“Surprises” is a term introduced to the literature in climate science by Stephen Schneider (1945-2010) to represent unexpected climatic events, usually reflecting processes that are not yet included in climate models (see here and here). These surprises are to be expected because the real-world climate is much more complex than the models, and because the real climate includes chaotic nonlinear processes. Surprises will become more frequent with ongoing global warming, and elements of the catastrophic 2024 flooding in Rio Grande do Sul appear to be an example. Extreme precipitation events in Brazil have increased dramatically in recent years, and they are expected increase much more under projected global warming. Recent indications of disproportional changes include record breaking Amazonian droughts, such as that in 2023 (see here and here), in central and southeastern Brazil as in 2014 and 2021(see here and here) and the 2014 Madeira River flood. The flood disaster in Rio Grande do Sul In April and May 2024, 90% of Brazil’s state of Rio Grande do Sul was flooded, including the capital city of Porto Alegre (Figure 1), displacing 581,638 people, with 169 confirmed deaths and many others missing. Several climatic factors converged to cause such an unprecedented event. The event occurred in an El Niño year, which normally results in greater than average rainfall in southern Brazil, the most famous case being the floods in Blumenau, in the state of Santa Catarina that neighbors Rio Grande do Sul, during the 1982 El Niño. However, in April and…This article was originally published on Mongabay
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