The impact of compound drought and heatwave events on the unprecedented 2020 fire season in the Pantanal, Brazil

<p>The year of 2020 was characterised by an unprecedented fire season in Pantanal, the largest continuous tropical wetland, located in south-western Brazil. This event was the largest ever recorded over, at least, the last two decades, reaching an amount of 3.9 million ha and affecting 17 million vertebrates^1,2. Recent evidence points out that this event resulted from a complex interplay between human, landscape, and meteorological factors^3,4. Indeed, much of the Pantanal has been affected by severe dry conditions since 2019, with 2020&#8217;s drought being the most extreme and widespread ever recorded in the last 70 years^5,6. The drought condition was maintained at record levels during most of the year of 2021, following the climate change scenarios expected for this region⁷. Prior to this comprehensive assessment, the 2020&#8217;s fire season has been analyzed at the univariate level of a single climate event, not considering the co-occurrence of extreme and persistent temperatures with soil dryness conditions. Here, we show that the influence of land&#8211;atmosphere feedbacks contributed decisively to the simultaneous occurrence of dry and hot spells, exacerbating fire risk. These hot spells, with maximum temperatures 6 &#186;C above-average were associated with the prevalence of the ideal synoptic conditions for strong atmospheric heating, large evaporation rates and precipitation deficits⁴. We stress that more than half of the burned area during the fire season occurred during compound drought-heatwave conditions. The synergistic effect between fuel availability and weather-hydrological conditions was particularly acute in the vulnerable northern forested areas. These findings are relevant for integrated fire management in the Pantanal as well as within a broader context, as the driving mechanisms apply across other ecosystems, implying further efforts for monitoring and predicting such extreme events.</p><p>&#160;</p><p>References</p><p>[1] Garcia, L.C, et al.. Record-breaking wildfires in the world&#8217;s largest continuous tropical wetland: Integrative fire management is urgently needed for both biodiversity and humans. J. Environ. Manage. 2021, 293, 112870.</p><p>[2] Tomas, W. M., et al. Counting the dead: 17 million vertebrates directly killed by the 2020&#8217;s wildfires in the Pantanal wetland, Brazil. Sci. Rep. accepted.</p><p>[3] Libonati, R.; et al. Rescue Brazil&#8217;s burning Pantanal wetlands. Nature. 2020, 588, 217&#8211;219.</p><p>[4] Libonati, R., et al. Assessing the role of compound drought and heatwave events on unprecedented 2020 wildfires in the Pantanal. Environmental Research Letters. 2022, 17, 1.</p><p>[5] Thielen, D., et al. The Pantanal under Siege&#8212;On the Origin, Dynamics and Forecast of the Megadrought Severely Affecting the Largest Wetland in the World. Water. 2021, 13(21), 3034.</p><p>[6] Marengo, J.A., et al. Extreme Drought in the Brazilian Pantanal in 2019&#8211;2020: Characterization, Causes, and Impacts. Front. Water. 2021, 0, 13.</p><p>[7] Gomes, G.D.; et al.. Projections of subcontinental changes in seasonal precipitation over the two major river basins in South America under an extreme climate scenario. Clim. Dyn. 2021, 1-23.</p><p><em>&#160;</em></p><p><em>This work </em><em>was supported by </em><em>Project Rede Pantanal from the Ministry of Science, Technology and Innovations of Brazil (FINEP grant 01.20.0201.00). R.L. was supported by CNPq [grant 305159/2018&#8211;6] and FAPERJ [grant E26/202.714/2019]</em></p>