A Statistical Analysis of Energy Release Component for Large Wildland Fires on the Southern Great Plains

Although weather has long been recognized as the most dynamic variable to influence wildland fire behavior, the wildland fire environment is actually a complex system where weather and ambient vegetative fuels combine to parameterize potential fire intensity and spread. This is particularly true in the grass-dominated fuelscape of the southern Great Plains, where dramatic biophysical responses of herbaceous-type vegetation to both short-term meteorological and seasonal climatic variation is a critical influence on significant fire potential. Within the southern Great Plains ecosystem, fine short- and mixed-grass prairies are the primary catalyst for extreme rates of fire spread, while the presence of intermixed shrub influences fire intensity and resistance to control. This study provides a statistical analysis of Energy Release Component (ERC, fuel model G) associated with 201 large wildfires (≥121 ha) that occurred on the southern Great Plains of New Mexico and Texas between 2006 and 2011. ERC, a quantity directly related to the total energy per unit area of vegetation, cumulatively applies effects of day-to-day weather on curing and drying of available fuel loads over time. A vast majority (84%) of large fires occurred when ERCs were in excess of local 75th percentile values of 56 and 43% exceeded 90th percentile values of 67. Median and mean ERCs associated with large wildfires on the southern Great Plains were 64 and 65 respectively. The data suggest that operational thresholds of ERC based upon local critical percentile values have utility in improving Red Flag Warning services. As such, a matrix for combining weather and fuels via Red Flag Threat Index and ERC is shown to provide context for defining significant fire potential levels relative to historic fire occurrence.