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Communication Dans Un Congrès Année : 2019

Does large fire activity vary within the French Mediterranean area?

L'activité des grands feux varie-t-elle en région méditerranéenne française?

Résumé

In the French Mediterranean, large fires have significant socio-economic and environmental impacts. The previous works dealing with fires in the French Mediterranean were based on gridded fire data commencing from the mid-1970s (e.g., Ruffault et al., 2016; Fréjaville and Curt, 2017; Ganteaume and Guerra, 2018; Lahaye et al., 2018). Working with longer time-series of georeferenced fires (extending back to 1958) would allow examining both spatial and temporal distributions of large fires (>100 ha) across the French Mediterranean. The objectives of this work were (i) to identify the locations associated with large fire recurrence and to quantify the spatial extent of the region with reburns, (ii) to establish the mean fire extent and the fire return level as well as the LF causes along a longitudinal transect spanning the study area (identifying possible roles of climate conditions and fuel continuity in shaping this longitudinal gradient), and (iii), building on previous research, to re-estimate trends in large fires across the region taking advantage of a fire record spanning almost six decades. A long-term geo-referenced fire time series (1958-2017) was used to analyse both spatial and temporal distributions of large fires (LF; ≥100 ha). Large fire causes were analysed according to the regional fire database Promethée that has recorded fires since 1973. The region was impacted in some locations up to 6 times by recurrent LF (Fig. 1) and 21% of the total area burned by LF occurred on a surface that previously burned in the past, with potential impact on forest resilience. We found contrasting patterns between the East and the West of the study area, the former experiencing fewer LF but of a larger extent compared to the latter, with an average time of occurrence between LF exceeding 4,000 ha 50 years in the West. This longitudinal gradient in LF return level contrasts with what we would expect from mean fire weather conditions strongly decreasing eastwards during the fire season but is consistent with larger fuel cover in the East, highlighting the strong role of fuel continuity in fire spread (Fig. 2). Figure 1: Fire recurrence on the 1961-2017 and 1958-2016 period in the western and eastern areas, respectively. Figure 2: Top) Longitudinal cross-section of mean LF extent computed over 30-km sliding windows. The 95% confidence intervals were estimated using a bootstrapping approach. Bottom) Same as top panel but for mean June-September FWI (in red) and the percent of biomass (in green). Additionally, our analysis confirms the sharp decrease in both LF frequency and burned area in the early 1990s, due to the efficiency of fire suppression and prevention reinforced at that time, thereby weakening the functional climate-fire relationship across the region. Regarding the causes of LF, the proportion of unknown cause was high throughout the region, varying from 74% to 77% from the West to the East. It is worth noting that the knowledge of smaller fires
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Dates et versions

hal-02609866 , version 1 (16-05-2020)

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Anne Ganteaume, R. Barbero. Does large fire activity vary within the French Mediterranean area?. 6th International Conference on Fire Behavior and Fuels, Apr 2019, Marseille, France. pp.16. ⟨hal-02609866⟩
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