Research Article: Determining fuel moisture thresholds to assess wildfire hazard: A contribution to an operational early warning system

Date Published: October 4, 2018

Publisher: Public Library of Science

Author(s): Juan P. Argañaraz, Marcos A. Landi, Carlos Marcelo Scavuzzo, Laura M. Bellis, Asim Zia.

http://doi.org/10.1371/journal.pone.0204889

Abstract

Fuel moisture content (FMC) is an important fuel property for assessing wildfire hazard, since it influences fuel flammability and fire behavior. The relationship between FMC and fire activity differs among land covers and seems to be a property of each ecosystem. Our objectives were to analyze pre-fire FMC among different land covers and to propose a wildfire hazard classification for the Sierras Chicas in the Chaco Serrano subregion (Argentina), by analyzing pre-fire FMC distributions observed for grasslands, shrublands and forests and using percentiles to establish thresholds. For this purpose, we used a fire database derived from Landsat imagery (30 m) and derived FMC maps every 8 days from 2002 to 2016 using MODIS reflectance products and empirical equations of FMC. Our results indicated that higher FMC constrains the extent of wildfires, whereas at lower FMC there are other factors affecting their size. Extreme and high fire hazard thresholds for grasslands were established at FMC of 55% and 67% respectively, at 72% and 105% for forests and at 106% and 121% for shrublands. Our FMC thresholds were sensitive to detect extreme fire hazard conditions during years with high fire activity in comparison to average conditions. The differences in the distributions of pre-fire FMC among land covers and between ecosystems highlighted the need to locally determine land cover-specific FMC thresholds to assess wildfire hazard. Our wildfire hazard classification applied to FMC maps in an operational framework will contribute to improving early warning systems in the Sierras Chicas. However, moisture alone is not sufficient to represent true fire hazard in Chaco forests and the combination with other variables would provide better hazard assessments. These operational wildfire hazard maps will help to better allocation of fire protective resources to minimize negative impact on people, property and ecosystems. To the best of our knowledge, this is the first study analyzing pre-fire FMC over several fire seasons in a non-Mediterranean ecosystem, aiming at assessing wildfire hazard.

Partial Text

Wildfires are natural disturbances affecting the composition, structure and processes of landscapes worldwide [1]. However, current fire regimes in many areas are strongly influenced by humans that often increase the number of ignitions and fire frequency. Such departures from natural regimes threaten biodiversity and ecosystem dynamics as well as human life and infrastructure [2–4]. The moisture content of fuels (FMC) is an important fuel property for assessing wildfire hazard, since it influences fuel flammability and fire behavior [5–11]. As FMC increases, the flammability of fuels tends to decrease, because more energy is needed to evaporate water before burning organic tissues. In this context, operational estimations of FMC could be a valuable component of early warning systems [12], helping to minimize the negative effects of wildfires.

Field surveys to collect reference data to derive the land cover map were conducted on public and private lands. F. Barri gave us permission to conduct field surveys on Vaquerías Natural Reserve, which belongs to the National University of Córdoba (Argentina). Field surveys carried out on private lands were conducted with permission of the owners. No permissions were necessary for Province Protected areas because we only visited public lands and we did not collect material. Our field studies did not involved endangered or protected species.

We were able to analyze pre-fire FMC for 11 fire seasons (out of 15). Fire seasons of 2004, 2007 were not included because it was not possible to determine the dates of the fires; however, only five fires larger than 100 ha occurred, accounting for ~ 4,000 ha [36]. In 2015 and 2016, there were no fires larger than 100 ha in the Sierras Chicas. The burned area accounted by fires larger than 100 ha in the 11 fire seasons was 250,052 ha (equivalent to 31% of our study area, and 84% of total burned area between 1999 and 2016).

In this study, we derived fuel moisture maps every 8 days at 500 m spatial resolution for fifteen fire seasons (2002–2016) in the Sierras Chicas in Córdoba (Chaco Serrano subregion of South America) using MODIS reflectance products. Then, we analyzed the relationship between pre-fire fuel moisture content and wildfire size; besides, we analyzed pre-fire FMC for different land covers in order to identify FMC thresholds to assess wildfire hazard. The differences in the pre-fire FMC distributions among land covers highlighted the necessity of determining land cover-specific FMC thresholds to assess wildfire hazard and local thresholds, instead of using those established for other ecoregions. To the best of our knowledge, this is the first study analyzing pre-fire FMC over several fire seasons in a non-Mediterranean ecosystem, aiming at assessing wildfire hazard.

 

Source:

http://doi.org/10.1371/journal.pone.0204889

 

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