'Nothing like the 2024 scenario', says expert about heavy rains in RS; understand why it is different

Despite the disruptions that the storms have caused in several regions of the state, we are not facing an event of the same magnitude as in May last year . This is the assessment of Professor Fernando Fan, from the Hydraulic Research Institute (IPH) at UFRGS, and the Civil Defense of Porto Alegre . However, it requires attention .

The difference begins with the geography of the rain. According to the expert, the rivers overflowed together in 2024, flowing into the Guaíba and raising the lake's level. Now, the scenario is different.

"This time, the heavy rains did not fall in the northern part of the state , they fell precisely in the southern part. So, what is coming towards Porto Alegre are volumes of rain that, in addition to being smaller than what happened in 2024, are only coming from the most central region of the state towards the capital", explains Fan.

In numbers: while, in 2024, 800 millimeters of rain were accumulated in seven days, now the forecasts speak of 100 millimeters in the coming days, comments the professor.

Fan also explains: cities like Santa Maria, Jaguari, Manoel Viana and Alegrete, which were hit by the recent rains, drain their water into rivers like the Ibicuí and Camaquã, which flow into the Uruguai or Lagoa dos Patos — not directly into the Guaíba. This means that the impacts on Porto Alegre will be limited, at least with regard to the lake's level .

The Guaíba is rising, yes. However, according to projections, it should reach between 3.15 and 3.50 meters in the coming days . The so-called “flood level” of the Guaíba is 3.6 meters . In other words: if the worst-case scenario is confirmed, the lake will come close to, but not exceed, the critical mark registered in 2024, according to the Institute of Hydraulic Research.

The Guaíba River is expected to peak between Saturday and Sunday, depending on the rainfall forecast for Thursday and Friday. If it rains more than expected, there could be an additional rise — but the scenario is still far from the 2024 collapse.

Part of the population's anguish is due to the return of water to the streets.

However, as explained by the Civil Defense of Porto Alegre, not all stagnant water is a sign of flooding like the one in 2024 .

"Flooding is what we had in May 2024. We had the Guaíba rising above our doorstep and invading our city. The flooding is the result of this intense rainfall in a short period of time," says Evaldo Rodrigues Jr., executive secretary of the Civil Defense of Porto Alegre.

These floods occur when it rains heavily in a short period of time. They can cause disruption, including for traffic and for residents of more vulnerable areas, but they are different from major floods.

According to the UFRGS professor, the alert at this time is more for those who live in the lower areas of the interior, close to rivers such as the Taquari, Caí, Jacuí and Sinos. With the rains predicted for the next 48 hours, these rivers could reach their flood levels, which means that some homes could be affected, especially in already fragile municipalities.

"Yes, there will be disruption during these days in places that will reach the flood level. Some people will be affected, probably far fewer than in 2024, in these inland rivers," says Fan. "The population that should be most alert is the population affected by the lowest levels," he comments.

The rains that have hit Rio Grande do Sul since Monday (16) have left two people dead, one missing and at least 2,600 homeless , according to the latest update from the state's Civil Defense, on the afternoon of this Wednesday (18).

At least 68 municipalities report flooding, landslides, damage to homes, roads and bridges, in addition to thousands of people displaced or homeless, according to the Civil Defense of Rio Grande do Sul.