These four metrics are used to track drought and paint a grim picture


Drought has tightened its grip on the western United States, as dry conditions enter their second decade and to stretch a river which supplies 40 million people. Experts agree that things are bad and getting worse. But how exactly do you measure a drought and how do you know where it is going?

Brad Udall is an expert on the subject studying water and climate at Colorado Water Center at Colorado State University. Lately his forecast for the basin was not particularly uplifting.

“You can’t watch them without worrying,” Udall said. “Climate models tell us it’s going to get worse. There is every reason to believe it will get worse. It has gotten worse since 2000. What is frightening is that it seems to be getting worse at a faster rate.

He cites four specific measures that scientists use to quantify drought. They are all connected and they all paint a grim picture of what the future may hold.

It all starts with heat

All over the world, temperatures are rising. In the Colorado River Basin, the hottest days are the first domino in a cascade of numbers that tell the story of the drought. In the 21st century, average temperatures in the upper Colorado River basin are 2 degrees Fahrenheit higher than in the previous century.

Climatic conditions in the upper half of the basin are examined under a microscope because this area is where most of the river’s water the water comes from, mostly high elevation snow in Colorado and Wyoming.

Temperatures across the region have been trending steadily upward since the 1980s, and have been particularly high in the very recent past. Between January 2020 and August 2021, the Southwest recorded the third highest daily average temperatures in more than a century.

Alex hager

Heat creates cycles that contribute to drought, drying out the ground and melting snow faster. This leaves less water in the Colorado River, seen here near Page, Arizona.

Udall said the warming is caused by humans releasing greenhouse gases into the atmosphere, which trap and retain heat from the sun.

As every meteorological element undergoes natural ebbs and flows, the heat of the 21st century is extraordinary. Connie Woodhouse is researching the history of climate and water at the University of Arizona. Studies of tree rings, she said, have proven that high temperatures lead to one of the longest droughts in about a millennium.

“It’s different from our long droughts that we have seen in the past,” said Woodhouse. “Even though some of them were during warmer times, they weren’t as hot as the temperatures we see today.

Dry soil prevents water from rivers

You don’t have to be a scientist to notice changes in temperature and precipitation. But another measure that has a disproportionate influence on drought is more difficult to spot without specialized equipment. The quantity of moisture in the soil plays an important role in drought, and high temperatures make conditions drier.

When the rain falls or the snow melts, this water seeps into the earth and flows through the soil to streams and rivers. When the ground is saturated, it can’t absorb much more water – and more of the rain and snow goes to the places where humans divert it and collect it.

But when dry, the soil acts like a sponge, pushing precipitation away from streams and rivers. This sponge effect has been in full effect for the past two years.

02 AH photo of the ground.jpeg

Alex hager

Soil moisture monitoring stations like this one near Glenwood Springs, Colo., Are helping researchers track long-term climate change.

In 2020, the upper basin received 100% of the average snowpack, but because of the dry soil, only 50% of the average runoff. A dry summer after that meant even thirstier soil the following spring. In 2021, the region got 90% of the average snowpack, but only 30% of the average runoff.

This dry soil is also an example of why high temperatures are so important. A warmer atmosphere creates a “feedback loop” with the ground.

“When there is moisture in the soil and the sun beats down on that soil,” Udall said, “this solar energy actually goes into the evaporation of the water, which does not increase the earth temperature. But once the soil moisture is gone, that same solar energy heats the earth’s surface in a really deep way. “

Precipitation is also decreasing

As much as high temperatures and dry soil contribute to drought, so many recent years have also brought bad news for perhaps the most obvious metric: there is less water falling from the sky.

In the southwest, the 20-month period between January 2020 and August 2021 recorded the lowest total precipitation since 1985. A recent report of the National Oceanic and Atmospheric Administration said the numbers appear to be “natural, but unfavorable” – meaning they’re not necessarily due to man-made climate change.

But combined with warm air and dry soil, low total precipitation is an unwelcome contribution to the ongoing drought. When it comes to precipitation, the two decades since 2000 are on par with the worst 21-year period of the 20th century.

Flow rates are low

Across the west, a vast network of streams and streams carry water into the Colorado River. And across the West, they’re all carrying less.

Flow, the last of four measures defining drought, has declined by about 20% over the past century and has declined more rapidly over the past two decades. About a third of the decline is caused by rising temperatures, which can cause evaporation and more spongy soil. The other two thirds are due to the decrease in precipitation.

The warming trend could lead to a further drop in flow rates of 10 to 15% by the middle of this century.

What can be done?

The numbers don’t lie – the conditions are dry and increasingly drier. With tens of millions of people and over a trillion dollars in economic activity relying on the Colorado River carrying enough water for everyone, the stakes are high. So where do we go from here? CSU’s Brad Udall has some good news and some bad news. He thinks it’s in our technological capacity to reverse some of the effects of climate change. But disagreements over Politics and the very facts of climate change stand in the way.

“I fully trust the American people to use our talents, wisdom and compassion for others to help solve this problem,” he said. “But as long as we are divided on this and we do not agree on the causes and the solutions, then it is very difficult to fight this existential threat.”

Brad Udall speaks with reporter Alex Hager about climate change in the Colorado River Basin

Udall is no stranger to the legislative world, coming from one of the most emblematic political families in the West. His father was a congressman from Arizona and his brother was a senator from Colorado.

As the Colorado River Basin embarks on a future of tense negotiations over who can claim its depleted supply, it believes the country will not be able to move away from the worst effects of climate change that are shaping it. .

“If we could be orderly, centered and focused on solving this problem, we could solve it,” Udall said. “What I know. But it’s like trying to fight the Germans in WWII where half the army says ‘oh, these are our friends, these are not our enemies.’ It won’t work with it. a threat of this size.

This story is part of the Continuing Water Coverage in the West, produced by KUNC in Colorado and supported by the Walton Family Foundation. KUNC is solely responsible for its editorial coverage.

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