Eighty three people have now been confirmed dead, and more than a hundred are missing, in a series of floods which have swept across Rio Grande do Sul State, Brazil, over the past week. About two thirds of the 497 cities in the state have been affected since the seasonal rains began on Saturday 27 April 2024, with about 115 000 people forced to flee their homes. The worst single incident happened when a hydro-electric dam between the cities of Bento Gonçalves and Cotiporã collapsed, killing more than 30 people.
The flooding is the worst recorded in 150 years of records in Rio Grande do Sul State, exceeding even the floods of 1941, when more than 800 mm of rain fell in parts of the state over a period of 24 days, causing water levels on the Guaíba River to rise by 4.63 m above normal levels in Porto Alegre, the state capital, or 1.63 m above the deck at the city's main port, causing 70 000 people in the city to lose their homes. This year more than 300 mm of rain has fallen in a week, with parts of the state receiving more than 150 mm in under 24 hours, and the Guaíba River has risen by 5.30 m in Porto Alegre.
The flooding is thought to be caused by a combination of a strong el Niño system over the Pacific Ocean, and this years exceptionally strong global temperatures, which are a result of the rising levels of greenhouse gasses (carbon dioxide, methane, and water) within the Earth's atmosphere, a direct result of Human activities, although Brazil is thought to contribute only about 3% of global greenhouse gas emissions.
The el Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of el Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe el Niño conditions, extreme weather conditions a common occurrence.
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