Rio Grande do Sul hit by catastrophic flooding
Heavy rainfall brought devastation to the southern states of Brazil in spring 2024, with the worst-hit areas being in Rio Grande do Sul. Over 100 people are known to have died in the floods, with millions affected by the wider effects of the event.
The first flooding was reported on 29 April, when cities such as Porto Alegre swamped by floodwaters caused by heavy rainfall (ITV, 2024).
The UN Refugee Agency was soon warning of a humanitarian crisis in the area, with 107 people known to have died as a result of the floods and 134 missing. In all, 1.7 million people have been affected by issues such as power cuts, water shortages, transportation issues and crop losses, with 41,000 people considered as refugees (UNHCR, 2024).
Event overview and timeline
The origins of the event lay with a high-pressure system over southern Brazil which created an atmospheric block, preventing typical rain-causing systems like extratropical cyclones and cold fronts from moving (MetSul Meteorologia, 2024a). This condition led to unusually high temperatures, up to 10°C above record values, and confined instability and precipitation to the Rio Grande do Sul area (Jornal Estado de Minas, 2024).
The contribution of the ongoing El Niño phase of the El Niño-Southern Oscillation (ENSO) to the meteorological conditions driving the event has been noted by the World Meteorological Organisation (WMO, 2024), among others. ENSO is a phenomenon which strongly influences the ocean temperatures, winds and rainfall patterns of the Pacific Ocean, with the potential to further impact weather in many parts of the world. El Niño phase is characterised by the warming of sea surface temperatures in the central and eastern tropical Pacific Ocean, which slows or reverses the westerly trade winds, bringing warmer water eastwards to the South American coast (Nobre et al., 2019; Lenssen et al., 2020). The warmer water increases evaporation and moisture in the atmosphere in coastal regions of South America, which can result in increased frequency and intensity of rainfall and flooding (Cai et al., 2020).
From 28 April, heavy rain and strong winds affected the northern parts of Rio Grande do Sul, expanding statewide by the next day due to a cold front and a northward moisture flow (MetSul Meteorologia, 2024b). Significant rainfall on 30 April exceeded 150mm in 24 hours in some areas, and early May rainfall in Porto Alegre was nearly three times the average for 1991-2020 (G1, 2024; Sky News, 2024).
More than 200,000 people were displaced due to the floods as rescuers including the army struggled to reach stranded people in Rio Grande do Sul. As per the National Confederation of Municipalities, approximately $1 billion USD has been estimated in economic damages (Financial Times, 2024). As of 6 May, 435,000 customers were without power, with rains affecting 341 towns and cities in the southern Brazilian state (Argus Media, 2024).
The flight services at Porto Alegre’s airport were affected after the Guaiba river overflowed, flooding buildings and runways (BBC, 2024). The agricultural sector also took a hit as soybean fields, livestock farms, and warehouses were submerged by floodwaters. Additionally, rice and soybean production is expected to be impacted by the flooding (MSN, 2024).
Previous flooding in southern Brazil
Southern Brazil has experienced several significant flood events in its history, some of which stand out due to their devastating impacts:
Caraguatatuba, São Paulo, 1967
The flood event in Caraguatatuba is considered one of the deadliest single-day natural disasters in Brazil's history, when a tsunami-like flood of water, mud, and rocks swept through the coastal city, killing between 300 and 500 people. This disaster was marked by intense rainfall, with nearby São Sebastião recording 420mm of rain in one day (ThinkProgress, 2011).
Rio de Janeiro floods and mudslides, 2011
This event was particularly severe in the Serrana Region of Rio de Janeiro, where it caused over 900 deaths. The catastrophe was triggered by extreme rainfall that led to widespread flooding and numerous mudslides. It remains one of the largest weather-related disasters in Brazil, with extensive flooding and landslides severely impacting several towns in the Mountainous Region of Rio de Janeiro (ReliefWeb, 2011). The floods not only caused a devastating loss of life but also significant property damage, estimated at around 2.0 billion reais (approximately $1.2 billion USD; Bloomberg, 2022). This event highlighted the vulnerability of poor communities, as many of the deaths occurred in poverty-stricken areas where living conditions and infrastructure were inadequate when it came to withstanding such a severe natural event (NIBR, 2011).
Rio Grande do Sul, 2020
Heavy rains in July 2020 led to one of the worst floods in recent years, particularly impacting the Taquari Valley region. This event led to two fatalities and forced over 7,000 people to evacuate their homes, widespread destruction of property, and considerable economic losses. (FloodList, 2020).
JBA has nationwide return period flood maps available for Brazil at 30m resolution. For more information about our maps and how they can help you manage your exposure to flood in the country, please get in touch.
This report is accompanied by a flood footprint for the event - detailing extents and depths of the flooding in areas affected. Download it via our Client Portal or request a copy by emailing eventresponse@jbarisk.com.
