Assessing the role of compound drought and heatwave events on unprecedented 2020 wildfires in the Pantanal

Abstract

The year 2020 had the most catastrophic fire season over the last two decades in the Pantanal, which led to outstanding environmental impacts. Indeed, much of the Pantanal has been affected by severe dry conditions since 2019, with evidence of the 2020’s drought being the most extreme and widespread ever recorded in the last 70 years. Although it is unquestionable that this mega-drought contributed significantly to the increase of fire risk, so far, the 2020’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 similarly to other areas of the globe, the influence of land-atmosphere feedbacks contributed decisively to the simultaneous occurrence of dry and hot spells (HPs), exacerbating fire risk. The ideal synoptic conditions for strong atmospheric heating and large evaporation rates were present, in particular during the HPs, when the maximum temperature was, on average, 6 ºC above the normal. The short span of the period during those compound drought-heatwave (CDHW) events accounted for 55% of the burned area of 2020. The vulnerability in the northern forested areas was higher than in the other areas, revealing a synergistic effect between fuel availability and weather-hydrological conditions. Accordingly, where fuel is not a limiting factor, fire activity tends to be more modelled by CDHW events. Our work advances beyond an isolated event-level basis towards a compound and cascading natural hazards approach, simultaneously estimating the contribution of drought and heatwaves to fuelling extreme fire outbreaks in the Pantanal such as those in 2020. Thus, these findings are relevant within a broader context, as the driving mechanisms apply across other ecosystems, implying higher flammability conditions and further efforts for monitoring and predicting such extreme events.

Increased Compound Droughts and Heatwaves in a Double Pack in Central Asia

“…Global warming has exacerbated the occurrence of drought and heatwave events [11], especially in North America, Asia, Europe, and Australia. The findings of several recent studies have shown that the frequency and severity of CDHWs are increasing [12][13][14][15]. Moreover, the results indicate that the precipitation trend is the main influencing factor regulating the increase of CDHWs on land, thus highlighting the importance of monitoring regional precipitation trends [16].…”

Typicality of the 2021 Western North America Summer Heatwave

“…The obtained large scale patterns are in good correspondence with those deemed responsible for the dry anomalies leading to persistent drought in the western US. Such agreement is not entirely surprising because, in general, long-term drought increases the probability of occurrence of extreme heatwaves, as a result of the drying of the soil [51], possibly leading to the onset of a cycle of heat, drought, and fire [52,53]. Such mechanisms seem indeed in action and favoured by the ongoing climate change in the western sector of the North American continent, with conditions being and becoming particularly exacerbated in California [54][55][56].…”

Atmospheric Formaldehyde Monitored by TROPOMI Satellite Instrument throughout 2020 over São Paulo State, Brazil

“…It is noted that the summer months presented low concentrations and smaller variance between maximums and minimums, while the situation is opposite in the winter months, with high concentrations and greater dispersion between very concentrated days and less concentrated days. It is also possible to observe that the months of September and October presented the most concentrated HCHO columns, which may be related to the plume of pollution from the fires that occurred in the Brazilian Pantanal in these same months of 2020 [67][68][69]. Some episodes of high concentration can be observed, such as those that occurred on 12 March and 6 October.…”

“…On 28 September, in the episode over the PEMD, the most likely cause was also pyrogenic emission but from fires in the Pantanal and in the Paraguayan Chaco region [68,70]. In Figure 7, it was observed that the HCHO columns with high density are not only over the PEMD but also over the entire west of the state of São Paulo.…”