Suffering from rain, Rio Grande do Sul experienced four tragedies in less than a year

The state of Rio Grande do Sul declared a public calamity this Wednesday, 1st, after the heavy rains that hit the region left at least 37 people dead, thousands of people displaced and 134 municipalities suffered some type of damage related to the storms. The disaster is classified as “high intensity” by the decision.

In less than a year, Rio Grande do Sul suffered three other similar rains. In June 2023, the passage of an extratropical cyclone left 16 people dead. The incident repeated itself in September, when 54 deaths were recorded. In November of the same year, a third storm occurred that claimed fatalities.

On three occasions, as well as in the recent storms this week, the Taquari River overflowed its banks and flooded cities close to its banks, such as Lajeado, a municipality about 115 kilometers from Porto Alegre.

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Despite being affected by the four rains, Vale do Taquari is not the only region suffering problems in the state. During the morning of this Friday, the 3rd, the Guaíba River rose 4.61 meters and flooded streets and a bus station in the city of Porto Alegre, according to SEMA (Secretariat for the Environment and Infrastructure) of the state.

In addition, sections of highways were closed and bridges collapsed due to the rain and floods. Storms are a consequence of atmospheric effects such as El Niño, which increases precipitation in southern Brazil.

In the South region, there is an atmospheric blockage that acts as a barrier that prevents the movement of clouds to the Southeast, as explained by Ana Maria Pereira Nunes, post-doctoral student in the Department of Atmospheric Sciences at USP (University of São Paulo). “At the same time, there is the transport of heat and humidity in Rio Grande do Sul, the main ingredient for precipitation”, explains the expert.

Rain frequency

This year’s storms are similar to those observed in 1941, when the state suffered from rains of similar proportions. However, the cities were smaller at the time, as explains Joel Avruch Goldenfum, director of the IPH (Hydraulic Research Institute) at UFRGS (Federal University of Rio Grande do Sul).

In 1941, the municipalities of Vale do Taquari were small villages and, currently, they are cities of 100 thousand inhabitants. “There are many more occupations in areas that would be at risk of flooding, in addition to industrial and agricultural areas, which means that water cannot find permeable surfaces”, says the director of IPH.

Despite this, Goldenfum explains that El Niño and climate change also influence rainfall in the region. “Critical events will be increasingly common, although we need more data to conclude how frequent”, speculates the UFRGS professor. “It doesn’t mean this will happen every year.”

Ana Maria Pereira Nunes points out that climate change provides more energy for the redistribution of heat on the planet, such as clouds and cold fronts. “The Earth system is always seeking balance.”

Flood preparation

With a scenario of rains similar to those currently observed in Rio Grande do Sul, Goldenfum points out that it is necessary for cities to prepare for such events. “We need to work with the population. Many people do not know that they are in risk areas and others believe that it will be a ‘simple flood’”, points out the expert.

For the IPH director, there must be training for the general population and public agents. “From there, we can identify risk areas and determine the most appropriate use. There are regions that could live with flooding, such as parking lots and linear parks that run along the river”, explains Goldenfum, adding that there is no way to reduce the magnitude of climate events, only to reduce their damage.

Furthermore, the UFRGS professor also understands that there are structural measures, such as works that can be used to protect certain areas. “This is possible, although it has limited effects and often resolves that region, but transfers the effect to another place”, says the expert, citing dikes as an example.

*With information from Agência Brasil and Deutsche Welle

**Intern under supervision