How wildfires beget floods and the delayed danger we ignore at our peril

Last June, two intense and unruly wildfires burned through the Sierra Blanca Mountains around Ruidoso, New Mexico. The South Fork and Salt fires torched 17,066 and 7,688 acres, respectively, leaving a massive “burn scar” above the town, a vacation destination that sits along the appropriately named Rio Ruidoso.

The swath of scorched earth in the mountains is visible from town and will be for years to come. The fires ran along the canopies of the ponderosa pines, spot jumping to create new fires miles away, and were so hot that the ground soil’s composition changed. When wildfires burn at high temperatures like those did, the soil becomes less absorbent and enters into a state called “hydrophobic.”

“You have almost a tin roof or an asphalt effect, where a few inches down below the soil surface, you have what’s called a ‘water repellent layer,’” said Cody Stropki, a wildfire recovery expert and director of resilience at the Phoenix-based SWCA Environmental Consultants.

“That results in water not being able to infiltrate into the soil profile, so it runs off. And right after fire … it’s almost like you’re dumping water onto pavement.”

This changing soil is an increasingly common phenomenon in the West. For years, conditions have been getting hotter and drier with some wildland fire fighters citing noticeably more wind. All of which has led to wildfires — a perfectly healthy part of the West’s ecosystems — that are getting larger and more severe, leaving non-absorbent burn scars behind them.

While the threats imposed from the fires themselves are immediate and obvious, they often overshadow some of the delayed dangers — like hydrophobic soils — that follow.

Many of those dangers are slower moving and passive such as damages to water supplies, vegetation regrowth periods and the countless disrupted hours communities spend recovering and rebuilding. If you’re not living with them, they are easy to overlook.

But some dangers are large enough in proportion that they could even be described as “biblical.” In places with the right degree of pitch, where there is not enough remaining vegetation nor soil able to absorb water, some have the potential to be just as dangerous as wildfires.

Ruidoso Mayor Lynn Crawford said that he was aware of how fires and burn scars beget floods through the town’s prior experience with each, but the South Fork and Salt fires burned across all the watersheds that lead into his town and represented just a different scale of potential.

“When all those watersheds on top of that mountain are burned and you get the slightest amount of rain, it pushes it all downhill,” Crawford said. “And then we’re playing catch, and so it’s ... like a professional baseball pitcher, you know, throwing a ball at a kindergarten catcher.”

He was referring to July 8 when, rather than the “slightest amount” of precipitation hitting Ruidoso’s burn scar, it was a monsoon that dropped 3 inches of rain per hour. The results were broadcast widely.

A shaky cellphone video taken from a porch strung with fairy lights captured a raging torrent of muddy flood water as it flowed through a forest. What was once a creek, had become a 20-foot-deep flash flood roaring its way down the mountain.

Several seconds into the clip, the people recording let out audible gasps. A nearly complete house floats into the frame and floats downstream, one wall dragging in its wake.

“Fifteen minutes before that, you could have jumped across the river ... that home was fine,” Crawford said. “But with the amount of water that came down off that burn scar, it scooped it right up, crashed it into trees and then into our bridge.”

Three people died in those floodwaters, including tragically the two children of a helicopter pilot who was visiting his family from Fort Bliss, Texas. That state experienced a much larger scale of flood related tragedy the same week, with more than 130 people confirmed dead and nearly 100 missing.

Texas’s floods had different implicating factors than those of the communities in the West affected by wildfire, but the scale of all that flood destruction so close together only emphasizes the extreme damage that water can cause.

For the people of Ruidoso, and other mountain communities that exist in sloped areas that intersect with forests — called wildland-urban interfaces or “WUIs” — flooding is not something that might happen. It is something that very much can happen. It might just take more than a year or so to show up.

“If you live in a fire prone area, the threat is real that there could be potential flooding to occur,” Stropki said. “It’s just the reality of living in the mountainous West, where you have steep topography and vegetation that, when you remove it, the water just finds its way downstream.”

How do fires beget floods?

Cody Phelps, the engine boss of the Capitan district of the New Mexico Forestry Division, described the landscape around Ruidoso as one that’s very different from what it used to be 100 years ago. Between the changing weather, humidity dropping, rising temperatures and increased wind, landscapes exist in an environment he likened to a “convection oven.”

Couple that with long periods of governmental policy to suppress wildfires that allowed forests to grow dense with “fuel” — accumulated undergrowth, fallen dead trees and other dried out vegetation — and it is no wonder that fires are burning larger and hotter.

“It is a fire behavior that is not what I would call natural,” Phelps said.

Also referring to the decades of fire suppression, Stropki said, “now we’re at orders of magnitude out of whack in terms of fuel characteristics, trees per acre, tree density. This is on a landscape scale, right? This is millions of acres. This isn’t a small issue.”

And Stropki said those conditions and plethora of fuels are creating fires of a kind that are new to the ancient landscapes of the West, already very familiar with wildfire.

