La Niña is back: what it is and what it means for the climate in Latin America

La Niña is back for the second year in a row.

The United States’ National Oceanic and Atmospheric Administration (NOAA) announced Thursday that the climate phenomenon responsible for harsh winters and major droughts around the world has arrived again and will have its effects felt for several months.

According to NOAA, after a period of relative atmospheric equilibrium since the beginning of the year, La Niña will intensify over the next few weeks and will not begin to weaken until spring 2022, which may have an impact on rainfall, the end of the season. hurricanes and the intensity of the coming boreal winter.

“La Niña conditions have developed and they are expected to continue with an 87% probability between December 2021 and February 2022“Said the agency.

According to the statement, experts began to notice that the climatic event was approaching in the last month, when they detected several factors that pointed to its development among them:

  • below-average sea surface temperatures in the equatorial Pacific
  • thermal anomalies in most of the central and eastern Pacific Ocean
  • anomalies in the easterly winds at low levels and in the westerly winds in the upper levels of the atmosphere.

Although generally the signs of its activation begin to be detected in the boreal summer, now, as it happened in 2017, La Niña began to manifest in the fall.

“Our scientists have been tracking the potential development of La Niña since this summer, and it was a factor in the forecast for the above-normal hurricane season that we have seen unfold,” said Mike Halpert, deputy director of the Climate Prediction Center. NOAA.

But what is La Niña and how does it affect the climate of our planet and Latin America?

The girl

To understand what La Niña is, it is necessary to explain the more general phenomenon in which it is encompassed: the so-called ENSO event or El Niño-Southern Oscillation.

El Niño is a weather pattern that causes a weakening of the trade winds in the southern Pacific hemisphere.

Those winds, when they are normal, carry surface waters from the coasts towards the ocean and this causes that the cold waters of the depths arise there.

When El Niño is active, the ocean water in the equatorial zone is warmer.

When El Niño is active, the ocean water in the equatorial zone is warmer.

That cold water is normal in the equatorial zone of the coast of South America.

When these trade winds weaken, this process ceases, the hot water accumulates and there is an increase in the sea surface on the coast of Peru and Ecuador, mainly.

Now, when the trade winds are very strong and the rise of that cold water in the equatorial zone is reinforced and the temperature of the sea is below normal, the phenomenon of The girl, which is a climatic pattern opposite to El Niño conditions.

Generally, between the two phases, a period called “neutral zone”(Which we were in until recently) in which neither event is noticeably active and temperatures are above average.

What are its effects?

The effects of La Niña and El Niño, which range from droughts to floods, from heavy rains to hurricanes, always depend on the area of ​​the oscillation: it can produce droughts in Latin America, heavy snowfalls in the northern United States or droughts in Australia or the Pacific Islands.

And although they follow patterns, this does not imply that each time the conditions are activated they manifest in the same way: no La Niña event is like another.

Although the most accurate forecasts for the current season will be known later this month, NOAA and other meteorological organizations in Latin America foresee “a moderate intensity La Niña“.

This, however, does not by itself predict the conditions in which it will manifest as historical data reveal that there have been more severe droughts in weak or moderate La Niña events than in strong to intense events.

In previous years, the phenomenon has manifested itself very weak, although since 2020 symptoms of a potential strengthening began to be experienced, such as the long Atlantic hurricane season, drought conditions in South America and heavy rains in Central America and the north of South America.

How it will affect Latin America

La Niña generally manifests itself in two totally different forms in Latin America: heavy and abundant rains, increased river flow, and subsequent floods in Colombia, Ecuador, and northern Brazil; and under drought conditions in Peru, Bolivia, southern Brazil, Argentina and Chile.

Several of the latter countries have been experiencing an intense drought since last year, which has affected crops, dried up rivers and impacted hydroelectric generation.

Now there are fears that La Niña will further delay the rainy season in the Southern Cone and make 2022 an even drier year.

Meanwhile, in the northeast of South America landslides have occurred in several countries and in others, such as Colombia, the dams are at 86% capacity, almost double the levels of a year ago, which is historically considered high.

Parana River

Getty Images
The drought has affected several Latin American countries and has “dried up” rivers such as the Paraná.

NOAA has noted that La Niña may influence the final months of the current Atlantic hurricane season, which has been particularly active.

In Mexico, the meteorological authorities indicated that a new activation of the event could translate into an extension of the rainy period until the end of November, as well as intense rainfall in some parts of the country where it is not frequent and later, a drier winter.

In Central America, for its part, the Regional Committee for Hydraulic Resources had predicted since the summer that La Niña could bring to the region “rainier conditions than normal”, mainly on the border of Mexico with Guatemala, southern El Salvador; the central part of Honduras and in the Pacific of Costa Rica and Panama.

The previous La Niña occurred during the winter of 2020-2021 and earlier, between 2017 and 2018.

The last El Niño event took place between 2018 and 2019.

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