Depleted by drought, Lakes Powell, Mead were doomed from start

For the first time, the U.S. Bureau of Reclamation declared a water shortage at 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 — 9 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.

As Americans began moving west, they found Western rivers behaved very differently than 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 on the mountains that accumulated over the winter. Then the melt would runoff 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.

Lake Mead (initially formed by the Hoover Dam built 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? In the early 1920s, annual precipitation and runoff data from the previous 10 to 20 years was used to calculate the estimate. Unfortunately, the 1910s was a relatively wet decade and skewed the estimates higher than they should have been.

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 1 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.

Temperatures throughout the basin are increasing, with particular “hot spots” in the Rocky Mountains. Scientists are still parsing out precipitation and snowpack trends on the mountains, but warmer 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. Warmer 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.

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.