“When you put it in a historical context, a lot of the ecosystems where we’re experiencing this type of damage would never have experienced (fire) behavior like that in the past, just because the (fuel) densities would have never got that extreme,” Stropki said.

Such fires destroy all vegetation and, in the process, turn the ground soil into that “hydrophobic” version of itself. Rain might wash that layer away too, Phelps said, exposing rock that leaves little opportunity for rain to get absorbed into the landscape.

In a normal forest setting, “first the branches intercept some of the impact of the rain. And then it soaks into the duff — the material that’s on the forest floor — and that would help mitigate that pulse of rain," he said. “The whole idea of a forested watershed is it acts like a sponge.”

“Get a glass of water, go to your kitchen table and put a table cloth on it. Pour that water on the table cloth, see what happens,” Crawford said. “Take the table cloth off and take that same glass of water and pour it on that table and then see what happens — and that’s the difference. There’s nothing there to slow it down.”

However, these floods are nefarious in another way. There’s no guarantee that a flood will always follow a wildfire — several significant factors need to align — and it’s a matter of waiting. It may take weeks, months or years for one to show up.

“You need the fire to reach a particular temperature point, literally, to do the damage to the soil that would facilitate faster flows. You need a particular pitch in order for the water to run, and a location for that water to run through,” said Lisa Dale, the director of the climate and society program at Columbia University’s Climate School.

These aren’t ubiquitous circumstances that exist everywhere. But they do exist in much of the intermountain West. Anywhere with steep mountains and intense rains can expect flooding to happen, wrote Charles Shobe, research geomorphologist at the U.S. Forest Service’s Rocky Mountain Research Station, in an emailed response.

Historically, Dale said, the floods mostly affected municipal water supplies, which are often outside the day-to-day imagination of most people. But, she added that, “What we’re seeing now is the scale of these flash floods is becoming their own hazard.”

“Given that the Mountain West and other regions are expected to continue to experience high-severity wildfire,” according to Shobe. “We would expect post-fire flooding to continue to be a significant risk to ecosystems and humans.”

What can be done to mitigate the risks?

One issue is that not all natural disasters are isolated events, but the way that federal relief funding is assessed and distributed is based on each alone. Crawford has to prove to Federal Emergency Management Agency inspectors which damage is from what event in order for money to be released to the town. How can he begin to differentiate between the fires that left the mountains bare and the floods that flowed off of them?

“When we calculate, for example, what a wildfire costs, those calculations are almost always done in the immediate aftermath of the fire. What did it cost to suppress the fire? What did it cost to compensate for insured and uninsured losses?” Dale said.

“But then usually, I don’t know, six months say after the wildfire, those calculations end. And yet, many of the most expensive and long-term costs are just beginning and flooding is one of them.”

When the costs to address the damage and put in preventative measures can cost towns billions, according to Crawford, it’s a large, arduous bureaucratic hassle to get just a few million.

Ruidoso is now in a cycle where the floods will likely continue for years to come. There was more rain on the horizon after the floods, and this week there is rain on the forecast nearly every day. The community is actively working with FEMA to receive whatever funding is available in order to address the burn scar.

Outside of the damage to homes and businesses (300 homes were affected, and nearly 200 were totaled, the mayor said), the town also needs to address the scar and runoff leading to the town.

“Time is the healer, but we have got to do things to help ourselves, which is manage the forest, have selective thinning, get rid of invasive species,” Crawford said. “Then start terracing ... so, it creates a little berm and then a little silt is left and dirt and then seeding takes hold. And we make it where this water is diverted over this way, over that way, down and around to take that speed out of it.”

But to really get ahead of the fire and flood cycle, there are things that individuals and communities can prioritize.

For individuals, Wildfire Risk to Communities, a website managed by the U.S. Forest Service, is a great place to begin. It has detailed advice on everything from building materials through creating a defensible space around properties. It also has suggestions for elected officials.

Like Crawford mentioned, Phelps and Stropki emphasized thinning forests on federal land. Less fuel would help mitigate the temperature and scale of future wildfires. Several studies have shown that to be an effective way to limit wildfire’s severity.

“In the absence of doing those things, we’re definitely gonna have more flash floods following wildfires,” Dale said.

Just like the town of Ruidoso. But Crawford remains hopeful. He pointed out that local archaeologists found evidence of human habitation in the area that’s 6,000 years old. He’s going to keep working to try and keep folks safe in the valley, living alongside those threats.

“What we’re learning is, it’s a part of life these days,” Crawford said. “We experienced the fire a year ago in June, and that is where all this started. This is going to be the new normal for the next three to five — or maybe longer — years.”

“It’s a whole diversity of stuff that will cause you anxiety,” he added. “And that’s where we’re at. But then, every night we go to bed, I have this imaginary picture of the mountain with the burn scars on them.”