Why did it rain so much in Rio Grande do Sul?

Since 2023 we have been seeing intense rains, leading to flooding in the region of the state of Rio Grande do Sul. In April 2024 this scenario intensified into a catastrophe, causing more than a million people to be affected across the state. But Why did it rain so much in Rio Grande do Sul? Was the region caught by surprise with the rains? Here we will analyze studies and the position of scientists specialized in the area to explain how all this culminated in the disaster that Brazil and the world are witnessing.

Explaining the catastrophe

O Rio Grande do Sul is facing an extraordinary weather condition due to thunderstorms and heavy rain. The state is under the impact of successive cold fronts coming from the south of the continent, which found a barrier in the form of a high pressure zone located in the center of Brazil, acting as a big wall which prevents the exit of this cold front.

This same high pressure zone not only blocks the advance of cold fronts, but also diverts moisture from the Atlantic Ocean to Rio Grande do Sul from the East and through the Amazon, entering from the West. As a result, the state is receiving moisture from multiple directions, which contributes to the persistence and intensification of rainfall. Meanwhile, the current cold front stays parked over the region, unable to dissipate due to the influence of the high pressure zone.

The rains that have been ravaging Rio Grande do Sul since the end of April 2024 have left a trail of impact across almost 90% of the state's cities, as indicated by the latest balance released by Civil Defense last Friday morning (10). According to the report, of the 497 cities in Rio Grande do Sul, 435 were affected by the storms, which represents approximately 87,5% of the total. In other words, only 62 municipalities did not record any direct impact related to rain.

The State Government welcomed displaced people and coordinated donations. A sports center in Porto Alegre was transformed into a shelter, while in Canoas another space received around 7.000 people, according to official data. However, obtaining consolidated information was made difficult due to damage to the state database caused by the floods.

The last official balance sheet records 107 deaths, with 1,7 million people affected across the state and almost 330 homeless. More than 800 people are without electricity, and problems with mobile phone networks affect more than 50 cities. Almost 1.000 schools were affected in 239 municipalities, impacting more than 350 students.

An extreme weather event

The expression “socio-environmental catastrophe” gained prominence in the news, while “climate emergency”, "adaptability" e "resilience" become familiar terms for Brazilian authorities and citizens, seeking to understand and face extreme weather events. Brazilian meteorologist Carlos Nobre, a world reference in environmental studies and climate change, clarifies the concept of extreme weather events and why the situation in Rio Grande do Sul was categorized this way.

The professional states that the term refers to meteorological events that have always occurred in nature, such as intense and prolonged rains, severe droughts or heat waves, which are now becoming more frequent and intense. What used to happen every decade now happens every two or even every year, and sometimes still setting new records.

The situation in Rio Grande do Sul exemplifies this, with rainfall that surpasses all previous records. More than 60% of Rio Grande do Sul's territory recorded rainfall volumes exceeding 800 millimeters, something unprecedented. In less than 15 days, it rained the equivalent of five months of precipitation across the state, with more rain forecast due to a new cold front. Although it will not reach the same volume as previous days, river levels will remain high, resulting in continued flooding in lower areas.

This trend is not exclusive to Brazil, and it is occurring all over the world. Extreme weather events are no longer rare, becoming increasingly common due to climate change caused by global warming, a result of the emission of greenhouse gases into the atmosphere.

Other similar events in Brazil that took place in recent years:

