The southern region of Brazil is expected to face increasingly severe climate challenges in the coming decades, with an increase in the frequency and intensity of rains and floods.
This is indicated by a study conducted by the UFRGS Hydraulic Research Institute in partnership with the National Water Agency, published on Tuesday (25). According to research, floods in the region could become up to five times more frequent in 100-year events.
The maximum flow of recurrent floods, which occur in periods of less than ten years, is expected to rise by 14% in Rio Grande do Sul, 17% in Santa Catarina, and 18% in Parana by 2100. According to the researchers, this increase could raise flood levels by up to 3 meters in rivers in mountainous areas, and between 50 centimeters and 1 meter in flat areas.
The increase in frequency and flows represents a challenge for residents of areas that already face almost annual flooding problems, such as the cities on the banks of the Jaqui, Cay and Tacuari rivers, as well as the riparian areas of Porto Alegre.
These areas are still recovering from the effects of last year’s flood, the largest in the history of Rio Grande do Sul.
This tragedy caused the death of 185 people, the loss of 23, and the injury of 806 others. According to the Civil Defense, about 540,000 people have become homeless and 2.3 million have been directly affected, equivalent to one in every five residents of the state.
The study predicts that in Rio Grande do Sul, the maximum flow of floods that are considered rare, those that occur in periods longer than ten years, should increase by 13%.
Despite this growth, the indicator is the lowest in the southern region: Paraná recorded an increase of 25%, and Santa Catarina 17%.
There is also an alert for possible greater flooding in the Itajaí-Aço river basin in Santa Catarina, which runs through regional centers such as Blumenau, Itajaí and Navegantes.
On Sunday (23), a storm in the Itajaí Valley led to 11 municipalities declaring a state of emergency, displacing more than 200 people and damaging more than 360 homes. In Luiz Alves, the worst affected city, the average rainfall forecast for the entire month of November was recorded within 12 hours.
The report also identifies a significant risk to the Uruguay River Basin, which originates on the border with Santa Catarina and flows into the Plate River.
The Uruguay River’s flow is expected to increase by 15% in regular floods and 14% in rare floods, the highest growth among the eight rivers analysed. Solimões comes next with 4.2% and 3.6% respectively. The Amazon, Paraguay, Paraná, São Francisco, Tocantins and Araguaia rivers showed no changes.
Uruguay is also the only river that is expected to record a 7.9% increase in water availability. Decreases reach 23% in Araguaia, 15% in Amazonas, and 12% in Paraná.
Despite the expected increase in flooding, the study also warns of the risk of drought. Even with the expected increase in average annual rainfall – 4.8% in Rio Grande do Sul and 4.7% in Santa Catarina – the duration of the dry period is expected to increase, respectively, by three and five days.
Paraná faces the greatest risk of a water crisis in the southern region, with annual rainfall expected to decrease by 2%, and may face an increase of ten days in the dry period.
“These results highlight significant changes in the hydrological regimes of South American rivers and require adaptation in water resource management and flood forecasting,” says the study organized by researchers Rodrigo Codoro Dias de Paiva, Walter Collichon, Saulo Aires de Souza, and Alexandre Abdullah Araujo.
To produce the forecasts, a hydrological model capable of simulating water flows and flood waves was used, in addition to 28 global climate models (GCMs), and the results reached were compared to the historical period from 1951 to 2014.
However, the text says that the projections have limitations, such as the possibility of underestimating changes due to the low sensitivity of the climate models used, as well as the unpredictability associated with still unknown phenomena.