Simulating the effects of weather and climate on large wildfires in France

Abstract

Large wildfires across parts of France can cause devastating damage which puts lives, infrastructure, and the natural ecosystem at risk. In the climate change context, it is essential to better understand how these large wildfires relate to weather and climate and how they might change in a warmer world. Such projections rely on the development of a robust modeling framework linking large wildfires to present-day atmospheric variability. Drawing from a MODIS product and a gridded meteorological dataset, we derived a suite of biophysical and fire danger indices and developed generalized linear models simulating the probability of large wildfires ( > 100 ha) at 8 km spatial and daily temporal resolutions across the entire country over the last two decades. The models were able to reproduce large-wildfire activity across a range of spatial and temporal scales. Different sensitivities to weather and climate were detected across different environmental regions. Long-term drought was found to be a significant predictor of large wildfires in flammabilitylimited systems such as the Alpine and southwestern regions. In the Mediterranean, large wildfires were found to be associated with both short-term fire weather conditions and longerterm soil moisture deficits, collectively facilitating the occurrence of large wildfires. Simulated probabilities on days with large wildfires were on average 2-3 times higher than normal with respect to the mean seasonal cycle, highlighting the key role of atmospheric variability in wildfire spread. The model has wide applications, including improving our understanding of the drivers of large wildfires over the historical period and providing a basis on which to estimate future changes to large wildfires from climate scenarios.

Contrasting large fire activity in the French Mediterranean

“…However, given that SAFRAN is a daily meteorological database, we calculated FWI using maximum temperature and minimum relative humidity as surrogates of noon observations following prior analyses (e.g., Jolly et al, 2015;. Although the FWI was empirically calibrated for estimating whether atmospheric conditions and fuel moisture content are prone to wildfire development in Canada (Van Wagner, 1987), the FWI has already proven useful to track large fires in Mediterranean regions (Dimitrakopoulos et al, 2011) including the French Mediterranean (Barbero et al, 2019). Grid cells of the FWI lying within the study area were first averaged across the June-September season and then averaged across all latitudes spanning the region of interest to form a longitudinal cross section of mean summer FWI conditions.…”

“…It is now unanimously agreed upon that large fires have the most significant socioeconomic and environmental impacts, threatening or damaging infrastructures, ecosystems and even costing human lives, especially in the expanding wildland-urban interfaces (WUIs) (Blanchi et al, 2014;Syphard and Keeley, 2015;Radeloff et al, 2018). However, the definitions of what can be considered a large fire are numerous (Shvidenko and Nilsson, 2000;Stocks et al, 2002;Barbero et al, 2015a;Stavros et al, 2014;Nagy et al, 2018;Tedim et al, 2018), the cutoff being arbitrary or statistically assessed.…”

Current Wildland Fire Patterns and Challenges in Europe: A Synthesis of National Perspectives

“…Over the period 2007-2018, there was an annual average of 4040 fires affecting 11,117 ha of forest in France (BDIF and Prometheus databases). The occurrence of large wildland fires is related to long-term droughts, and in the Mediterranean to the usual summer drought, and specifically the soil moisture deficit (Barbero et al, 2019). This highlights the importance of soil factors in addition to weather conditions for large wildland fire occurrence.…”

“…The majority of large fires occurred in the Mediterranean area (6698 ha, compared to 4419 ha outside this area), and few large wildland fires in the Southern part of France are responsible for the majority of the national total area burned (Barbero et al, 2019). Therefore, some recent investigations were specifically focused on studying the main driving factors and causes of the large fires in this region.…”

Study of atmosphere-wildland fires interactions, using numerical models, in Greece

“…FFWI has been applied to estimate the fire weather severity in the chaparral ecosystems of the Mediterranean-climate southern California during Santa Anna wind events (Moritz et al, 2010;Nauslar et al, 2018). In France, Barbero et al (2019) used the FFWI in a modelling framework for resolving complex relationships linking weather-to-climate variability associated with the occurrence of large wildfires, while Kambezidis and Kalliampakos (2016) introduced a modification of the FFWI that included forest coverage to assess the fire risk in Northern Greece (Central, Eastern Macedonia, Thrace). Goodrick (2002) also modified the FFWI to take into account the impact of precipitation to the index, improving its relationship with the burnt area.…”