Sérgio R. Leite, Ludimila L. Silva & Luiz R. Gomes


• 76,955 people in shelters; • 1,078 schools affected, totaling 378,000 students; • 240,000 consumer units without electricity and 136,188 customers without water supply; • Six municipalities without telephone and internet services; • 37 federal highways and 49 state highways were completely blocked.


4.1. Considerations on recorded weather events According to a study produced by the World WeatherAttribution[21]


. Rio Grande do Sul is no stranger to


floods due to its largely low-lying physiographic location myriad of river systems, and land-use changes driving vegetation loss. Illustratively, between 2013-2023, it saw 953 emergency decrees due to rain or associated hazards such as landslides[22]


Figure 8. Most of Rio Grande do Sul, Brazil’s southern-most state, has faced damaging floods (Image: Copernicus Program, May 2024)


The study characterized the weather and climate conditions in force between April 26 and May 5, 2024.


The probability and intensity of consecutive heavy rains over periods of ten and four days were assessed, including the relationship with the El Niño phenomenon. According to the authors, the heavy rainfall event was “extremely rare” and is expected to occur once every 100 to 250 years in the current climate. However, without global warming, it would have been even rarer. The article indicates that the probability of these events has increased by a factor of 2, with an increase in intensity of between 6% and 9%. In addition, El Niño played an important role in the event. According to the observations made, for all the data sets analyzed, compared to a neutral El Niño phase, there was a threefold increase in the probability and a 7% increase in the intensity of these events. However, these were not the only floods that Rio Grande do Sul has experienced. In Porto Alegre, as points out, the record of floods is almost as old as the city itself. The first known flood in the


Valente[23]


capital of Rio Grande do Sul dates back to 1795 - just 23 years after the city was founded. Due in part to its location, Porto Alegre has faced major floods in 1873, 1928, 1936, 1941, 1967, and 2023.


166 | Dam Engineering | Vol XXXIII Issue 3


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