Understanding Wildland Fire Modeling Leads to Better Predictions

Learning how wildland fires behave scientifically provides a better chance at accurately predicting the spatial and temporal evolution of high intensity wildfires, said Dr. Shankar Mahalingam, dean of the UAH College of Engineering, and professor of Mechanical and Aerospace Engineering.

Dr. Mahalingam is studying how wildland fire propagates in an effort to be able to more accurately model such fires via physically based computational models. He said he’s confident that the day will come when wildland fires will be forecast using computer models just as accurately as the next day’s weather forecast.

When wildland fuel distribution and ignition potential can be very closely assessed, and the regions within a fire where intense energy in the form of heat is released can be accurately determined, the rate and area of a fire’s spread can be predicted days in advance. That will open doors to scientific advances in everything from firefighting technologies to firefighting resource logistics and can even influence the design of subdivisions, developments and homes, says the UAH researcher.

High confidence in the reliability of fire prediction is lacking today, even as Western drought and the effects of climate change drive up the total acres burned nationwide and also the average size of each fire, ballooning the number of on-call U.S. Forest Service firefighters and the total costs to battle the flames.

A single battle with a large wildfire can incinerate $1 million a day in firefighting costs, a total that has exploded annual national costs to nearly $2 billion recently, even as states ante up an additional $1.5 billion.

Even though U.S. wildfires are seen largely as a Western problem, in 2013 Alabama’s 1,284 wildfires – including some large springtime blazes – burned 25,623 acres in the state. That’s slightly over 40 square miles of land.

According to Dr. Mahalingam, current fire behavior models can only predict low intensity fires.

Today, most fire behavior predictions rely largely on the “pure experience” gained by firefighters and managers who have fought blazes for years, he said.

Wildland fires involve complex interactions that include fuel distribution, terrain topography, chemical reactions, energy transfer and the associated fluid dynamics that transport moisture, gas-phase hydrocarbons, air and products of combustion.

“Where the energy is released is what is going to dictate the fluid dynamics in the vicinity,” he said.

In turn, the fluid dynamics of the air and combustible hydrocarbons as fire progresses could point the way to where the fire will spread.

The process begins with pyrolysis, the thermochemical decomposition of organic material at elevated temperature. Energy released by fire heats and converts heavy hydrocarbons in the materials burning into light gaseous hydrocarbons that are more readily burned.

“Fire is a process in which the energy release will drive the airflow around it and the resulting fluid dynamics will in turn drive the fire,” he said.

Continual warming of the leading edge of the fire is a necessary precondition to releasing the chemicals in the fuels that are needed to sustain it.

During his research, he found that wind and moisture are factors that affect fire spread.

“I was studying marginal burning behavior, which I call a fire transition phenomena,” Dr. Mahalingam said. “Fire is losing heat through radiative and convective heat transfer and it is gaining heat as energy is produced as a result of combustion, so it is an energy balance problem.”

UAH scientists are looking at how the interaction of fires in shrubs near each other can create energy hot spots in a conflagration. Shrubs burned in controlled settings are being compared to computer modeled shrub fires to assess predictive qualities.

“As you bring the shrubs closer together, is the fuel being consumed faster and the energy created faster as a result? We are interested in how the fire spreads from shrub to shrub, what the interaction is, and at what spacing and what the wind’s effects are. It turns out that for cases with no wind, you really have to get the shrubs close together for one to affect the other,” the researcher said.

“My hope is that the time period of fire prediction can be extended to several day and nighttime cycles ahead,” he said. “You have to include the nighttime cycles separately because they present a very different set of atmospheric circumstances for the fire.”

Source: University of Alabama Huntsville