Human fingerprints on Amazon floods: climate change made the 2021 disaster 153% more likely and intensified its socioeconomic impacts

An extreme rainfall event caused historic floods in the western Brazilian Amazon in 2021, with significant socio-economic impacts. Since global climate change is amplifying the frequency and severity of such extreme events, the author's objective was to assess the extent to which this disaster can be attributed to anthropogenic climate change.

To achieve this goal, the authors used CHIRPS data for observational validation of the HadGEM3-A model, which was employed for the attribution analysis, assessed land cover areas directly affected by the floods, and analysed the socioeconomic impacts. The results revealed a positive precipitation anomaly, with rainfall from December to March reaching 48 % above the average (1,329 mm). This extreme event is 153 % more likely to occur in the context of current human-induced climate change than in a natural scenario, with the return period reduced from 107 to 42 years. Furthermore, it was found that the Attributable Risk Fraction (FAR) was 61 %, i.e., the likelihood of such an event occurring can be attributed to anthropogenic influence on climate.

Despite FAR limitations, we estimated that the proportion of climate change-attributable damages amounts to nearly US$10 million and affects over 43,000 individuals directly, likely underestimated. The findings emphasise the urgent need for global climate action. Nationally, multi-sector data collection and climate integration into disaster risk reduction planning are essential for societal adaptation. Public management must include climate change in territorial planning, as environmental preservation and income redistribution can mitigate flood impacts, which tend to be increasingly frequent, as the findings show.