Southern Brazil has seen an increase of up to 30% in average annual rainfall over the last three decades

Rainfall patterns have changed over recent decades in Brazil. While average annual rainfall has increased in parts of the country, other regions are going in the opposite direction. Such changes have resulted in extreme weather events that are influenced by two important indicators: consecutive dry days (CDD) and maximum precipitation over 5 days (RX5day). The survey conducted by the National Institute for Space Research (INPE), at the request of the Ministry of Science, Technology, and Innovation (MCTI), examines changes in the Brazilian climate over the last 60 years and provides essential information for the preparation of Plan Climate. The data is key for the formulation of effective climate change adaptation strategies and may help the development of municipal, state and regional risk management planning.

"Looking at long-term data trends is crucial because it allows us to identify consistent patterns and gradual changes in the climate, which are often too subtle over short periods of time. This is especially important in a context of climate change, where changes in precipitation can have profound impacts on strategic sectors of society, for example, agriculture and water resources," says Inpe climatologist and researcher Lincoln Alves, who is responsible for the study.

The changes observed vary regionally. According to Alves, each region has a specific climate, influenced by altitude, latitude, vegetation, relief, proximity to bodies of water and other factors. “These climatic peculiarities contribute to variations in characteristics and precipitation patterns observed throughout the country," explains the researcher.

Data collected over the last six decades by the National Meteorological Institute (Inmet) help quantify how much the climate has changed throughout Brazil from 1961 to 2020, considering the first 30 years as the reference period, i.e., the comparative base. Later decades were segmented into three periods: 1991-2000, 2001-2010 and 2011-2020.

Results – Accumulated precipitation anomalies have been observed over the three decades under study. Two contrasting regions stand out in the most recent period (2011 to 2020). The results indicate that the southern states and part of the states of São Paulo and Mato Grosso do Sul have seen an increase in precipitation volumes. During the reference period, the annual average was 1,500 mm, but in the most recent decade, between 2011 and 2020, the volume reached 1,660 mm per year, indicating an increase of between 10% and 30%, depending on the region. According to the series trend map, some specific areas in the north of the country also showed an increase in rainfall.

According to the researcher, the 160 mm increase in annual average rainfall indicates that the region may be more susceptible to disasters due to the intensification of rainfall. "Events like this tend to be enhanced by climate change, becoming even more intense and frequent," he says.

Increased rainfall is associated with the occurrence of extreme rainfall events. The RX5day indicator shows the highest amount of rainfall recorded in a consecutive five-day period. The index is useful for identifying trends in changes in extreme rainfall patterns, which is important for planning infrastructure, flood risk management and flooding. "In other words, the index tells us what the most intense rainfall peak was in a short period of time during the year, helping us to understand how extreme rainfall events can be in a given region," he explains.

According to Alves, analysis of the RX5day index shows a worrisome trend. Comparing the reference period with the most recent decade, the study identified a 20mm increase in the index. "This increase is not an isolated event, but part of a broader trend observed in recent decades, especially in the southern region of the country. Increases in the frequency and intensity of these extreme events, such as the one we are seeing now, require a reassessment of adaptation strategies," he says.

The South is highlighted in the indicator for maximum rainfall in five days between 2011 and 2020. In the graph on the right, the blue line indicates the reference period (1961-1990) and the red line the most recent decade (2011-2020).

Opposite path – While part of the country is getting more rainfall, other regions have faced a downward trend in the average rate of precipitation. Rainfall drops between 10% and 40% have been recorded in hinterland regions of Northeast, Southeast and Central Brazil. The area with the most significant reduction is indicated on the map in yellow and orange.

During the reference period, the average accumulated rainfall was around 1,210 mm. The volume fell in the following decades, dropping to 1,030 mm in the 2011-2020 period.

According to Alves, the reduction of up to 40% in accumulated rainfall in some areas of Brazil is significant and could lead to "a series of worrying impacts". "If this rate continues, we could see a worsening of what we are already seeing: droughts in the Amazon and an even more arid Northeast, which directly affects populations and ecosystems," he says. The researcher also points out that the decrease in rainfall could result in increasingly prolonged periods of drought, which directly affects the availability of water for human consumption, agriculture and industrial activities. "It could lead to food shortages and loss of income for local farmers," he says.

Water scarcity can trigger conflicts over access to water, increase social and economic inequalities and generate public health problems.

According to Alves, rainfall reduction in Central Brazil could lead to more severe and frequent droughts, which could threaten water availability for human consumption and agriculture, especially in the Cerrado region, which is an important agricultural hub. "In the long run, this could not only affect food security, but also raise food and energy prices," he says.

Adaptation – Alves stresses that climate evidence points to the need of integrating risk management into public plans and policies. "This means adapting strategies at all levels of government, local, state, regional and national. Not only responding to ongoing changes, but also preparing communities for future challenges," he explains.

Climate changes observed in Brazil are part of a global trend. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) highlights that climate change is already affecting extreme weather events in all regions of the planet. "Incorporating climate resilience into agriculture, infrastructure, public health and other critical sectors is essential to protecting the economy, the ecosystems and, above all, people's well-being," he concludes.

About the study - Climate information is part of the scientific basis provided by the MCTI to support discussions on updating the Climate Adaptation Plan. Understanding these changes is key to evaluating the climate threat and, consequently, analyzing the possible impacts, vulnerabilities and necessary adaptation. A similar exercise was carried out for Brazil's Fourth National Communication to the Climate Convention.

In addition to precipitation, the maximum temperature indicator and three climate extremes indices were observed: consecutive dry days (CDD), maximum precipitation in 5 days (RX5day) and heat waves (WSDI).


From: Ministry of Science, Technology and Innovation