Photograph by Rick Wilking, Reuters

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A home and car are stranded after a flash flood in Coal Creek destroyed the bridge near Golden, Colorado, September 12, 2013. Scientists say drought, fires, and global warming may have helped spur the flood.

Photograph by Rick Wilking, Reuters

Amid Drought, Explaining Colorado’s Extreme Floods

Flash floods in Boulder area may also have ties to fires and climate change.

This story is part of a special National Geographic News series on global water issues.

University of Colorado, Boulder law school professor Brad Udall has long written and lectured about water issues in the American West, but this week’s Colorado floods have brought the subject to his doorstep.

Four people have lost their lives in flooding this week that has engulfed swaths of Colorado and that has forced thousands to evacuate their homes.

Udall, director of the University of Colorado, Boulder’s Getches-Wilkinson Center for Natural Resources, Energy and the Environment says that the Boulder area (see map) has received more rain in the past three days (up to 15 inches, or 38 centimeters) than the previous precipitation record for a whole month.

Udall’s house sits about 30 feet (9 meters) from a creek that is normally dry this time of year. In the past two days, he said the creek rose more than five feet (1.5 meters), and has become a raging stream that’s 20 feet (6 meters) wide.

“[Thursday] night I had a hard time going to sleep because of the ominous rumblings of large boulders tumbling down the creek bed,” Udall said. His house narrowly escaped major damage, but many neighbors weren’t so lucky.

U.S. President Barack Obama declared an emergency for Boulder, Larimer, and El Paso Counties on Friday and the Federal Emergency Management Agency (FEMA) has deployed four rescue teams to the area, the most ever in the state.

Just as troubling as all the damage, Udall says, is that this week’s floods do not fit into the usual pattern of high water in the West.

The floods were not the result of springtime rains or intense summer thunderstorms that quickly dump large amounts of rain in concentrated areas, such as the 1976 Big Thompson or 1997 Fort Collins floods.

“This was a totally new type of event: an early fall widespread event during one of the driest months of the year,” Udall said.

So what explains the anomaly?

Sandra Postel, National Geographic’s Freshwater Fellow, said that the long-term drought that has parched the area and gripped much of the Colorado River Basin over the past 14 years may be partly to blame for the severity of the floods.

Drought tends to harden the soil, she said. When rains do come, less of the water can absorb into the ground, so it quickly runs off the land.

Similarly, fires can lead to worse flooding, because they remove vegetation that can slow down and trap rainfall, Postel said. (See “Fire and Rain: The One-Two Punch of Flooding After Blazes.”) In 2012, the Boulder area was afflicted by the Flagstaff Fire. In 2010, the Fourmile Canyon fire caused damage to Boulder County worth $217 million.

Scientists have warned that increasing frequency and severity of wildfires and droughts may be symptoms of climate change, as much of the planet warms. That, in turn, can lead to more floods.

In June, President Obama told an audience at Georgetown University, “Droughts and fires and floods, they go back to ancient times. But we also know that in a world that’s warmer than it used to be, all weather events are affected by a warming planet.”

Udall said that while current science can’t pin any particular extreme weather event to climate change, this week’s flooding is likely a reflection of global warming, at least in part.

The connection, he said, “might be 10 percent or it might be 90 percent, but it isn't zero percent and it isn’t 100 percent.”

Udall added that warmer air means more moisture can be held by clouds, which can lead to more rain:“As the climate warms further, the hydrologic cycle is going to get more intense.”

“Between the fires last year and this year, the unprecedented and continuing drought in the Colorado River, and now this shocking event,” he continued, “climate change feels very real to me.”

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