El Niño & La Niña: Weather Impacts Around the World

These maps stand on decades of research into El Niño and La Niña around the world. A hearty list of such studies with comparison:

Temperature and rainfall around the world

• Bjerknes 1969. Matches. He linked El Niño to heavier rain over the warmed central Pacific and to weather far away; here Dec–Feb rain rises about 4 mm/day (+77%) near the date line while the Maritime Continent dries about 11%.
• Horel & Wallace 1981. Matches. They described the Pacific–North American pattern; here Dec–Feb is warm over Alaska and western Canada (+0.6 to +0.9 °C) and slightly cool along the U.S. Gulf Coast.
• Rasmusson & Carpenter 1982. Matches. El Niño warming of the equatorial Pacific builds through the northern summer and autumn and peaks around December; here the Niño-3.4 warming grows from about +0.5 °C in Jun–Aug to +1.0 °C in Dec–Feb.
• Trenberth et al. 2002. Matches. The warm eastern Pacific, the cooler horseshoe in the western Pacific and the warming of Alaska and the tropical Indian Ocean all appear in the El Niño temperature maps.
• Halpert & Ropelewski 1992. Matches. El Niño winters (Dec–Feb) are warm over Canada, Alaska and southern Africa and slightly cool along the U.S. Gulf Coast, as they found.
• Ropelewski & Halpert 1986. Matches. They found wetter Gulf Coast and northern Mexico winters, warm Alaska and western Canada and a cool Gulf Coast in El Niño; here Dec–Feb is about 20% wetter along the Gulf Coast and Florida, 0.6–0.9 °C warmer over Alaska and Canada, and slightly cool (about −0.2 °C) along the Gulf.
• Ropelewski & Halpert 1987. Matches. Their regions of consistent El Niño rainfall show up: drier Indonesia, northern Australia, southern Africa, India and northeast Brazil, and wetter southeast South America (wetter here, though not dotted).
• Ropelewski & Halpert 1989. Matches. La Niña rainfall is broadly the reverse of El Niño in the same regions, as they found.
• Kiladis & Diaz 1989. Consistent. La Niña winters are broadly the reverse of El Niño; here Dec–Feb is −0.3 °C over Canada (El Niño +0.9), −0.4 °C over southern Africa (El Niño +0.6) and −0.18 °C across the tropics (El Niño +0.23).
• Dai & Wigley 2000. Matches. The global El Niño rainfall pattern, wet central and eastern Pacific wrapped by a dry “boomerang” to the west, is reproduced.
• Mason & Goddard 2001. Consistent. They found ENSO reliably shifts the odds of wet or dry seasons in a limited set of regions and seasons; the dotted (significant) rainfall patches here sit in those same places.
• Hoerling et al. 1997. Consistent. El Niño and La Niña are not mirror images; here El Niño’s Dec–Feb rain excess peaks near the date line while La Niña’s deficit sits farther west, the shift they described, and over 5°S–5°N, 170°E–120°W the excess (about +2.9 mm/day) is larger than the deficit (about −1.9).
• Karoly 1989. Consistent. The Pacific–South American wave pattern shows up in Sep–Nov as a warm/cold temperature dipole near the Amundsen and Bellingshausen Seas off West Antarctica, though no box there passes the significance test.
• Mo & Higgins 1998. Consistent. A similar West Antarctic temperature dipole appears in the developing-season El Niño maps, beginning in the southern winter they studied.
• Klein et al. 1999. Matches. Oceans across the tropics warm a few months after an El Niño peaks; here the warming spreads tropics-wide in Mar–May.
• Foster & Rahmstorf 2011. Consistent. Global-mean temperature rises a few months after El Niño and falls after La Niña; here the El Niño − La Niña global difference is about +0.2 °C in Dec–Feb and near zero in the developing summer.
• Thompson et al. 2009. Consistent. Volcanic eruptions cool the globe for a year or two; here the El Chichón (1982) and Pinatubo (1991) eruptions fell in El Niño years and slightly reduce El Niño’s global warmth (by about 0.015 °C).
• Kumar et al. 1999. Consistent. El Niño weakens the Indian summer monsoon, but less so in recent decades; here India’s Jun–Aug rainfall is about 6–8% lower in El Niño years, a modest drop.
• Janicot et al. 1996. Consistent. El Niño tends to dry the African Sahel in its summer rainy season; here Sahel rainfall in July is lower in El Niño years.
• Magaña et al. 1999. Matches. Central America’s summer rains are about 10% lower in El Niño years, deepening the midsummer drought they describe.
• Hendon 2003. Matches. Indonesia’s El Niño drought is strongest in Sep–Nov and fades in the Dec–Feb monsoon, as he found.
• Aldrian & Susanto 2003. Matches. Most of Indonesia dries in El Niño, mostly in the dry and transition seasons rather than the wet monsoon.
• Black et al. 2003. Matches. East Africa’s autumn “short rains” are wetter in El Niño years (about +24% in Sep–Nov).
• Saji et al. 1999. Consistent. The Sep–Nov El Niño rainfall map shows the Indian Ocean Dipole pattern, wetter in the west and drier in the east, which often develops alongside El Niño.
• Hastenrath & Heller 1977. Matches. Northeast Brazil’s Mar–May rainy season is drier in El Niño years and wetter in La Niña years.
• Smith et al. 1998. Partly. They found wetter southern U.S. winters and a drier Pacific Northwest in El Niño; here California, Texas and Florida are about 18–26% wetter in Dec–Feb, but the Pacific Northwest is barely drier (about −2%), likely because its drying is mainly a strong-event signal.
• Brönnimann 2007. Differs. He found a tendency to cold late winters in northern and central Europe after El Niño; here February in Europe is slightly warm and not significant, because the signal is small next to Europe’s large year-to-year swings and four very warm Februaries after El Niño (1995, 1998, 2016, 2024) dominate the average; without them it is slightly cold.
• Ineson & Scaife 2009. Differs. Same as Brönnimann (2007): the cold European late winter they explain does not appear above the noise in this sample of years.

