Post-wildfire slope stability effects and mitigation: a case study from hilly terrains with unmanaged forest
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Post‑wildfire slope stability effects and mitigation: a case study from hilly terrains with unmanaged forest Luis M. Araújo Santos1,3 · António J. P. M. Correia1 · Paulo A. L. F. Coelho2,3 Received: 29 March 2020 / Accepted: 10 October 2020 © Springer Nature Switzerland AG 2020
Abstract The combined effects of wildfires and storms strongly induce slopes stability phenomena, thus requiring mitigation measures to manage long-lasting wildfire-induced risks. In Portugal, thousands of increasingly destructive wildfires occur during the hottest months. In the last two decades, almost 3,000,000 ha of forest, bush and agricultural land burned in Portugal, 20% of which caused by massive wildfires that occurred in 2017. Portuguese central mountain range was one of the most affected areas, namely the study area of Serra do Açor and Serra da Estrela, where extreme rainfall events in 2018 and 2019 caused extensive slope instability phenomena that created a unique opportunity for assessing long-term field performance of treated and untreated burnt areas. The registered phenomena as well as the treatment solutions applied to mitigate instability effects on slopes were studied in two sites. Over 3 years, several field research trips were carried out to scientifically assess the situation over time. By comparing areas with distinct response to the extreme rainfall events and based on the data collected, namely prior to 2017, it was been possible to link the registered instability events and the October 2017 wildfires and qualitatively evaluate the effectiveness of the adopted mitigation solutions. This study not only confirms that the study area is prone to slope instability wildfire-related phenomena, with a 13-year return period between similar events in the study area, but also validates the use of protective barriers as a mitigation measure, contrary to previous studies carried out in other countries. Keywords Wildfire-related slope instability phenomena · Landslides · Erosion · Slope stabilization · Extreme weather conditions Mathematics Subject Classification 74L10 (Soil and Rock Mechanics)
1 Introduction Each year, Portuguese rural territory is plagued by thousands of wildfires during the hottest months, namely during the so-called Charlie phase, which usually elapses between the first of July and the thirtieth of September [1], 100,000 ha of forests being consumed each year on average [2]. In Portugal, as well in the rest of southern Europe, wildfires are becoming more frequent, not only because
of direct ignition [3], but also because of demographic changes and the increase in flammable biomass [4]. Due to inadequate road network, lack of industry and other socio-economics reasons [5], the population of Portuguese mountain areas has decreased since de second half of the 20th century [4]. In addition to the consequent farmland abandonment, which has favoured horizontal and vertical fuel continuity, the introduction of commercial plantations of fire-prone species, namely maritime pine (Pinus pinaster)
* Luis M. A
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