Global Warming

Dwindling Colorado River

The Colorado River — which provides water to more than 40 million people from Denver to Los Angeles — has seen its flow dwindle by 20 percent compared to the last century, and scientists have found that climate change is mainly to blame.

The researchers found that more than half of the decline in the river’s flow is connected to increasing temperatures, and as warming continues, they say the risk of “severe water shortages” for the millions that rely on it is expected to grow.

For each 1.8 degrees Fahrenheit of warming averaged across the river’s basin, the study found that its flow has decreased by nearly 10%. Over the course of the 20th and early 21st centuries, the region has already warmed by an average of roughly 1.6 degrees Fahrenheit.

The Colorado River starts high in the Rocky Mountains of Colorado and Wyoming, before snaking its way across the Southwest on its way to the Gulf of California. But by the time it arrives there, its flow is reduced to a trickle, says Brad Udall, a senior climate scientist at Colorado State University who has studied the Colorado River basin for 30 years. En route, water is diverted to supply major cities like Denver, Los Angeles, Las Vegas and San Diego, as well as farms in the US and Mexico that grow the vegetables that feed millions around the world.

Global warming is taking a severe toll on the snowpack that feeds the river, the scientists found. As temperatures increase, snow cover in the region is declining, meaning less energy from the sun is reflected back into space and more warms the ground as heat.

This triggers a vicious cycle that leads to even more evaporation and therefore, less water supply.

The river’s flow has also been diminished by a severe drought that’s spanned much of the last two decades, leaving its two main reservoirs — Lake Powell and Lake Mead — barely half full.

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