Snowfall

• Smith & O’Brien 2001. Consistent. El Niño winters bring less snow to the Pacific Northwest, northern Rockies and Great Lakes and more to the southern Rockies and, in February, the mid-Atlantic, as they found; the wider Northeast increase they report is not seen here.
• Patten et al. 2003. Matches. Less El Niño snow in the Cascades and around the Great Lakes, more in New Mexico and the southern Rockies.
• Kunkel & Angel 1999. Matches. Less snow across the northern U.S. in El Niño and more in the Southwest, with La Niña broadly reversed.
• Vuille et al. 2000. Consistent. El Niño dries the high Andean Altiplano; here the Altiplano gets less snow in El Niño years.
• Masiokas et al. 2006. Matches. El Niño winters bring deeper snow to the central Andes of Chile and Argentina; here those Andes get more snowfall in Jun–Aug of El Niño years.

Tropical cyclones

• Gray 1984. Matches. El Niño suppresses Atlantic hurricanes; here Atlantic storm-days are about a third fewer, and storm energy (ACE) a little over half, in El Niño years compared with La Niña years.
• Bell & Chelliah 2006. Consistent. The El Niño suppression is strongest in the Caribbean and the Gulf of Mexico (about −45% against the average year) and weaker in the eastern main development region.
• Klotzbach 2011. Matches. Fewer storms reach the Caribbean, the Gulf of Mexico and the Bahamas in El Niño years, where the drop here is largest.
• Kossin et al. 2010. Consistent. El Niño mainly suppresses low-latitude Atlantic storms; here the subtropical central Atlantic is not suppressed in September.
• Chu & Wang 1997. Matches. More storms near Hawaii in El Niño years; here central Pacific storm-days are about three times those of La Niña years.
• Camargo et al. 2008. Matches. Eastern Pacific storms form farther west and are more energetic in El Niño years (ACE about 25% higher here).
• Wang & Chan 2002. Matches. In El Niño years West Pacific typhoons form farther southeast and last longer, with fewer forming in the northwest of the basin; here genesis there is about 22% lower, and about 16% lower over the South China Sea.
• Camargo et al. 2007. Matches. El Niño favors storm formation in the southeast of the West Pacific; here about four times as many storms form at 0–20°N, 150°E–180° in El Niño as in La Niña years (7.0 against 1.6 a year).
• Camargo & Sobel 2005. Matches. West Pacific typhoons are stronger and longer-lived in El Niño years; here ACE is about 1.7 times and intense-storm days about twice those of La Niña years, with similar numbers of storms.
• Basher & Zheng 1995. Matches. South Pacific cyclones shift east, toward French Polynesia, in El Niño years.
• Chand & Walsh 2009. Matches. More South Pacific cyclones form, and farther northeast, in El Niño years.
• Kuleshov et al. 2008. Matches. Fewer cyclones in the Australian region in El Niño years: about 7 a season here against 12 in La Niña years.
• Ramsay et al. 2008. Consistent. They tied fewer Australian-region cyclones to warm Niño-3.4 waters; here fewer form across the region, and storm-days drop most off northwest Australia, while Coral Sea storm-days are not lower as activity shifts east.
• Ho et al. 2006. Partly. ENSO changes where South Indian Ocean storms form and travel more than how many there are; here basin totals barely change and there is only a weak west–east shift, a loose match for a weak signal.
• Girishkumar & Ravichandran 2012. Matches. In Oct–Dec they found Bay of Bengal storms favored in La Niña, with formation shifting west in El Niño; here Bay of Bengal storm-days in Sep–Nov are lower in El Niño years (3.6 against 4.9 in La Niña), while the Arabian Sea is busier (4.0 against 1.1).

