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Depleted by Drought, Lakes Powell and Mead Were Doomed From The Beginning

Via The Washington Post, a report on the history of the Colorado River Basin system, how it was designed and the impacts of climate change shed light on why it was destined to fail:

For the first time, the U.S. Bureau of Reclamation issued a water shortage for Lake Mead starting in 2022. Located between southern Nevada and northwestern Arizona, Lake Mead provides water and generates electricity for the more than 20 million people in the lower Colorado River Basin.

This shortage isn’t a surprise. Water levels at Lake Mead and Lake Powell to the northeast have already reached historic lows amid the summer drought. By January, the bureau projects water levels at Lake Mead to fall to 1,065.85 feet — nine feet below the first shortage trigger elevation. Levels on Lake Powell, which stores water for the Upper Colorado River Basin, are only marginally better, projected to be just 45 feet above the required elevation to produce hydropower.

The overall situation is not good, but why? This whole reservoir system along the Colorado River Basin was designed to get us through the drought years. Why isn’t it working? A glimpse into the history of the system, how it was designed and the impacts of climate change sheds light on why it was destined to fail — and why it may never recover.

A crash course on the Colorado River Basin

As Americans began moving west, they found that Western rivers behaved very differently from those found in the Midwest and East Coast.

Western rivers were fed by snow from the peaks of the Rocky Mountains. During the winter, river flows would decrease, sometimes even freeze over. As spring and summer arrived, the warmer temperatures melted snowpack that accumulated on the mountains over the winter. Then the melt would run off at exactly the perfect time — the beginning of the growing season. Water would be abundant for farming and other needs during the warm season.

But issues arose with this “perfect” system. People learned less snowfall in one winter would result in less water flowing in the spring and summer. Water might not be as abundant as desired.

Then came an issue of who could use the water. Consider a farmer named Joseph. He and his family would settle on their land and pull from the river during the warm season. It had been a good winter so they expected high river flows that spring. Instead, the flows were really low. Where was his water?

He would go upstream to find that another farmer named William had settled his family there, and he was taking the water. Joseph told William that he couldn’t have the water. But William said it flowed through his land and therefore it was his. Joseph argued that it would actually flow through this land, and he was here first — it was his.

Thus was born the idea of water appropriation, albeit this is an extremely simplified and embellished version of the story.

Later, the Colorado River Compact of 1922 determined the river belonged to all parties where the river and its tributaries flowed. Everyone would share it equitably. This would include the upper basin states (Wyoming, Utah, Colorado and New Mexico) and the lower basin (Arizona, Nevada, and California).

The compact stated the upper basin would share 7.5 million acre-feet per year and the lower basin would also share 7.5 million acre-feet per year. Since the majority of this water originates in the Rocky Mountains of the upper basin states, those states must ensure the consistent delivery of water to the lower basin.

Lake Mead (initially formed by the Hoover Dam in 1935) was designed to hold water for the lower basin states. As an “insurance policy,” the upper basin had Lake Powell, which began filling in 1963. If drought meant the upper basin states couldn’t deliver their promised amount to the lower basin, they could deliver it with water in the savings account of Lake Powell.

While this plan initially seemed to work well, it was doomed from the beginning, for three reasons.

1. The water was already overallocated

How did the compact come up with the number 15 million acre-feet? Well, the number wasn’t just picked out of hat. There was a bit of analyzing of annual precipitation and runoff to come up with the estimate. In the early 1920s, data from the previous 10 to 20 years would be used to calculate the estimate. Unfortunately, the 1910s was a relatively wet decade and skewed the estimates higher than they should have been.

(The Washington Post)

The chart above shows the basin-averaged runoff since 1920, as recorded by the U.S. Geological Survey. There is a lot of year-to-year variability, which is why building reservoirs to store during the wet periods became essential.

The gray line shows what the average runoff was when the compact was written in the early 1920s. Extending the gray line beyond its initiating point, you can see it’s much more common for total annual runoff to come up short. And with each passing year, reaching that gray line becomes even more improbable. The upper basin states consistently owed water to the lower basin that couldn’t realistically and consistently be achieved.

2. Population increases

Today, the Bureau of Reclamation estimates 40 million people rely on water from the Colorado River Basin. When the compact was signed in 1922, the total population of the seven basin states was not even 6 million people.

While the majority of the water from the Colorado River is used for agriculture, the smaller percentage of municipal use can’t be ignored when considering significant population increases. The old rule of thumb is that one acre-foot of water is enough for two households for a year. An increasing number of households throughout the Southwest puts further strain on the already overallocated Colorado River system.

3. Climate change will further reduce water availability in the basin

Temperatures throughout the Colorado River Basin are increasing, with particular “hot spots” in the Rocky Mountains. Scientists are still parsing out precipitation and snowpack trends on the mountains, but higher temperatures alone will reduce the water supply provided by the Colorado River.

For one, an earlier peak snowpack and earlier melt because of a warmer environment reduces runoff efficiency. Higher temperatures allow more water to evaporate into the atmosphere. This increased evaporative demand also means the same level of crop production requires more water.

Climate change is also increasing the frequency and severity of droughts in the Southwest. We’ve seen this quite obviously play out in the 21st century — repeated and prolonged droughts have chipped away at the available water supply while fewer opportunities for recovery have occurred. These trends will continue.

No going back

For many in the upper basin states, the situation became clear after the 2002 drought. The chart below shows how volume has changed in Lake Powell since it was built in the early 1960s. Wetter periods in the 1980s and 1990s helped bring it to “full pool” levels.

(The Washington Post)

The 2002 drought was the most severe drought in the Upper Colorado River Basin in recorded history. To this day, cumulative flows on the Colorado River near the Colorado-Utah state line have not been lower.

While the lower basin states continued a business-as-usual path, it became clear in the upper basin that the system would not quickly recover from this drought. But with each step forward in recovery, another drought would take the system two steps back again.

Upper basin and lower basin states have worked on drought contingency planning, and new adjustments were written after the 2002 drought to prepare for a time when Lake Mead might get too low.

This year, we reached that point. Moving forward, we need to explore other solutions to meet our population and agriculture demands and preserve our forests, rivers and wildlife.

We all must accept that the question is not: “How do we recover Lakes Powell and Mead and get them back to good water levels again?” Instead, we need to ask: “How do we continue to meet the needs of the Southwest without Lakes Powell and Mead?”



This entry was posted on Monday, September 13th, 2021 at 11:26 am and is filed under Colorado River, United States.  You can follow any responses to this entry through the RSS 2.0 feed.  Both comments and pings are currently closed. 

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