La Niña produces a wide range of effects across the globe, but its most well-known impact is a distinct split in weather patterns across the United States: wetter and cooler conditions in the north, warmer and drier conditions in the south. This pattern is strongest during the event’s peak intensity, which typically occurs between November and February. La Niña is defined by sea surface temperatures in the central Pacific dropping at least 0.5°C below average for five consecutive overlapping three-month periods, and that cooling reshapes weather systems worldwide.
How La Niña Reshapes U.S. Weather
The clearest effect of La Niña on the United States is a sharp north-south divide in both temperature and precipitation. The northern tier of the country, especially the Pacific Northwest and Great Lakes region, sees wetter-than-average conditions. States like Ohio, Indiana, and Kentucky have the strongest odds of above-normal precipitation. Meanwhile, the Gulf Coast, Texas, the Southeast, and the Four Corners region of the Southwest tend to be drier than normal.
Temperatures follow a similar split. The southern U.S., from the Gulf Coast through the eastern seaboard and up to New England, tends to run warmer than average. The Pacific Northwest through the northern High Plains, by contrast, leans cooler. For the southern states, this combination of warm and dry conditions raises wildfire risk and stresses water supplies. For the northern states, heavier snow and rain can cause flooding and complicate transportation.
More Active Atlantic Hurricane Seasons
La Niña consistently fuels more dangerous Atlantic hurricane seasons. The mechanism is straightforward: during La Niña, high-altitude westerly winds over the Atlantic weaken, reducing wind shear. Wind shear normally tears developing storms apart, so when it drops, more hurricanes form and the ones that do form can grow stronger. The risk to the continental U.S. and the Caribbean increases substantially.
These storms also tend to originate farther east, forming in the deep tropics from weather disturbances that drift off the coast of North Africa. Systems born in that region travel a longer path over warm water, giving them more time and energy to intensify into major hurricanes before making landfall.
Flooding in Southeast Asia and Australia
La Niña pushes the zone of heavy tropical rainfall westward, toward the Maritime Continent (Indonesia, Malaysia, the Philippines) and Australia. The cold water pooling in the central and eastern Pacific shifts deep atmospheric convection, the engine of tropical rain, toward these regions. Low-level winds converge over Southeast Asia and Australia while upper-level winds diverge, creating ideal conditions for heavy, sustained rainfall.
Not all La Niña events produce the same results. Research published in Atmospheric and Oceanic Science Letters found that events centered in the central Pacific trigger significantly more flooding across Southeast Asia and northeastern Australia, with nearly all rainfall increases passing statistical confidence tests. Events centered in the eastern Pacific, by contrast, have little measurable effect on rainfall in these regions. The type of La Niña matters as much as its strength.
Drought in South America
While parts of Asia get drenched, inland South America dries out. La Niña raises drought risk across interior South America by more than 80%, according to research published in Nature analyzing observed streamflow data. Southeastern South America, including key agricultural zones in Argentina and southern Brazil, is especially vulnerable. During the 2020-2023 La Niña, Brazil’s hydropower output dropped to 363 terawatt-hours due to widespread drought, forcing the country to ramp up gas-fired power generation to 87 terawatt-hours to compensate.
Effects on Energy Demand
La Niña’s colder winters in parts of the Northern Hemisphere drive up demand for heating fuel, particularly natural gas. The 2020-2021 winter, shaped by a strong La Niña, produced the highest residential gas consumption in both Europe and North America over a five-year span. Colder temperatures mean furnaces run longer and utility bills climb. In energy markets, this increased demand can tighten supply and push prices higher, especially if the event coincides with other supply disruptions.
Why Some La Niña Events Last for Years
La Niña tends to be stubbornly persistent compared to El Niño. Since 1951, 75% of El Niño events lasted just one year. La Niña is different: only 31% of events were single-year occurrences. Nearly half (46%) lasted two years, and 23% stretched to three consecutive years, producing what scientists call “triple-dip” events. The most recent triple-dip ran from 2020 through early 2023.
Multi-year events compound their effects. Drought-stressed regions don’t get a chance to recover. Reservoir levels in South America drop further each year. Agricultural losses accumulate. The 1998-2001 triple-dip La Niña featured stronger and more persistent subsurface ocean cooling than the more recent 2020-2023 event, though both caused significant global disruptions. A strong El Niño preceding La Niña appears to increase the odds that the cooling phase will persist for multiple years, because the initial El Niño discharges so much heat from the equatorial Pacific that it takes longer for ocean temperatures to return to normal.
Agricultural Disruptions
La Niña’s weather shifts hit global agriculture from multiple directions. Drier conditions in Argentina and southern Brazil threaten soybean and corn yields in two of the world’s largest producing regions. At the same time, excessive rainfall in Australia can delay planting or damage crops at harvest. The offsetting nature of these impacts means global food supply doesn’t always take a uniform hit: when one region suffers, another may benefit. During the 1982 event, for example, Australian wheat production fell 30% while Argentina’s rose 50%.
For the U.S., the drier southern tier can stress winter wheat in the southern Plains, while wetter conditions in the Midwest may benefit or hinder crops depending on timing and severity. Farmers in La Niña-affected regions often adjust planting decisions, crop insurance coverage, and irrigation plans based on seasonal forecasts tied to the event’s expected intensity and duration.
Boost to Pacific Fisheries
Off the western coast of South America, La Niña strengthens the cold-water upwelling that carries nutrients from the deep ocean to the surface. This nutrient-rich water supports massive blooms of phytoplankton, which in turn feed the Peruvian anchovy fishery, the largest single-species fishery in the world. Under favorable conditions, this fishery can yield around 10 million metric tons annually. La Niña years tend to be good years for anchovy catches because the cooler, nutrient-dense water expands the habitat where anchovies thrive. El Niño years, by contrast, suppress upwelling and can devastate the fishery.