• January 2011: rains in the mountainous region of Rio de Janeiro recorded 918 deaths and 100 missing people;
• January 2020: rains in the metropolitan region of Belo Horizonte;
• February 2020: rains in the metropolitan region of São Paulo, Ceasa was flooded, affecting the food supply;
• March 2020: rains on the coast of São Paulo, with an impact on Santos, Cubatão, São Vicente, recorded more than 43 deaths;
• December 2021: rains in southern Bahia left 23 dead;
• January 2022: rain in Belo Horizonte resulted in two deaths;
• January 2022: rains in the metropolitan region of São Paulo recorded 34 deaths;
• February 2022: rains in Petrópolis left 235 deaths;
• March 2022: rains in Petrópolis recorded 7 deaths;
• April 2022: rains in the cities of Costa Verde, Guarapari, Angra dos Reis, in Rio de Janeiro 20 deaths;
• May 2022: rains in the metropolitan region of Recife, 133 deaths;
• December 2022: rains in Minas Gerais left 13 dead;
• February 2023: rains on the coast of São Paulo, in São Sebastião and Ubatuba recorded 65 deaths;
• June 2023: coast of Rio Grande do Sul left 16 deaths;
• September 2023: Vale do Taquari recorded 54 deaths;
• March 2024: rains in the mountainous region of Rio de Janeiro with deaths in Petrópolis and Teresópolis left 8 deaths;
• March 2024: rains in Espírito Santo recorded 18 deaths.

Possible causes

There are many reasons why the state is facing this disaster. Check out some of the reasons why we are witnessing this extreme weather event.

The presence of populations in risk/flooding areas

A insufficient adaptation from cities to climate change can also be attributed to unplanned urban development, which does not always properly consider aspects such as geography and levels of vulnerability in the face of these changes. A environmental preservation often does not receive the necessary attention in this process.

It is not enough to simply relocate the population living in risk areas, it is necessary to consider all regions susceptible to flooding and landslides. Unfortunately, the most valued areas for real estate developments and housing are precisely those most vulnerable to flooding, such as those close to rivers and lakes, or located in flat, low-lying and humid areas.

The wetland ecosystem plays a crucial role in flood mitigation, acting as a kind of “sponge” during these periods of intense rain. Yet these areas are becoming increasingly less resilient due to uncontrolled urban expansion.

With weather forecasts it is possible to announce an extreme weather event days in advance, as Cemaden (National Center for Monitoring and Alerts for Natural Disasters) warned Rio Grande do Sul and the Civil Defense. But we need to make these warning systems everywhere at risk. Cemaden is concluding a study that identifies more than 1,9 municipalities with areas at risk of landslides, floods and flash floods.

Carlos Nobre, meteorologist

From the point of view environmental, urban expansion decisions are going against security, ignoring the environmental risks associated with the occupation of these vulnerable areas. It is essential that there is a more conscious urban planning, which takes into account the preservation of nature and the reduction of the impacts of climate change, aiming at the safety and well-being of urban communities.

Another relevant geographic element of Rio Grande do Sul to take into account when adapting to the new climate reality is the presence of several cities located in river valleys. These areas, characterized by low altitude, are surrounded by elevations such as hills and mountains, and are close to bodies of water.

An example is for Muslim, a city located in the Taquari River Valley, which faced flooding three times during 2023. The first occurred in June, resulting in the loss of 16 lives. In September, 53 people lost their lives due to the passage of an extratropical cyclone, and in November, more than 700 people were affected by torrential rains.

The municipalities of Rio Grande do Sul have been facing strong urban growth over remaining humid areas. These areas are important because they have what we call the sponge effect: this service provided by nature is precisely so that when there is a large load of water it goes there, and the higher areas remain safe. We are doing the opposite of what we should: we are going where we shouldn't go, exposing ourselves to risk, creating situations that put lives in danger, and recurring losses.

Marcelo Dutra da Silva, ecologist, doctor of sciences and professor of Ecology at the Federal University of Rio Grande (FURG)

Worsening by El Niño

To better understand the relationship between El Niño With the rains in Rio Grande do Sul, we must first know the origin and influence of this phenomenon. In the 19th century, fishermen in northern Peru observed an annual flow of warm water from the Pacific Ocean that flowed south. As it happened around Christmas, they called the phenomenon El Niño, a literal translation of "the boy", in honor of the “boy” Jesus.

Peruvian scientists later noted that the most intense phenomenon associated with heated waters it was spaced several years apart and led to catastrophic seasonal flooding on a coastline that was normally arid. The first recorded occurrence of anomalous desert rain was in 1525, when colonizer Francisco Pizarro arrived in Peru.

