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In roughly 50 percent of New Mexico, Arizona, and west Texas, wildfires that burn across hard-baked desert landscapes need annual/invasive herbaceous and other fine fuels to drive them.

Mod-FIS map of in-season annual grass conditions for SW United States and Great Basin
This graphic of the in-season condition of annual grasses in the U.S. Southwest and Great Basin was created with LANDFIRE’s Modeling Dynamic Fuels with an Index System, or MoD-FIS. The summer of 2020 fuel vegetation cover was updated using Landsat Normalized Different Vegetation Index imagery from Feb. 1 to September of 2020, and is useful in informing wildland fire conditions.

For fire managers and those who do modeling, understanding when and where those fuels are present, how abundant they are, even how tall they are, is all vital to preparing for a fire season and addressing wildfires as they’re happening. Those people need to know how seasonal variation changes over time and thus affects fire behavior.

The Landscape Fire and Resource Management Tools Program (LANDFIRE) has developed a product to aid with that understanding. It’s called Modeling Dynamic Fuels with an Index System, or MoD-FIS. What it does is capture the seasonal variations in the production of herbaceous cover such as Buffelgrass and other annual/invasive herbaceous grasses.

Fire modelers have long relied on fuel layers produced by LANDFIRE for information representing average conditions and updates for disturbance on the landscape. While incredibly useful, Landsat data used in producing those fuel layers have been only updated every two years, meaning modelers don’t have the information they need to identify extreme drought or precipitation events in between those updates. Several years ago, modelers participating in post-fire season conversations began to make the case for more timely data in the Southwest and Great Basin, said Charley Martin, a fuel specialist with KBR and a contractor to the USGS.

Assessing Current Abundance of Fine Fuels

LANDFIRE staff responded by taking 10 years of Normalized Difference Vegetation Index (NDVI) information from Web-enabled Landsat Data (WELD) and analyzed it to determine the historical average and range of vegetation greenness values for each pixel across a region. These values were correlated with current Landsat imagery to measure LANDFIRE herbaceous cover to determine the current abundance of fine fuels. Using current year herbaceous cover, the LANDFIRE Total Fuel Change Tool can make the fire behavior fuel model changes that reflect the current fire season herbaceous cover and resultant fuel availability.

As a result, fire managers and modelers are now getting updated Existing Vegetation Cover, Existing Vegetation Height, and Fire Behavior Fuel Model layers.

Today, LANDFIRE is providing three updates per fire season on the annual/invasive herbaceous grass situation in the Southwest and Great Basin—by June 1 for the Southwest, by July for areas further north in the Great Basin, and by October 1 again down in the Southwest as monsoons come up from the southern latitudes and lead to invasive grass growth.

Those updates are particularly helpful in informing a strategy on how to deal with fire incidents, said Chuck Maxwell, a fire meteorologist with the U.S. Fish and Wildlife Service. Fire modeling that is informed by MoD-FIS helps managers determine where a fire is likely to go, he said. It can help identify how hot it’s going to be, how fast it’s going to move, and where the firefighters should go, as well as the number of firefighters and resources needed.

 “Everything is based on that base intelligence,” Maxwell said. “Fire behavior drives the bus, and if you don’t have the right fuel model in there, you aren’t getting the right fire behavior.”

Wildland Fire Managers, Analysts Using MoD-FIS

Mod-FIS map of in-season annual grass conditions for SW United States
In-season condition of annual grasses in the U.S. Southwest for Fall 2020, created with LANDFIRE’s Modeling Dynamic Fuels with an Index System, or MoD-FIS. 

In the Great Basin/Southwest, fire modelers traditionally access LANDFIRE base fuel layer data from a system called the Wildland Fire Decision Support System, or WFDSS, when they’re dealing with current fires. The WFDSS system feeds LANDFIRE base data into models (Basic/Nearterm – Farsite/FSPro) that provide information such as hourly projections of where fire will go, what the fire behavior is capable of in certain areas, and what a fire may look like over the next 14 days based on weather and other inputs.

Martin sees more wildland fire mangers and fire behavior analysts grabbing the MoD-FIS data, “and that’s what they’ll use to get a projection on current ongoing fires,” he said.

In the southeastern U.S., the issue is less about annual/invasive herbaceous grasses and more about drought.

“When plant life submerged beneath water is exposed as that water recedes because of drought, it becomes fuel for fires,” Martin said.

As that happens, the provisional MoD-FIS product is applied to the Keetch-Byram Drought Index (KBDI) to help account for the seasonal drought condition.

“As the soil moisture is depleted, we have break points for the KBDI index,” Martin said. “When it hits these break points ... if the current fuel model isn’t going to project fires for that kind of a drought situation, we alter the fuel model to something that will project fires for that situation.”

The bottom line is, MoD-FIS is a product that’s being used successfully across wide segments of the United States. Fire managers and modelers are using it in the desert Southwest, in California, New Mexico, Arizona, and west Texas, where the emergence of fine annual/invasive herbaceous fuels on hard-baked landscapes can feed wildfires. MoD-FIS is proving valuable throughout the Great Basin, from central Texas through central Colorado, into a small portion of Wyoming and then into parts of Montana, most of eastern Oregon, southern Idaho, and over to the West Coast.

Again, it’s also being used heavily in the Southeast, from east Texas up through eastern Oklahoma, into Missouri, and everywhere east of there to the Atlantic Ocean.

In all those places, fire managers and modelers studying LANDFIRE fuel layers and trying to assess the potential fuel loads for existing or future fires now have another important fire modeling and management tool. They have MoD-FIS.

“When they run their models with the updated information from MoD-FIS, you see what is actually happening,” Maxwell said. “So yeah, this product, it’s a huge deal.”

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