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January 16, 2024  |  Written by Ryan J. Mitchell

Understanding Calls in Colorado and Avoiding Water Cuts in a Year of Drought

“First in time, first in right” is the old adage underpinning the prior appropriations doctrine. Stated more fully, a person that diverts water from a stream and applies it to a beneficial use has a priority to use that water over any other person that accomplishes the same at a later point in time. Such priority applies to the entire length of the stream—whether a water user is at the head of the stream or its end.

Under Colorado water law, when there is insufficient water to satisfy a senior user’s rights, a call is placed on the stream to restrict junior diversions. Such a call requires all upstream users with a junior priority to cease diverting water until the calling user can divert its full amount. Notably, as climate change results in winter warming faster than the other seasons, below-average snowpacks are becoming the norm, and calls are becoming more frequent. Some calls are even applying to relatively senior water rights for the first time since being decreed. Resultingly, senior water users in Colorado need to consider obtaining a plan for augmentation—one of the few options that allow a water user to continue diverting during a call.

Last year, water users placed significantly fewer calls on streams because of historically large snowpacks. Mountains act as natural reservoirs by collecting snow in the winter and releasing water in the spring as temperatures increase. These snowpacks are a critical component of water supplies across the west, making up about 60% to 70% of the water supply. But this winter is shaping up to be a different story—mild temperatures and below-average precipitation thus far have begun to trigger the snowpack alarms.

In the water management context, the standard measurement used to determine the size of an area’s snowpack is called the Snow Water Equivalent (SWE). This method is used because the water composition of snow can vary dramatically based on temperature at the time of a snowstorm. Thus, different storms bring different types of snow that can hold different amounts of water. For example, for every one inch of precipitation as rain, warmer-weather snowstorms can create two inches of sleet, and very cold snowstorms can create over 50 inches of very dry, powdery snow. Because of this variability, snow depth does not translate directly to the amount of water held in a snowpack.

The following two graphics depict the current state of western snowpacks by SWE. This map shows the current SWE of each individual basins as a percentage of that basin’s median SWE from 1991-2020. Across the board, almost all basins are below their 1991-2020 median. For example, the current SWE for the Colorado Headwaters basin in Colorado is 78% of its 1991-2020 median. At this same time one year ago, the Colorado Headwaters basin was 132% of its 1991-2020 median.

This next graph plots Colorado’s 2024 SWE as compared to its historic maximum, historic minimum, and 1991-2020 median. Colorado’s current SWE is roughly 74% of the 1991-2020 median, putting it in the 16th percentile of its historic records.

While the remainder of this winter season could see an abundance of snowfall, there remain few historic examples of the SWE reaching or exceeding the average peak (identified by the green x in the above graph) when starting at such a low point. Thus, Colorado will likely see an increase in the frequency of calls during 2024.

To proactively protect water supplies in response to a call, water users should consider obtaining court-approved plan for augmentation under the 1969 Water Rights Determination and Administration Act. In general, a plan for augmentation involves the upstream storage of water and accounting that tracks stream flows and determines when the stored water should be released to mitigate injury to downstream senior water users. Under an augmentation plan, a junior user can continue to divert water during times of low stream flows because the stored water is released to satisfy a senior user and prevent curtailment of the junior user.

For more information or questions on Colorado plans for augmentation or other short-term options, please contact:

Somach Simmons & Dunn provides the information in its Environmental Law & Policy Alerts and on its website for informational purposes only. This general information is not a substitute for legal advice, and users should consult with legal counsel for specific advice. In addition, using this information or sending electronic mail to Somach Simmons & Dunn or its attorneys does not create an attorney-client relationship with Somach Simmons & Dunn.


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