Fire from the Sky in the Anthropocene

Abstract

[EN] Lightning is the prevailing ignition source in many remote or scarcely populated parts of the world, and those fires tend to be larger and more intense than human-caused fires [1]. “Dry” lightning storms can ignite many fires over short periods of time and relatively vast areas and in locations less predictable and accessible than those of human-caused fires. Additionally, and regardless of the ignition cause, thunderstorm wind flows can drastically change the behaviour of on-going fires, amplifying fire–atmosphere interactions and leading to erratic and destructive firestorms. Such was the case of the Pedrogão Grande wildfire in Portugal, where 66 people died on 17 June 2017 [2]. Fires themselves can generate lightning when pyrocumulonimbus form, as in the Black Saturday fires of February 2009 in Australia, where 173 people perished [3]. In 2019–2020, the unprecedented Black Summer mega-fires were mostly lightning-caused fires (LCFs) and burned one-fifth of the Australian temperate broadleaf forest and caused huge social disruption [4]; lightning started most fires in a region where “dry” thunderstorms are now more frequent than in the recent past [5]. Once rare in Tasmania, LCFs are now threatening World Heritage forests non-adapted to fire [6]. In California, the unusual 2020 lightning siege has burned ca. 1 million hectares, destroying at least 4390 structures and killing 22 people after 14,000 lightning strikes [7]. In human-dominated landscapes, such as in southern Europe, LCFs comprise a small fraction of the total number of fires, and so are commonly perceived as irrelevant. Such neglect and focus on human agency can happen even when fire statistics indicate a significant role of LCFs in the fire regime, e.g., in temperate Australia [8]. Consequently, by downplaying or ignoring LCFs, fire management planning will hardly be prepared to handle the particular difficulties posed by an LCF crisis. Here, we characterize the relevance of LCFs in a generically low LCF region, the Iberian Peninsula, and will then address current and future challenges posed by LCFs in relation to climate change