Experts say last year’s Dragon Bravo Fire had only a limited impact on last month’s deadly flash flood in Grand Canyon National Park.
Following the 145,000-acre blaze, scientists warned the fire could lead to increased runoff and a higher risk of flash flooding throughout the burned area.
That’s not unusual following a wildfire, especially those that are more destructive.
“Fires with moderate to high severity turn the soils more easily erodible. And depending on how long it is after the fire, it takes time for the soils to recover that natural function to resist erosion,” says Abe Springer, a professor of ecohydrogeology at Northern Arizona University.
Springer has studied how water flows on the North Rim.
But he says the canyon country below the rim is also prone to flash flooding.
“This steep topography, rocky, cliff-sided landscape in Grand Canyon naturally always yields more runoff than many other areas,” Springer says. “Other storms and other watersheds have shown that you can get very large floods without burn areas in the park.”
The Bright Angel Canyon was burned less severely than other parts of the Dragon Bravo Fire, Springer adds.
“By far most of the Dragon Bravo fire was in watersheds other than the Bright Angel Creek watershed. And of the Bright Angel Creek watershed, a very small percentage of it was moderate to high severity fire,” he says.
That message has been echoed by meteorologists with the National Weather Service.
“The unburned areas, we think, contributed to the majority of the flooding,” says NWS meteorologist Justin Johndrow. “There was some rain on the burn scar, but it was kind of a small area of the burn scar.”
Storms dumped rain in three waves on Aug. 29, the day of the flooding, and the areas above the canyon on the North Rim were not spared.
According to the National Weather Service, a rain gauge near the park’s developed area recorded more than 2 inches of rain over 24 hours, from 5 p.m. on Aug. 28 to 5 p.m. the following day.
But the inner canyon received the heaviest precipitation — a rain gauge near Phantom Ranch recorded more than an inch in just 30 minutes.
“It was just the intensity of the rain that came through at about 2:30 p.m. [on Aug. 29] was extremely heavy,” says Johndrow. “The ground was already wet. The creeks were already running a little bit, and that half-inch to 1 inch of rain in 30 minutes, mainly over the unburned areas, looks, to us, like what resulted in the flash flooding.”
That sent a mass of water and debris down Bright Angel Creek killing two hikers. Crews continue to search for a third man who is still missing.
The flooding severely damaged miles of the Transcanyon Waterline that supplies the South Rim with drinking water, plunging the park into a water crisis.
Springer says scientists are likely to learn more about the causes of the flooding as data is collected from rain gauges scattered across the North Rim.
But he says the flooding was different from other weather events that the canyon has experienced.
“The unique thing about this flood was it occurred in a place that has a confluence of a high visitor presence in the backcountry and infrastructure that's important to the national park,” he says. “There was real tragedy from this event.”