One of the impacts of this phenomenon is to favor above-average rainfall in the region of the state of Rio Grande do Sul, he explains. Desiree Brandt, executive partner and meteorologist at the company Nottus, specialized in meteorological consultancy for business. Atypical and voluminous rains also affect parts of northern Argentina and southern Paraguay and Uruguay, as the meteorologist explains Leandro cardoso.

Since the last months of 2023, we have witnessed an intense El Niño, after years of a La niña persistent. La Niña is the opposite of El Niño — in it, there is a cooling of the surface waters of the Pacific Ocean. Together, the two phenomena are known as ENSO, an acronym in English for El Niño Southern Oscillation. This oscillation, linked to temperature anomalies, alters global atmospheric circulation patterns, affecting rainfall and temperature regimes.

It is known that a year of El Niño is associated with more rain in the South and dry weather in the Brazilian Northeast. Several of the Northeast's major historic droughts occurred during intense El Niño events. The highest volume of rain in the center-south of the country, therefore, becomes something typical of occurring in this scenario.

Regina Rodrigues, professor of Oceanography and Climate at the Federal University of Santa Catarina, explains that the recent season of extreme rains results from an interaction between El Niño and climate change. Since its emergence in the middle of last year, this climate phenomenon has intensified weather conditions not only in Brazil, but throughout the world.

Before reaching its peak in October 2023, El Niño contributed to extreme temperatures in the country, reaching 40 Graus, triggering drought in the Amazon, forest fires, reduction in the depth of rivers and loss of fauna. A month earlier, Rio Grande do Sul faced flooding due to excessive rain. In just 19 days, rainfall reached 450 mm, well above the historical average for that time, which varies from 70 to 150 mm.

Experts recognize that the early and late stages of El Niño tend to have the most devastating effects. Although some international climate institutes have declared the end of El Niño, there is controversy among climatologists on this issue. Even though the phenomenon has ended in the Pacific Ocean, its effects are still noticeable on the continents.

Lack of preventive measures

The floods that devastated Rio Grande do Sul resulted from the conjunction of an unprecedented climatic event and the negligence of authorities, evidenced by a series of advance warnings that indicated the imminence of a great tragedy.

Before talking about the alerts made, let's get to know the MetSouth, a fundamental piece in this story. MetSul is a meteorology company that provides weather forecasts for the southern region of the country, as well as climate analysis and information on significant weather events. MetSul has gained recognition for its accuracy and detail in forecasts, especially in relation to climate phenomena specific to the south of Brazil and neighboring countries, such as Uruguay and Argentina.

The first signs of intense rain appeared on April 21, with MetSul predicting “consecutive episodes of precipitation in the state, with significant volumes in certain areas“. It was estimated that rainfall could reach up to 200 mm at certain points, between the end of April and the beginning of May.

Four days later, MetSul issued a warning about the risk of a situation similar to that which occurred in 2023. The institute warned that rain could last for several days, reaching up to 300 mm, and exceeding the average expected for two months in just one week. Just like in 2023, a heat wave in the center of the country was diverting moisture southward.

On April 27th, the cities of Canoes, Novo Hamburgo e Porto Alegre the first floods were already registered. Three days later, the mayor of Porto Alegre, Sebastião Melo (MDB), announced the opening of the first shelters in the city, while the first fatalities from the rains were counted and the State Government established a crisis office.

The level of Guaíba river almost increased four meters in just five days, reaching 1,4 meters on the afternoon of April 30th. Above 2 meters, the Guaíba overflows, and this event was already predicted due to the record floods in its tributaries. On May 3, the river reached 4,3 meters, reaching 5,30 meters two days later.

The consequences of the Guaíba flood were immediate. On May 2, the power supply to the five islands of Porto Alegre had to be interrupted. When the previous record of 4,77 meters, recorded in 1941, was surpassed at 21 pm on the 00rd, the capital of Rio Grande do Sul saw its streets flood and the situation collapsed at the end of the week.

