Wildland fire potential outlooks for Portugal using meteorological indices of fire danger

Abstract

Abstract. Portugal is recurrently affected by large wildfire events that have serious impacts at the socio-economic and environmental levels and dramatic consequences associated with the loss of lives and the destruction of the landscape. Accordingly, seasonal forecasts are required to assist fire managers, thus contributing to alter the historically based purely reactive response. In this context, we present and discuss a statistical model to estimate the probability that the total burned area during summer will exceed a given threshold. The statistical model uses meteorological information that rates the accumulation of thermal and vegetation stress. Outlooks for the 39-year study period (1980–2018) show that, when the statistical model is applied from 26 May to 30 June, out of the six severe years, only one year is not anticipated as potentially severe and, out of the six weak years, only one is not anticipated as potentially weak. The availability of outlooks of wildfire potential with an anticipation of up to 1 month before the starting of the fire season, such as the one proposed here, may serve to provide clear directions for the fire community when planning prevention and combating fire events.

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

“…Yet another approach to wildfire susceptibility is to employ structural variables measured on a seasonal timescale, to predict the severity of wildfires during a later period. These are the cases of Nunes et al (2014Nunes et al ( , 2019 and Pereira et al (2013), who used a cumulative sum of the values of daily severity rating (DSR), obtained through a transformation of the fire weather index (FWI) (Van Wagner 1987). This cumulative index characterizes the moisture state of vegetation during the prefire season (spring to early summer), to predict the severity of wildfires during the ensuing summer period.…”

“…For each of the years between 1995 and 2019, the seasonal severity rating (SSR) was calculated as the cumulative sum of the values of daily severity rating (DSR), from April 1 to June 15. The DSR is obtained through a simple transformation of the fire weather index (FWI) (Van Wagner 1987), and considered more suitable to be cumulated or averaged (Nunes et al 2019). Although the DSR is meant to express the difficulty in controlling wildfire, an elevated cumulative value in the months preceding the summer season indicates the prevalence of relatively high temperatures and low rainfall, which will, in turn, promote water and thermal stress in vegetation in summertime, making it more prone to burning.…”

“…The main advantage of this predictive use of spring/early summer cumulative DSR values is that it allows knowing, ahead of the summer, if the vegetation will be more fire-prone due to the weather effects on water content. This approach has been used by Pereira et al 2013, Nunes et al (2014) and Nunes et al (2019) to anticipate the severity of summer wildfires.…”

“…The importance of weather conditions to fire activity thus justifies their integration as complementary information to structural maps, as we attempt to do in this research. Considering the static nature of the baseline maps we use and the seasonal perspective adopted, a cumulative weather index that represents a seasonal trend was considered more suitable (Nunes et al 2019), thereby requiring a transformation of the daily version obtained from the FWI. What the SSR maps show is the spatial incidence of the deviations in weather parameters, in relation to the average since 1995, disregarding all other factors.…”

Predicting burnt areas during the summer season in Portugal by combining wildfire susceptibility and spring meteorological conditions

“…Nunes et al (2014) to predict the severity of yearly wildfire damage, and more recently by S. A. Nunes et al (2019) to predict the severity of wildfire damage with respect to the summer months of July and August.…”