An exceptionally strong El Niño could contribute to more than 450,000 additional deaths worldwide from extreme heat between June 2026 and February 2027, according to a study by the Climate Impact Lab at the University of Chicago. The estimate is a model-based projection rather than a count of observed deaths, and the effects are expected to vary sharply by region.

The researchers estimate that global land temperatures could rise by 1.2 degrees Celsius during the period, producing 44% more extreme-heat days than in typical years. The mortality risk is projected to be highest across the Global South, where high temperatures can combine with limited access to cooling, health care and other protective infrastructure.

A heavy projected toll in Africa and other regions

The Sahel is projected to record about 66,800 additional deaths, with Nigeria accounting for more than 31,000 of that estimate. Southeast Asia, India and Indonesia are also identified as high-risk areas. Brazil could see about 13,300 additional deaths, according to the study.

Twenty-two climate models indicate that the event will either reach or remain at a “very strong” intensity. Beyond heat-related mortality, the projections point to heightened risks of drought, wildfires and flooding, with possible consequences for food security and local economies. The reported impacts include pressure on tourism in Peru and on agriculture in Paraguay and Argentina.

Regional forecasts show different effects

In Peru, the National Meteorology and Hydrology Service, known as Senamhi, expects October temperatures in some districts of Lima to reach 27°C to 29°C, with warmer-than-usual spring conditions and temperatures of up to 32°C in parts of the country. Senamhi official Yury Escajadillo said some days could feel more like summer than spring, particularly when skies are clear. He also warned that heat would be strongest between midday and 3 p.m.

Peruvian officials are also preparing for short but potentially intense rainfall. Senamhi reported that 38.4 millimeters of rain in Tumbes on Sept. 23 tripled the flow of the Tumbes River within hours. Specialist Raquel Loayza said heavier rainfall could become more likely from November, raising the risk of saturated soils, landslides, flooding and mudflows. She cautioned, however, that some rainfall linked to warm seas is not necessarily caused by El Niño itself.

California and Argentina face contrasting risks

In California, comparisons with the three previous very strong El Niño winters—1982-83, 1997-98 and 2015-16—suggest wetter-than-normal conditions are possible along the central and southern coast. The historical pattern is not conclusive: coastal Southern and Central California received roughly twice the usual rainfall in 1982-83 and 1997-98, while the same areas were drier than average in 2015-16.

Forecasters say the exact position of winter storms and atmospheric rivers remains uncertain. A warm-water pattern in the Indian and western Pacific oceans altered the 2015-16 outcome, while that pattern is not present this year, according to the report. Warmer North Pacific waters could also shift the jet stream south and direct more storms toward Southern California.

Argentina's National Meteorological Service expects above-normal rainfall in the northern Littoral and western Cuyo, as well as wetter conditions in La Pampa, southwestern Buenos Aires province and northeastern Patagonia. It also forecasts lower-than-normal temperatures in parts of the country. The service said El Niño's effects could continue until April 2027, with flooding risks potentially increasing during the summer.