A combined structural and seasonal approach to assess wildfire susceptibility and hazard in summertime

Abstract

Wildfire susceptibility and hazard models based on drivers that change only on a multiyear timescale are considered of a structural nature. They ignore specific short-term conditions in any year and period within the year, especially summer, when most wildfire damage occurs in southern Europe. We investigate whether the predictive capacity of structural wildfire susceptibility and hazard models can be improved by integrating a seasonal dimension, expressed by three variables with yearly to seasonal timescales: (1) a meteorological index rating fuel flammability at the onset of summer; (2) the scarcity of fuel associated with the burned areas of the previous year, and (3) the excessive abundance of fuel in especially fire-prone areas that have not been burned in the previous ten years. We describe a new methodology for combining the structural maps with the seasonal variables, producing year-specific seasonal susceptibility and hazard maps. We then compare the structural and seasonal maps as to their capacity to predict burnt areas during the summer period in a set of eight independent years. The seasonal maps revealed a higher predictive capacity in 75% of the validation period, both for susceptibility and hazard, when only the highest class was considered. This percentage was reduced to 50% when the two highest classes were considered together. In some years, structural factors and other unconsidered variables probably exert a strong influence over the spatial pattern of wildfire incidence. These findings can complement existing structural data and improve the mapping tools used to define wildfire prevention and mitigation actions.

Assessing Wildfire Exposure to Communities and Protected Areas in Portugal

“…On average, some 18,345 fires in Portugal annually burned about 138,841 ha during 2009 to 2018 years [37], 0.2-6% of the area per year. Still, the bulk of the fire is concentrated in a relatively small portion (~10%) located in the central and northern regions, where 905,932 ha have been burned at least twice in the last 30 years (i.e., average fire recurrence interval < 15 years) [28,38].…”

Wildfire Risk Levels at the Local Scale: Assessing the Relative Influence of Hazard, Exposure, and Social Vulnerability

“…Wildfires are becoming more harmful, with recent events occurred in Southern Europe, South America, USA and Australia showing their potential destructive power [1][2][3]. In Portugal, wildfire is one of the most impactful hazards, with the extreme events occurred in 2017 causing the most devastating consequences ever recorded, including the loss of over 100 human lives [4,5]. Especially in the inner part of the territory, the combination between the abundance of flammable forest and shrubdominated land cover, the warm and dry summers typical of Mediterranean-type climates, and the irregular topography, creates a particularly challenging fire-prone landscape [6][7][8][9].…”

“…Especially in the inner part of the territory, the combination between the abundance of flammable forest and shrubdominated land cover, the warm and dry summers typical of Mediterranean-type climates, and the irregular topography, creates a particularly challenging fire-prone landscape [6][7][8][9]. Historical data also shows that, between 1980 and 2018, Portugal had the highest average number of annual wildfires and the second largest annual burnt area among the top affected countries of southern Europe (Portugal, Spain, France, Italy and Greece) despite having the smallest territory [5]. Most of the damage occurs in the summer months as the consequence of a relatively small number of large fires [9][10][11][12].…”

Uncovering Vegetation Changes in the Urban–Rural Interface through Semi-Automatic Methods

“…Forest fires are related to the spread of fire in forest areas and savannahs, and usually occur in periods of drought where there is less moisture available [1]. Portugal, despite having the smallest territory of the southern European countries (i.e., Portugal, Spain, France, Italy, and Greece) is one of the most affected [2]. To Portuguese civil protection [3], forest fires are considered as one of the most serious natural disasters due to their high frequency and extent that they may cover.…”