A Colorado River Water Primer

Image: Lake Mead is now less than half full (courtesy of Wikipedia Commons)

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A good number of my friends and colleagues have complained that my recent blogs about the Colorado River have been too wonky, too geeky. “They’re boring.” “They’re incomprehensible.”

That has inspired me to break it down. Simplify. Create a primer. Here we go!

This is the Colorado River Basin. It provides water for 40 million people including those living in Los Angeles, Phoenix, Las Vegas, Denver, and others. It irrigates 5.5 million acres of farmland in the US and Mexico.

The basin has historically provided habitat for 33 native fish species including one that has been there since the river began carving the Grand Canyon.

This is how water professionals view the river.

Nearly 100 years ago (in 1922), a group of ‘water buffaloes’ wrote a rulebook (the Colorado River Compact) that allocated the river’s water among seven states. The ‘Upper Basin’ states of Colorado, Utah, New Mexico and Wyoming were given 7.5 million acre feet (MAF) per year. The ‘Lower Basin’ states of California, Arizona and Nevada got the same amount: 7.5 MAF/year. Twenty-two years later, the water buffaloes gave Mexico some water too: 1.5 MAF/year. The fish are still waiting for their water allocation.

Inconveniently, the river doesn’t always produce the 16.5 MAF of water that the water buffaloes gave away in 1922 or 1944. To understand how they made this mistake you’ll need to read this book. Let’s just say: ruh-roh.

That mistake wasn’t such a big deal when there weren’t many people using the river and when the climate was ‘normal.’ But then the desert bloomed with irrigation and the cities swelled and the climate warmed, drying up the river.

More than half of all the water goes to irrigating cattle feed crops. Another one-fourth goes to other crops. Cities and industries take the last quarter. Not a drop flows into the Gulf of California anymore. Twenty-two of the 33 native fish species are now imperiled or extinct.

See that right side of the natural flow graph above? Since 2000, the river’s produced only about 14.5 MAF on average. Some really smart climate scientists say that’s because the climate’s not normal anymore, and the river will be drying more and more each decade. Double ruh-roh.

The people that use water from the Upper Basin figured they were going to be OK for a really long time because they have been consuming only about half of their water allocation each year.

But it turns out that their own water buffaloes didn’t cut such a great deal when the Colorado River Compact was being written. Most scholars (excluding lawyers) assume that the Upper Basin is on the hook to deliver an average of 8.23 MAF/year to the Lower Basin (7.5 MAF for the Lower Basin plus half of Mexico’s share) – no matter how much the upper river is producing. With the river drying up that’s getting harder and harder. Ruh-roh.

Compounding this problem is the fact that the federal managers of the big reservoirs – following their own rules that nobody really seems to understand — have been releasing a lot more than 8.23 MAF/yr from Lake Powell in the Upper Basin, draining the lake in the process. Since 2000, they’ve averaged releases of 8.83 MAF/yr and the lake has lost an average of 0.6 MAF each year. It’s now only half full.

If the lake drops to a critically low level – all it would take is a few years as dry as 2001-2005 — the Upper Basin simply won’t be able to physically release that required 8.23 MAF from Lake Powell. They’ll be in violation of the Compact. Double ruh-roh.

To come into hydrologic balance and remain compliant, the Upper Basin is going to have to negotiate new rules for the federal reservoir managers and keep their current level of use from growing. If only the required 8.23 MAF/yr was being released, Lake Powell would now be full.

Those using water from the Lower Basin have benefitted royally from those higher-than-mandated releases from the Upper Basin. It has enabled them to use a lot more water than they were allocated in 1922. At their peak they were consuming as much as 8.4 MAF, and Lake Mead was evaporating another 0.5 MAF/yr. Ruh-roh.

Since 2000, the Lower Basin has tightened its water belt and averaged 7.5 MAF/yr of consumption – exactly what it was allocated. But with Mead’s evaporation – never accounted for in the Compact allocations – and the requirement to share water with Mexico, the lake has lost nearly 60% of its capacity. Double ruh-roh.

To come into hydrologic balance, the Lower Basin is going to need to reduce its consumption by 18% from its 2000-2018 average. The best way to do this is to pay farmers to grow water.

Class dismissed.