The year 2023 served as a warning, with three fatal floods. In June, a cyclone left 16 dead; in September, another similar event caused 54 deaths; and in November, lighter rains resulted in five deaths. The total was 75 fatalities.

Despite these events, investments in flood prevention have not increased substantially. In case of Porto Alegre, data from the Transparency Portal show that the city hall department responsible for the area ended 2023 with R$428,9 million in cash, and investments had been declining since 2021.

Marcio Astrini, executive secretary of the Observatório do Clima (Climate Observatory), highlights that the responsibility for environmental tragedies does not only lie with the state and federal governments, but also with Congress. He points out that the lack of adaptation and combat to climate change are determining factors, areas where the Executives need to intensify their actions and where the Legislature has promoted setbacks.

According to Astrini, the conservative majority in Congress has approved projects considered harmful to the environment, resulting in the dismantling of environmental policies. He highlights that there has never been a period in which Congress was so committed to undoing achievements in this area.

He emphasizes that actions limited to emergency responses are not enough. Extreme events, increasingly common due to climate change, can no longer be seen as unforeseen. A more proactive and comprehensive approach is needed to address these challenges. The expert mentions that deputies are committed to dismantling Brazilian environmental legislation in an incisive way.

In this context, Astrini points to a bill what are you looking for make environmental licensing more flexible. This project would allow states and municipalities to determine which projects would or would not need to undergo an environmental impact analysis, among other measures. This flexibility can increase environmental risks and contribute to the occurrence of more tragedies like those being faced.

The urban planner and professor at UFMG Roberto Andrés emphasizes that preventive measures are essential in situations like this. It highlights the importance of mitigation measures, such as reforestation of river banks to preserve the green belt, which helps reduce water speed and increases infiltration into the soil, reducing the impacts of flooding.

He suggests that all Affected cities must have their own meters for complete monitoring and more robust alert systems. Remove houses from directly flooded areas, especially those in higher risk locations, is also an important measure. The urban planner reinforces that the combination of these environmental protection actions, improvements in monitoring and warning systems can significantly reduce the impacts of extreme events like this.

Regarding the question of a preliminary evacuation plan, he states that it would be viable, but would require a greater investment in security. A plan of this type would require agile real-time monitoring, adequate resources and active civil defense to be effective and save more lives.

The research conducted by Genial/Quaest reveals that the majority of interviewees attribute to the state government, led by Eduardo Leite (PSDB), the greatest responsibility for the climate tragedy in Rio Grande do Sul. Of those interviewed, 68% consider that the state government has a significant portion of responsibility for the calamity, while 20% believe that the responsibility is small and 12% do not attribute any responsibility to the government.

Eduardo Leite's government has faced criticism for its management of the situation, especially considering the changes made to the RS Environmental Code during his first term, in 2019. These changes, which affected around 500 points of the code, were criticized by environmentalists, who considered them harmful to the state's environmental protection system.

Global warming

O global warming, a phenomenon that results in an abnormal increase in the planet’s average temperature due to the intensification of the popularly known “greenhouse effect“, plays a significant role in global climate change. In the specific context of Rio Grande do Sul, Brazil, intense rains are a manifestation of these changes, driven by a series of interconnected climatic factors.

One of these factors is the presence of a dug, an intense wind current, which directly influences meteorological conditions in the region. This trough contributes to weather instability, creating an environment conducive to the formation of intense rain. Furthermore, the humidity corridor coming from the Amazon already mentioned, adds to the scenario, further increasing the quantity and strength of rain in the state.

The influence of global warming interferes with atmospheric dynamics, increasing the energy available for the formation of extreme weather events, such as intense rains. The warmer ocean also plays a crucial role, providing more moisture and heat to fuel these phenomena. Consequently, what could be considered an isolated weather event turns into a catastrophe due to changes in weather patterns, which make meteorological phenomena more extreme and frequent.

