving out grants to test whether paying willing water users to temporarily reduce their use could help boost water levels in Powell. Such temporary reductions, rotated between different water users, are seen as an alternative to the permanent "buy and dry" of agricultural water rights.
Participants in the grant program include the Grand Valley Water Users Association, which chose several farmers by lottery to temporarily fallow their land in exchange for payment, and farmers in the North Fork and Uncompahgre Valleys who reduced irrigation or grew alternative crops under the program.
The Commission's report on the program concluded that it could work, but several hurdles would have to be overcome. For example, it is unclear if sufficient legal tools currently exist to ensure that water conserved by one user could make it to Lake Powell without being picked up by someone else along the way. Measuring the amount of water saved through modified irrigation practices is also technically challenging. And the cost could be high — at the rates used by the program in 2017, it would cost $40 million to conserve about 200,000 acre feet of water.
As drought planning has been discussed at Western Slope water meetings, concerns have been raised about how to ensure fairness, with a strong desire to ensure that cities share the pain of any use cuts with farmers. There is also concern that proactive conservation could simply facilitate new drains on the Colorado River system, rather than protect existing users from drier conditions.
The data clearly demonstrate that we face the risk of a drier future, in which past ways of managing water will not continue to be viable. There are ways to mitigate the impact on our communities, but they are likely to be expensive and will certainly be complicated. This makes it all the more important to press forward now. The sooner we can find equitable, feasible mechanisms for adapting to drier conditions, the more smoothly we will be able to handle both temporary droughts and drier conditions over the long term.
Hannah Holm coordinates the Hutchins Water Center at Colorado Mesa University, which promotes research, education and dialogue to address the water issues facing the Upper Colorado River Basin. Support for Hutchins Water Center articles is provided by a grant from the Walton Family Foundation. You can learn more about the center at http://www.coloradomesa.edu/water-center.
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