The United States National Oceanic and Atmospheric Administration has made official the return of La Niña, with conditions already present in the tropical Pacific and signs that fit with an episode weak and short-livedThe key reference point is around the -0,5°C threshold in the Niño 3.4 region, a landmark that defines the beginning of the cold phase of ENSO.
After several weeks with flashing signals cooling, the pattern has consolidated and is expected to continue from December to February, with a probability greater than 50%. This scenario could translate into changes in rainfall and temperature in South America, with special attention to southern Brazil and Uruguay, and close monitoring in Argentina.
What is happening in the equatorial Pacific
The sea surface temperature anomaly in the Niño 3.4 region is around -0,5 ° C, placing the system at the limit of a weak Niña. The cooling is concentrated in the central-eastern Pacific, while the trade winds More intense waves push warm waters westward and encourage cold waters to rise in the east. This coupling reinforces the Walker circulation and modulates precipitation patterns on a planetary scale.
Expected duration and evolution of the episode
Most likely regional impacts
In Brazil, the cooling of the Pacific often translates in Rio Grande do Sul as critical area due to the deficit in the south, while the north and northeast tend to register higher rainfall to the average. In addition, the frequency of cold air incursions, with the possibility of more marked outbreaks at the end of the first year of the episode.
Uruguay would face a scenario of rainfall below normal in the final stretch of the year, with potential impacts on the border departments with southern Brazil and the need to adjust water management in urban and rural systems.
In Argentina, the panorama appears heterogeneous According to national agencies: the coast and northeast could see below-normal rainfall; the northwest would have above-average rainfall; the central region would move close to typical values, and the Patagonia would show a bias between normal and lower. The ocean-atmosphere coupling, key to finish defining the signal.
Impacts on the countryside and ecosystems
La Niña can put pressure on production wheat, soybeans and corn due to the lack of water in critical stages, with lower potential yield, more pressure on irrigation and greater vulnerability financial for medium and small producers.
El water deficit increases the danger of forest fires by turning dry vegetation into fuel, and late frosts can complicate fruit and wine growing in areas sensitive to cold outbreaks.
Ecosystems are also affected: the reduction of flows in rivers and wetlands limits habitats, compromises biodiversity and affects the water supply for populations and economic activities.
What signs to watch for and how to prepare
It is advisable to closely monitor the evolution of Child 3.4, trade winds and the Walker circulation, in addition to the ocean-atmosphere coupling. Decision-making benefits from seasonal forecasts, flexible irrigation plans, climate-indexed insurance, and public-private coordination in risk management.
With the cold phase already activated, everything points to an episode short and low intensity but with palpable effects in the Southern Cone: less rain in southern Brazil and Uruguay, and a uneven behavior In Argentina, continued monitoring and adjusting planning will be key to weathering the season with the least possible exposure.
