What Drives Periods of Rapid Fire Spread?

Tempest McCabe,  NASA GSFC / UMD,  tempest.mccabe@nasa.gov (Presenter)
Eli Orland,  NASA GSFC / UMB,  elijah.orland@nasa.gov
Robert Field,  Columbia University,  robert.field@columbia.edu
Shane Coffield,  NASA GSFC / UMD,  shane.coffield@nasa.gov
Alexey Shiklomanov,  NASA GSFC,  alexey.shiklomanov@nasa.gov
Melanie  Cook,  NASA GSFC,  melanie.cook@nasa.gov
Douglas Morton,  NASA GSFC,  douglas.morton@nasa.gov

Extreme wildfires threaten lives, property, and ecosystems. Is extreme fire behavior driven by weather, or by fuels? Large fires can experience “runs” or “spread-days” where fire perimeters expand quickly, and “stay-days” where fires continue to burn but the perimeter expansion is slow. How significant spread-days are to a region’s fire regime and the conditions that drive shifting between stay-days and spread-days are not well understood.
We investigated spread-days in the Western United States 2020 fire season (May-October) using sub-daily information on fire area measured by the VIIRS sensors on the Suomi-NPP and NOAA-20 satellites. We compared days of high-spread, “spread days” to days of low spread, “stay days”. We classified spread-days within the multi-day time series of fire expansion for each fire event, and then compared our fire-spread time series to a gridded Fire Weather Index (FWI) product based on satellite precipitation data (IMERG). Finally, we looked at the relationship between fire radiative power, spread, and post-fire classification of severity by the MTBS program for 2021 Caldor fire.
We found that on average 60% of a fire’s final area accumulates during spread-days, and that the fraction increases with larger fires. Across all fires larger than 5 km^2 (n = 405), 85% of the total fire area came from a spread-day. Ignitions (new fire starts) were associated with the highest 48-hour-lagged FWI values, and spread-days were associated with higher 48-hour-lagged FWI values than stay-days. Ignitions and spread-days for ongoing fire events were synchronized across the western US during the 2020 fire season. In the Caldor fire, we found that periods of rapid fire spread were also more intense, leading to higher soil burn severity.
These findings suggest that most of the total burned area for a given fire event occurs during days when a fire is spreading quickly, and that fires are more likely to spread under the dry, hot, and windy conditions. The clustering of spread-days across the Western US suggests that FWI may explain aspects of fire-behavior better than local conditions like fuel and topography. Spread-days may also explain differences in fire-severity within the footprint of a single fire, providing important context for assessments of post-fire impacts.

Poster: Poster_McCabe_3-16_146_35.pdf 

Poster Location ID: 3-16

Presentation Type: Poster

Session: Poster Session 3

Session Date: Thu (May 11) 3:00-5:00 PM

CCE Program: Other