Why El Niño favours wet short rains in Kenya and drought in southern Africa

Why does the same El Niño tend to bring heavy rain to Kenya in the October–December short rains and drought to southern Africa? El Niño, a warming of the tropical Pacific, moves the places where air rises and sinks across the tropics, and the change reaches the two regions with opposite signs. A western Indian Ocean warmer than its eastern side, known as a positive Indian Ocean Dipole, adds to the rain on the East African side. Both are tendencies, not rules.

The World Meteorological Organization (WMO) said on 8 October 2026 that the Niño 3.4 index, a gauge of Pacific warming, is forecast at about +3.7°C for October–December, peaking around December, against a 1993–2009 baseline. The previous record was +2.6°C in November 2015–January 2016. The same release said wetter-than-normal conditions are more likely across the Greater Horn of Africa, and that a positive Indian Ocean Dipole is expected to peak in October, with an October–December anomaly of about +0.5°C.

The outlook of the Southern African Development Community (SADC) points the other way for the south. It predicts below-normal rainfall across much of the central and southern parts of the SADC region in the 2026/27 rainy season, with above-average temperatures and a higher drought risk, though some northern and northeastern areas may turn wetter, Xinhua reported on 20 October. A SADC disaster-preparedness workshop opened in Johannesburg on 20 October and runs to 23 October.

The link runs through the Walker circulation, a loop of air along the equator that rises over the warm western Pacific and sinks over the eastern Pacific. Tom Di Liberto wrote on NOAA’s Climate.gov in 2014 that in El Niño the warm pool in the western Pacific moves east and the rising branch of the loop follows it. Over the Maritime Continent in the west, he wrote, ‘upward flow weakens, and anomalous sinking motion occurs’, while ‘increased rising motion enhances rainfall over the central Pacific Ocean’. Rising air makes rain; sinking air does not, so the rain moves with the rising air. He added that rainfall also increases over parts of equatorial eastern Africa.

A 2021 paper in Scientific Reports, combining climate-model experiments with observed records, starts from the pattern itself: ‘El Niño events cause droughts in southern Africa and enhanced precipitation and corresponding floods in eastern Africa.’ In the authors’ Pacific-forced experiments the weakened Walker circulation leaves a region of sinking air whose edge reaches the African continent, which cut December–February rainfall over Tanzania. The paper also reports the observed split in December–February: positive rainfall anomalies over the Horn of Africa and negative ones over southern Africa.

The dipole is the second ingredient. Nat Johnson wrote on Climate.gov in 2020 that in a positive phase the water near Java and Sumatra is cooler than normal and the western tropical Indian Ocean warmer. He called ENSO, the El Niño–La Niña cycle, ‘one of the main triggers’ of such events, and said positive events typically bring ‘floods to eastern Africa’. NOAA’s Climate Prediction Center says the positive phase tends to increase rainfall in equatorial East Africa.

In an October 2023 special report on that year’s El Niño, the IGAD Climate Prediction and Applications Centre (ICPAC) said a positive dipole can often occur alongside El Niño and make wet outcomes more likely. It named eastern Kenya, Somalia and southeastern Ethiopia as areas with higher chances of highly above-average rain.

A 2025 review in Nature Reviews Earth & Environment, by Wenju Cai and nine co-authors, reports a strong dipole in anomalies between eastern and southern Africa in October–December, the short rains, linked to interactions with the Indian Ocean Dipole. These links tend to be most pronounced for East Pacific El Niño events, it says.

Strength alone does not settle the outcome. WMO said on 3 September 2026 that the strength of an El Niño ‘alone does not determine how severe its impacts will be’, and that a positive dipole, with a warm equatorial Atlantic, may reinforce, weaken or alter typical El Niño impacts in different regions.

The Kenya Meteorological Service Authority (KMSA), formerly the Kenya Meteorological Department, said in its 2026 short-rains outlook, issued on 26 August, that above-average rainfall is expected across much of the country, including Nairobi, where the rains are expected to start in the second to third week of October. The ongoing strong El Niño also enhances rainfall when it coincides with a positive dipole, the authority said.

WMO’s 8 October release says its rainfall outlooks ‘are not a substitute for national and local forecasts’.