Extreme weather events such as droughts, heat waves and floods have occurred more frequently in various parts of the world and can affect people's food security, economy, culture and physical and mental health (IPCC, 2022). In addition, global warming can interact with social factors, such as population growth and disorderly urbanization, accentuating social inequalities, soil and water degradation, loss of biodiversity and the emergence of pandemics, thus compromising future human well-being (Thornton et al., 2014; IPCC, 2022).

Climate change is a reality in all terrestrial ecosystems, with effects in urban and rural areas (including natural areas), with strong impacts observed in terrestrial and aquatic systems, but also agricultural ones, increasing malnutrition, collective worsening of mental health and climate refugees (IPCC, 2022). The impacts of climate change are different in different regions of the planet, but in Brazil drought and flood events have become more frequent, triggering effects with impacts on agriculture, an increase in diseases, forest fires and burning in deforested areas, in addition to increased frequency of flooding in cities (Marengo et al., 2016). Costa et al. (2022) have projected that these extreme events, including longer sequences of drier days and more concentrated precipitation events, should become more frequent throughout this century even in more moderate emission scenarios such as RCP4.5 and SSP2-4.5.

In Brazil, many instruments have been implemented with the intention of directing adaptation and mitigation actions against the impacts of climate change. These are laws and other devices that seek constant adaptation to the dynamics involved in these processes (Brasil, 2009, 2016). However, the results are still incipient, especially with regard to the effectiveness of actions, as extreme events have become increasingly frequent, affecting a greater number of territories and enhancing environmental, economic and social damage. Freitas et al. (2020) point out that the occurrence of natural disasters in Brazil between the years 2000 and 2015 resulted in economic losses of 4 billion reais (US$ 800 million) in health facilities alone, with the largest cost per event being concentrated in the northern region of the country.

Climate extremes in the Amazon are usually major floods and/or droughts (Marengo et al., 2011; Marengo and Espinoza, 2016). These events have become more frequent and intense in the last two decades, affecting urban and rural regions, and their causes may be related to anomalous heating or cooling of part of the tropical oceans, with emphasis on the El Niño and La Niña phenomena and changes in the South Atlantic Convergence Zone (SACZ). These phenomena can act simultaneously or separately (Brown et al., 2006; Aragão et al., 2007; Zeng et al., 2008; Gloor et al., 2013; Marengo and Espinoza, 2016).

A major challenge in tackling climate change and the resulting extreme events lies in denialism on the part of society (Ferrante and Fearnside, 2021). Not only denial about science, the existence of climate change and human influence, there is also a process of disseminating misinformation throughout society (Diele-Viegas et al., 2021; Bustamante et al., 2023). This situation makes it difficult to build mitigation and adaptation strategies to extreme climate events, which have become more intense and more frequent (Nobre and Borma, 2009; IPCC, 2022).

In the state of Acre, in the southwestern Brazilian Amazon, drought and flood events have been recorded more frequently in recent decades. In 2005, Acre was the epicenter of a severe drought (Zeng et al., 2008; Lewis et al., 2011). In 2015, the state capital (Rio Branco) had the worst flooding that had ever been recorded, with damage estimated between 60–200 million US dollars (Dolman et al., 2018).

Oliveira et al. (2022) identified an intensification in extreme precipitation events and changes in hydrological patterns for the city of Rio Branco and found that the government actions were spotty and limited to the resolution of damage in the short term through declarations of state of emergency or public calamity (see also: Nina and Szlafsstein, 2014; Rocha, 2016). Other extreme events have occurred in the state of Acre over time, but the record of these events is scattered, not showing spatial and/or temporal patterns. The objective of this study is to quantify the frequency of extreme drought and flood events in the state of Acre, in addition to analyzing their causes and impacts.

A total of 254 extreme events were identified between 1987 and 2023, 60% being forest fire and burning in deforested areas, 33% being floods and 6% water crises. On average, six municipalities were affected per year by water crisis, fires or floods (Fig. 2). Up to 2004, an average of one extreme event was recorded per year. After this period, two or more events were recorded in the same year (Fig. 2b). A statistically significant breaking point in the trend was identified by the Pettitt test (p-value = 0.0025) in 2010, and from then on the extremes intensified.

Fig. 2.

Interannual variation of extreme events registered in the state of Acre from 1987 to 2023. (a) Sum of the occurrences of extreme events by municipalities per year and (b) proportional contribution of the occurrence of extreme events.

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Twenty-four municipal or state decrees were identified declaring a state of environmental alert, emergency or public calamity in the analyzed period (Table 2). State government decrees are issued when more than one municipality was affected by an event, and these represent 54% of the decrees issued. Of the decrees issued by municipalities, 54% were made by the municipal government of the state capital - Rio Branco (n = 6), followed by Sena Madureira (n = 3) and Tarauacá and Bujari (both with n = 1). Based only on the publication of the decrees, the most frequent extreme event was flooding (n = 10), followed by water crisis (n = 6) and forest fire (n = 5).

Extreme events in the state of Acre are concentrated in the most populous regions, especially the two most populous: Rio Branco and Cruzeiro do Sul (Fig. 3). In the analyzed period, all municipalities in Acre recorded at least three extreme events. However, the municipalities of Rio Branco and Cruzeiro do Sul recorded 17–26 extreme events, corresponding to one event every two years (Fig. 3a). Flood events were more concentrated in Cruzeiro do Sul, in the western part of the state, registering 19 events (Fig. 3b), while water-crisis events, forest fires and burning in deforested areas are concentrated in the eastern part of the state (Fig. 3c and 3d).

Fig. 3.

Cumulative number of occurrences of extreme events by municipality in the state of Acre from 1987 to 2022. (a) All types of extreme events, (b) flood events, (c) water-crisis events and (d) forest fires, burning in deforested areas and air pollution.

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Climate extremes, floods, droughts and water crises, have intensified, as has been warned by the Intergovernmental Panel on Climate Change (IPCC) reports. Acre may be among the most critical Brazilian states impacted by extreme weather events, however more studies like this must be carried out for all states in the Amazon and Brazil.

Extreme events have been recorded since the 1980s; there was a break point in 2010, after which the number of events increased. The occurrence since 2010 of more than one type of event in the same year in a given municipality may mean the crossing of a tipping point for climate disasters. The large and growing number of extreme weather events in Acre documented here serves as a wake-up call for the Amazon as a whole.

Adaptation and mitigation processes must be considered urgent, not only in the municipalities of Rio Branco and Cruzeiro do Sul, but throughout the state of Acre, especially in the municipalities with greatest social and economic vulnerability.

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Sonaira Souza da Silva reports financial support and article publishing charges were provided by Federal University of Acre.