Interactions between hot and dry fuel conditions and vegetation dynamics in the 2017 fire season in Portugal

Abstract

Wildfires are a serious threat to ecosystems and human. In Portugal, during 2017, a catastrophic fire season burned more than 500 000 hectares and caused the death of more than 100 people. Previous studies have shown that hot and dry fuel conditions promoted widespread propagation of wildfires. However, burned area (BA) and mega-fires, such as the 2017 ones, depend not just on favourable meteorological conditions, but also on fuel accumulation and dryness. In this study, we will assess the influence of spring meteorological conditions on fire season BA, through their effects on fuel accumulation and dryness. Using satellite-based data, we show that the association of higher temperatures and water availability in spring can increase the risk of summer wildfires propagation, flammability and intensity through their influence on vegetation gross productivity. This study highlights the important role of fuel accumulation during the growing season in fire-prone regions like Portugal. Our results imply that fuel management may be an effective way to mitigate extreme fire seasons associated with warmer and drier conditions in the future.

Mapping the Most Susceptible Regions to Fire in Portugal

“…Moreover, the results also agree with Mateus and Fernandes' [63] observations, in the way that the extreme fire seasons in Portugal are strongly linked to the association of fuel accumulation availability with hot and dry conditions, which was also pinpointed by Gouveia et al [18] and Ermitão et al [19]. Some of the most susceptible areas to fire have burned in the last years, especially in 2017, when wildfires devastated the central part of the country [10,19,20]. Our analysis relied on a dataset of around 20 years (depending on the variable) and indicated that, despite the recent occurrence of fire events, those areas constitute a hotspot and have a great potential to burn in the near future.…”

“…Therefore, although we do not directly address an analysis for hot and dry conditions in ecosystems, our results of fire weather conditions are in line with Pausas and Fernández-Muñoz's [62] insights. Moreover, the results also agree with Mateus and Fernandes' [63] observations, in the way that the extreme fire seasons in Portugal are strongly linked to the association of fuel accumulation availability with hot and dry conditions, which was also pinpointed by Gouveia et al [18] and Ermitão et al [19]. Some of the most susceptible areas to fire have burned in the last years, especially in 2017, when wildfires devastated the central part of the country [10,19,20].…”

“…Studies related to the identification of areas with wildfire susceptibility in Portugal have been performed during the last years, mainly since the harsh fire season of 2017. The centre of the country was strongly disturbed by the wildfires of this year [10,19] and these events left deep scars in vegetation, which remained for a long period. Relying on variables related to elevation and slope angle, which have a strong influence on vegetation distribution, flammability and local climate [64], and land cover and fire weather indices, these studies mapped the areas with high exposure and vulnerability to fire in the country [23,29,31].…”

“…Among the Mediterranean countries, Portugal has been recording a high extent of burned areas during the last decades [10]. Hundreds of thousands of hectares have burned, and a wide range of studies have shown that the recent occurrences of extreme fire seasons, such as in 2003, 2005, and 2017, were closely linked to anomalous hot and dry summers, and also to high fuel availability, promoted by favourable conditions in the pre-fire season [10,[18][19][20].…”

The severity of dry and hot climate extremes and their related impacts on vegetation in Madagascar

“…Apart from the documented association between droughts and heat extreme events in certain parts of the world, their influence on vegetation activity has been also analyzed during the last years. 5 , 24 , 25 , 26 , 27 , 28 Previous studies pointed out that the depletion of soil water content amplifies high temperatures due to the increase of sensible heat fluxes, 29 leading to a consequent reduction in the transpiration and photosynthetic activity of vegetation, 30 which on the other hand can lead to severe wildfires and consequently to considerable economic, social, and environmental damages. 31 Moreover, the land-atmosphere-vegetation interplay can occur with different levels of damage, even for low-intensity extremes, 32 and its highly dependent on the land cover.…”