Live Fuel Moisture Content: The ‘Pea Under the Mattress’ of Fire Spread Rate Modeling?

Abstract

Currently, there is a dispute on whether live fuel moisture content (FMC) should be accounted for when predicting a real-world fire-spread rate (RoS). The laboratory and field data results are conflicting: laboratory trials show a significant effect of live FMC on RoS, which has not been convincingly detected in the field. It has been suggested that the lack of influence of live FMC on RoS might arise from differences in the ignition of dead and live fuels: flammability trials using live leaves subjected to high heat fluxes (80–140 kW m−2) show that ignition occurs before all of the moisture is vaporized. We analyze evidence from recent studies, and hypothesize that differences in the ignition mechanisms between dead and live fuels do not preclude the use of overall fine FMC for attaining acceptable RoS predictions. We refer to a simple theory that consists of two connected hypotheses to explain why the effect of live FMC on field fires RoS has remained elusive so far: H1, live tree foliage FMC remains fairly constant over the year; and H2, the seasonal variation of live shrubs’ FMC correlates with the average dead FMC. As a result, the effect of live FMC is not easily detected by statistical analysis.

The Effect of Ecophysiological Traits on Live Fuel Moisture Content

“…Live fuel moisture content (LFMC) is a landscape-level management metric that, along with weather and topography, is incorporated into rate-of-spread models and fire danger ratings [1][2][3][4]. LFMC is expressed as the ratio of water content in fresh plant tissue to the dry weight and represents the amount of moisture that needs to evaporate from a fuel source before ignition can occur.…”

“…For example, wildfire risk increases as LFMC decreases until a critical threshold is reached, and then the fire risk is constant and high [9]. However, recent studies suggest that these breakpoints need to be considered with caution as field-based and laboratory-based studies often show differing results related to the magnitude of the effect of LFMC on fire rate-of-spread [2,4,10]. Hence, further LFMC studies are needed to resolve these issues.…”

A Device for Instantaneously Estimating Duff Moisture Content Is also Effective for Grassland Fuels

“…Live fuel moisture, though, varies more seasonally, depending on the biology of the plant species [12]. While progress has been made in measuring live fuel moisture at broad scales with proxies like soil moisture and via remote sensing [12][13][14][15], obtaining real-time data on live fuel moisture within specific burn units remains a challenge even as wildland fire scientists increasingly recognize the influence of live fuel moisture on fire behavior [16,17].…”

Foliar Moisture Content from the Spectral Signature for Wildfire Risk Assessments in Valparaíso-Chile

“…Furthermore, the wind speed, the fuel moisture content (FMC) and the weight of the fuel bed are some factors on which the wildfire modeling propagation depends [12]. In particular, the fine FMC (live and dead fuels) showed acceptable evidence of producing good results in the modeling of real-world fire-spread rate [13].Fuel Moisture Content, which represents the amount of water contained relative to the amount of vegetation dry mass, can be measured or estimated from field samplings, gravimetric methods, and spectral measurements. The first two methods achieve high accuracy [14], but their results are not extensible at local, regional, and global scales [15]; being the last one the most suitable to larger extension, if the FMC is retrieved from satellite imagery as in [16].…”

“…Furthermore, the wind speed, the fuel moisture content (FMC) and the weight of the fuel bed are some factors on which the wildfire modeling propagation depends [12]. In particular, the fine FMC (live and dead fuels) showed acceptable evidence of producing good results in the modeling of real-world fire-spread rate [13].…”