U.S. tornadoes, hail and derechos

• Cook & Schaefer 2008. Matches. El Niño winters bring fewer tornado days to the Mid-South and Ohio and Tennessee valleys and more to Florida and the Gulf Coast.
• Cook et al. 2017. Matches. The same Mid-South and Ohio Valley reduction carries into March.
• Allen et al. 2015. Partly. Winter agrees, and spring hail in the southern Plains is still slightly lower after El Niño, as they found; but spring tornado days there are now slightly higher (about +9%) over 1979–2025 because of very active springs after El Niño (2015, 2016, 2019, 2024); for their 1979–2013 period these data show fewer (about −7%).
• Lepore et al. 2017. Partly. As for Allen et al. (2015): spring hail in the southern Plains still agrees in sign, but the tornado signal is reversed in this longer record by a few recent springs.
• Johns & Hirt 1987. Consistent. They found warm-season derechos most frequent from eastern South Dakota to the upper Ohio Valley; the derecho map here peaks in a similar band, from Kansas–Nebraska and Iowa–Illinois toward Ohio.
• Bentley & Mote 1998. Partly. Their main warm-season corridor (1986–95) ran through the southern Plains, and they also found cool-season derechos in the South; this archive peaks farther north (Iowa–Illinois) and lists warm-season events only.
• Coniglio & Stensrud 2004. Matches. The warm-season derecho corridor runs from Kansas and Nebraska through Iowa and Illinois to Ohio.

Data and methods behind the maps

• L’Heureux et al. 2024. Defines the Relative Oceanic Niño Index (RONI), NOAA’s index since 2025, which sets the El Niño and La Niña years here; the year lists match NOAA’s.
• van Oldenborgh et al. 2021. Explains why a relative index is needed as the whole tropics warm, the reason these maps use RONI.
• Capotondi et al. 2015. Events differ in where and when the ocean warming peaks; these maps average over that diversity.
• Deser et al. 2018. With only about 15 events of each kind, composites carry large sampling noise; for example, Canada’s Dec–Feb El Niño warmth is +0.9 °C against all years but +1.7 °C against the 12 neutral years.
• Hersbach et al. 2020. Describes ERA5, the source of the temperature, rainfall and snowfall maps.
• Adler et al. 2003. The ERA5 rainfall climatology here has the same patterns as this satellite–gauge product, running about 5–10% wetter over the tropical oceans, a known ERA5 trait.
• Mitchell & Wallace 1992. The seasonal march of the tropical rain belts they describe, including the eastern Pacific’s double rain belt in spring, is reproduced in the climatology maps.
• Behrangi et al. 2016. High-latitude precipitation and snowfall differ widely between products, so read the polar snowfall maps as approximate.
• Wilks 2016. Shows that box-by-box significance dots often appear by chance and recommends controlling the false discovery rate; the dots here use a stricter whole-map patch test instead.
• Maris & Oostenveld 2007. The cluster permutation test used for the dots, borrowed from brain imaging.