Solutions

The announcement of Federal government about the package $ 50,9 billion destined for Rio Grande do Sul reflects a commitment to the recovery and well-being of families, rural workers, companies and municipalities affected by the recent adversity. The measure, sent through a Provisional Measure by President Luiz Inácio Lula da Silva, on May 9, covers a series of vital initiatives:

• Anticipation of social programs: the anticipation of the salary bonus, Bolsa Família and Auxílio-Gás aims to provide immediate assistance to families facing difficulties.
• Priority in income tax refund: prioritizing Income Tax refunds for Gauchos alleviates financial pressures on local taxpayers.
• Additional installments of Unemployment Insurance: The granting of two additional installments of Unemployment Insurance offers crucial support to those who have been affected by economic instability.
• Renegotiations of State debts with the Union: speeding up renegotiations of state debts with the Union seeks to strengthen financial stability and free up resources for essential investments.
• Increase in municipal expenses: Authorization to increase municipal expenditures enables local administrations to respond more effectively to the emergency needs of their communities.
• Release of parliamentary amendments: Release of resources from parliamentary amendments demonstrates a concerted effort to ensure that necessary resources are available where they are needed most.
• Monitoring the situation: installation of a monitoring office in Porto Alegre reflects the continued commitment of federal agencies to closely monitor the situation and coordinate efforts to prevent tragedies and protect lives.

Furthermore, President Lula's commitment to announce a new package of aid next Monday, May 13, highlights the government's determination to provide continued support to Rio Grande do Sul. With an initial contribution of 50 billion reais for reconstruction and economic recovery, the objective is to mitigate the devastating impacts of rains and floods, restoring hope and dignity to the people of Rio Grande do Sul.

How long will it rain?

Marcelo Seluchi, meteorologist and general coordinator of Operations and Modeling at the National Center for Natural Disaster Monitoring and Alerts (Cemaden), predicts that the storms will persist in the coming days due to a phenomenon called the blocking system, which is occurring in the Pacific Ocean and is exerting influence over Brazil. This stagnant atmospheric system tends to last for days, as explained by the meteorologist.

According to the forecast, the rains will continue a little beyond the first decade of May, however will begin to gradually weaken. Seluchi notes that the weather fronts may fluctuate, heading towards the south of the continent, towards Uruguay, or advancing towards Santa Catarina. As a result, it is expected that rainfall will become less intense and there will be longer periods without precipitation.

These cold fronts come from Argentina, arrive quickly in the South Region and are unable to advance. We have a succession of cold fronts that have become stationary and are maintaining the rain for several days.

Marcelo Seluchi, meteorologist and general coordinator of Operations and Modeling at the National Center for Natural Disaster Monitoring and Alerts (Cemaden)

And the future?

Data presented in Global Risks Report 2024, released by the World Economic Forum, cast a shadow over the future. This year, environmental risks may reach a critical point, beyond which it may be impossible to reverse the damage. The report, based on a Global Risk Perception Survey (GPS), reveals that 66% of respondents identify extreme weather conditions as the biggest potential risk to trigger a material crisis on a global scale in 2024.

Faced with this alarming scenario, the Minister of the Environment, Marina Silva, defends the urgent need to establish a state of “permanent climate emergency”. This measure would allow Brazilian municipalities at risk to adopt a more proactive stance in preventing tragedies and protecting their populations and natural resources.

It appears from the studies presented, scientists interviewed and the local history itself, these rains are not isolated cases and should happen again in the region of the state in the coming years (or months), especially when we take into account the anthropocene — scenario in which man interferes in the geography of that location and consequently in the environment, altering them. Public environmental policies must be reinforced to minimize these advances.

To learn more, watch the video on our YouTube channel:

See also:

https://www.showmetech.com.br/como-fazer-doacoes-para-o-rio-grande-do-sul

How to do donations protocols for Rio Grande do Sul in a safe way.

With information CNN [1] e [2], Agência Brasil [1], [2] e [3], Veja e UOL.

Text proofread by: Pedro Bomfim