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Prescribed burns tamp down wildfire threat

Prescribed burns clear out deadwood, forest litter and natural debris that could stoke a wildfire. The fuels could lead to catastrophic event. (Eddie Moore/Albuquerque Journal)

SANTA FE, N.M. — As New Mexico emerges from a winter of sub-par snow, leaving much of the state in extreme drought, the season change seems to naturally steer our attention to the annual threat of wildfires. The National Interagency Fire Center is predicting an above-normal fire risk for the entire state; small blazes have been popping up; and agencies are carrying out prescribed burns. These important, science-based preventive fires are carefully engineered to clear out the deadwood, forest litter, and natural debris that stoke wildfires.

In New Mexico and beyond, climate change is playing a role in the increasing frequency and intensity of wildfires. Hotter days, warmer nights, and less rain trigger a wide range of effects that set up the dry Southwest for bigger, hotter, more socially and economically devastating conflagrations. Fortunately, wildland fire science is delivering tools to help tame fires through decision support for the expanded safe use of prescribed burns and improving knowledge about the feedbacks between natural fires and their environment. The goal is to enable land managers to better anticipate changes in fire behavior and refine practices for keeping blazes from exploding in intensity, scope, and duration.

At Los Alamos National Laboratory, we study climate change and its impact on the environment – both natural and human – because they have a direct impact on the things we care about: national security, economic security, energy security, societal security – in the sense of protecting people from social disruption – and environmental protection, which includes preserving nature and natural resources.

For decades, the Lab has been studying wildfire behavior and its close cousin, prescribed burns. Our work with FIRETEC, a computer modeling tool, springs from related research into the complicated field of fluid dynamics. That branch of science focuses on the motions of gases and liquids, which has applications to our mission of stockpile stewardship science, or assuring the safety, reliability, and effectiveness of the nation’s nuclear weapons. Fluid dynamics apply to lots of other problems, as well – such as wildfire.

FIRETEC lets us take real-world data and plug it into a wildfire simulation on a given landscape. We can drill deeply into how wildfires interact with the atmosphere, terrain, and vegetation, which speed up, slow down, steer, intensify, or calm the fires’ spread. We can explore ranges of conditions such as wind speed and direction, fuel moisture, and so on. Then we can study the sensitivity of the simulated fires to changes in the conditions.

Our research helps the U.S. Forest Service and other agencies understand these complex interactions so they can anticipate the actions of wildfires and plan safe, effective prescribed fires to clear out dangerous fuel like scrub trees, shrubs, grasses, and deadwood without creating a runaway destructive blaze.

In recent research, our team has used FIRETEC and other tools to tease out the influence of subtle factors influencing fire behavior. One project studied an experimental fire at Eglin Air Force Base in Florida under low-intensity fire conditions. We took data from numerous sensors tracking wind speed and direction and then modeled the fire in different ways. We found that small wiggles in the wind sparked big changes in the simulations, revealing how sensitive low-intensity prescribed fire, in particular, is to its environment. This is especially important since prescribed fire managers must anticipate and respond to these kinds of changes.

In other research, we studied how the density and spacing of trees, along with the size and shape of clearings, changes the progression of wildland fires. By modeling the physics of fire-fuel interactions, we found that fires flare up in forests populated by similar-sized trees or checkerboarded by large clearings. Fires slow down where tree size varies. In our modeling, mixing up the sizes and shapes of trees and adding small gaps between trees slowed fires quite a bit, insight that fire managers draw on to create better fire-behavior forecasts.

Fire is a natural part of the environment and brings many benefits to plants and animals. Taking a broader perspective in another project at Eglin Air Force Base, we looked at the healthy role of burns in a changing world where climate-driven disturbances can push an ecosystem past tipping points to become a different ecosystem. In this study, we analyzed how endangered species will respond to altered prescribed-burn timing during the next 80 years of climate change.

We linked prescribed burn scenarios to vegetation models, ran the simulations, and saw which species would survive and grow back, with a focus on endangered species. These findings give land managers information to determine the prescribed-burn frequency that will readjust the vulnerabilities of that altered system to restabilize the ecosystem under its new reality.

On a national scale, we considered how climate change will shift the scheduling of prescribed fires across the United States. First, we looked at the best prescribed-burn conditions – the optimal temperature, humidity, and wind – at seven sites in California, New Mexico, Missouri, Florida and Maine. We then overlaid these conditions onto various climate-model projections through 2099 to see which days, in which seasons, would meet the optimal conditions at each site. Rising temperatures decrease the number of days suitable for safe and efficient prescribed burns in forests and wildlands during the summer. But the upshot is that opportunities for prescribed burning are likely to increase in the spring and fall.

Prescribed fire – intentionally and safely burning a landscape – is a crucial tool for reducing the buildup of hazardous fuels and protecting people, property and forests from the threat of catastrophic wildfire. Prescribed burns also do good work in maintaining fire-dependent ecosystems, improving wildlife habitat, and controlling diseases that can decimate forests. By providing a sharp, clear picture of how fires act on the landscape, wildland fire modeling has become an important tool for planning these controlled burns as well as pinpointing what conditions on the ground can lead to the worst conflagrations so land managers can work to ease those conditions.

Adam Atchley is a hydrologist at Los Alamos National Laboratory, where he studies fire behavior. Alexandra Jonko, also of Los Alamos, is a computational earth scientist studying wildland fire.

 


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