La Niña marks the start of summer with irregular rainfall and impacts on the electricity sector.

The summer of 2025/2026 officially begins on December 21st under the influence of the La Niña phenomenon, which, under typical conditions, favors increased rainfall in the Central-North region of the country and contributes to the recovery of river and reservoir flows in the SIN (National Interconnected System).

In this cycle, however, the weather pattern has been marked by irregularities, according to an analysis released by Nottus, a data intelligence and meteorological consulting company for businesses.

The company points to alternating periods of higher rainfall and dry intervals, especially in the central part of the country. Even so, higher rainfall volumes are expected in the Southeast/Central-West, North, and Northeast basins over the next few weeks – which could help consolidate the wet season after an unstable start to the season.

“La Niña favors the formation of the South Atlantic Convergence Zone, responsible for episodes of heavy and persistent rainfall. This pattern usually significantly increases river flow and reservoir levels, but it requires persistence in the location of this rainfall,” said Alexandre Nascimento, managing partner and meteorologist at Nottus.

Impacts on the electricity sector

For the electricity sector, the scenario presents positive signs, but also requires caution. Nottus' presentation indicates that, despite the recent increase in rainfall, flows remain below the historical average in important river basins, which reduces the safety margin for a full recovery of reservoirs throughout the summer.

Nascimento points out that the weak intensity and short duration expected for this La Niña episode reduce the risk of severe droughts in the South of the country, a region that historically suffers from droughts during the phenomenon.

"Years under the influence of La Niña tend to register fewer heat waves, which should maintain milder temperatures in much of the country during the summer," he points out.

On the other hand, the increased frequency of rainfall in the North-Central region raises the risk of extreme events that directly impact the operation of the electrical system. Floods, landslides, rockfalls, and strong winds can cause occasional interruptions in transmission and distribution systems.

"The same rain that helps replenish hydroelectric storage can compromise the sector's infrastructure. It's a delicate balance between benefit and operational impact," notes the meteorologist.

Study conclusions

Nottus' presentation further reinforces that the summer should be marked by a lower incidence of prolonged heat waves, which tends to alleviate peaks in demand for electricity.

Conversely, wind and solar power generation typically experience a seasonal reduction during this period, a behavior considered normal for this time of year, which increases the relevance of hydrological management and thermal dispatch in system planning.

Recent events illustrate this scenario of increased exposure. In the last two months, already under the influence of La Niña, the country recorded tornadoes in Paraná and Santa Catarina, a hailstorm that devastated Erechim (RS), and, on December 10, the passage of an extratropical cyclone that caused floods and gales in the South, Southeast, and Mato Grosso do Sul, leaving almost 2 million consumers without power in the Metropolitan Region of São Paulo.

"It's a series of occurrences that demonstrates the degree of exposure of the electrical system. Even typical phenomena have been manifesting themselves with greater intensity and frequency," Nascimento adds.

Despite the challenges, Nottus assesses that there is no risk of an early end to the rainy season this summer. On the contrary, the trend is for the maintenance of good rainfall volumes in the country's main basins, which may favor the gradual regulation of flows and provide greater predictability to the operation of the SIN (National Interconnected System) in the coming months.

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