• Energy Research

Fire's growing impacts on ecosystems Fire has played a prominent role in the evolution of biodiversity and is a natural factor shaping many ecological communities. However, the incidence of fire has been exacerbated by human activity, and this is now affecting ecosystems and habitats that have never been fire prone or fire adapted. Kelly et al. review how such changes are already threatening species with extinction and transforming terrestrial ecosystems and discuss the trends causing changes in fire regimes. They also consider actions that could be taken by conservationists and policy-makers to help sustain biodiversity in a time of changing fire activity. Science , this issue p. eabb0355

AbstractBackground‘Megafire’ is an emerging concept commonly used to describe fires that are extreme in terms of size, behaviour, and/or impacts, but the term’s meaning remains ambiguous.ApproachWe sought to resolve ambiguity surrounding the meaning of ‘megafire’ by conducting a structured review of the use and definition of the term in several languages in the peer‐reviewed scientific literature. We collated definitions and descriptions of megafire and identified criteria frequently invoked to define megafire. We recorded the size and location of megafires and mapped them to reveal global variation in the size of fires described as megafires.ResultsWe identified 109 studies that define the term ‘megafire’ or identify a megafire, with the term first appearing in the peer‐reviewed literature in 2005. Seventy‐one (~65%) of these studies attempted to describe or define the term. There was considerable variability in the criteria used to define megafire, although definitions of megafire based on fire size were most common. Megafire size thresholds varied geographically from > 100–100,000 ha, with fires > 10,000 ha the most common size threshold (41%, 18/44 studies). Definitions of megafire were most common from studies led by authors from North America (52%, 37/71). We recorded 137 instances from 84 studies where fires were reported as megafires, the vast majority (94%, 129/137) of which exceed 10,000 ha in size. Megafires occurred in a range of biomes, but were most frequently described in forested biomes (112/137, 82%), and usually described single ignition fires (59% 81/137).ConclusionAs Earth’s climate and ecosystems change, it is important that scientists can communicate trends in the occurrence of larger and more extreme fires with clarity. To overcome ambiguity, we suggest a definition of megafire as fires > 10,000 ha arising from single or multiple related ignition events. We introduce two additional terms – gigafire (> 100,000 ha) and terafire (> 1,000,000 ha) – for fires of an even larger scale than megafires.

Extreme wildfire events (EWE) have significant socioeconomic and environmental impacts, with many concerns about their increasing occurrence under climate change effects. We aimed to generate new climate projections critical for predicting EWE in Europe. Using state-of-the-art climate models, we provided long-term projections of key climatic drivers, such as the Continuous Haines Index (CHI) and FIRE Weather Index (FWI), which assess atmospheric instability and fire danger. Projections were made at both pan-European and Living Lab scales, with daily/montly data from CMIP6-SSP scenarios, offering essential insights for wildfire preparedness and management. The data is presented in NetCDF format. The EU_DATA.zip includes two subfolders: one containing the raw daily model data for various variables, and another with the ensemble means of the models for several indices, over the time period 1995-2014; 2041-2060; 2081-2100. The fwi_daily.zip contains both the FWI and the daily values of the variables needed to calculate the FWI from various CMIP6 models, over the time period 1995-2014; 2041-2060; 2081-2100. The Catalonia_LL_FWI, Aquitane_LL_FWW, Peloponnese_GREECE_LL_FWI, Germany_Netherlands_LL_FWI and Portugal_LL_FWI only include the daily FWI values. The LLs statistical downscaling has been performed to a higher resolution (9km) using ERA5-Land as the reference dataset following the methodology of Varotsos 2023*. Within each folder, there is a NetCD file corresponding to calculated indices and variables, generated under various climate models (five in total) and climatic scenarios (three different scenarios) during different time windows (three periods). Example: Index: FWI Model name: cmcc_esm2 Scenario: ssp2.6 Period: 2081-2100 Resolution: Monthly The file: FWI_cmcc_esm2_2081-2100_ssp26_monthly.nc *Varotsos, K.V., Dandou, A., Papangelis, G. et al. Using a new local high resolution daily gridded dataset for Attica to statistically downscale climate projections. Clim Dyn 60, 2931–2956 (2023). https://doi.org/10.1007/s00382-022-06482-z

The current global change is increasing the occurrence of extraordinary wildfires that overwhelm the suppression capacities, provoking substantial damages, and often resulting in human fatalities and threatening ecosystem integrity. Generating reliable and robust climate projections decisive for extreme wildfire events occurrence in Europe at different scales is of high priority to offer the specific conditions under which wildfires will develop to policymakers and stakeholders, so actions aimed to decrease extreme fire risk, enhance the safety and preparedness of citizens and firefighters are built according to future new conditions. In addition to essential variables such as air temperature and precipitation, this report aims to generate spatial projections and analyze indices such as the Fire Weather Index (FWI) and the continuous atmospheric instability (C-Haines index), both at the pan-European scale and at the living lab scale (in 5 biomes representative FIRE-RES living labs) to allow a better understanding of the future changes in the occurrence of extreme wildfire events. We mobilized climate projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to evaluate new-future (2041-2060) and far-future (2081-2100) weather conditions under three socio-economic pathway scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5). Besides, we also evaluated the accuracy of high-resolution FWI seasonal forecasts on historical records of three Mediterranean Living Labs of the FIRE-RES project. The main temporal and spatial results of both the future projections and seasonal forecasts are discussed, and the generated spatial data is available under the ZENODO repository of the FIRE-RES project. 

Recent studies have explored the use of simple correlative models to project changes in future burnt areas (BAs) around the globe. However, estimates of future fire danger suffer from the critical shortcoming that feedbacks on climate change effects on vegetation are not explicitly included in purely correlative approaches causing potential major unknown biases on BA projections. In a recent application of this approach led by Marco Turco and co-workers in the journal Nature Communications (doi:10.1038/s41467-018-06358-z), a simple correlative model was used to project an increase in future burnt areas for the Mediterranean region. The authors related BAs to regional estimates of cumulative drought surrogates, and later used this relationship to infer changes derived from future climate data. To account for negative climate-vegetation feedback on fire regimes, they used regional variability in the BA–drought relationship. The main assumption behind the approach used was that fire–drought relationships currently measured under a given productivity gradient (i.e., sensitivity of fire activity to dry periods is stronger in cooler/productive sites) can be consistently used to infer new relationships arising in the future. While representing a step forward in acknowledging the pitfalls of current projections of BAs, this short-cut falls short in allowing to account for the key process behind climate–vegetation-fire feedbacks. We argue that a series of mechanisms, ranging from the dynamic nature of fire–drought relationships to the human influences they experience, do not ensure that these relationships are to be maintained in the future with major, overall still unknown, consequences on future fire danger projections. Resolving this challenge will greatly benefit from the development of mechanistic approaches that explicitly consider the processes by which vegetation changes derived from climate influence fire regimes.

Climate regulation strategies based on forest restoration could pose an increase in fire risk, especially under drier and warmer conditions over large regions of Europe, impacting climate, the environment and human health. Climate-smarter options, such as wetlands restoration or recovery of grassland, that provide similar benefits for climate but also develop less flammable landscape is a more suitable option for these regions in Europe and elsewhere facing similar challenges.