East Africa floods: How climate change amplifies El Niño fallout

• Floods kill hundreds in Kenya and Tanzania
• Climate change plus El Niño spell double trouble
• Scientists predict more weather chaos ahead

LONDON/NAIROBI - Floods in East Africa have killed hundreds of people as intense downpours submerged towns and villages, washed away crops, and destroyed critical infrastructure such as dams, roads and bridges.

Scientists say a deadly cocktail of man-made climate change mixed with cyclical El Niño weather is behind the catastrophic floods affecting Kenya, Tanzania, Uganda, Burundi, and Somalia - and warn that more weather chaos lies ahead in 2024.

So what is El Niño and how does it interact with climate change?

What is El Niño?

It's what happens when unusually warm surface temperatures in the eastern Pacific Ocean unleash a domino effect on weather patterns right around the globe.

El Niño, which on average happens every 2 to 7 years as part of a natural cycle, lasts 9 to 12 months, a period that began last June and has now ended, according to Australia's Bureau of Meteorology.

This warm spell is followed by a neutral period which could then shift to unusually cold ocean surface temperatures, called La Niña, later this year.

El Niño is a phenomenon distinct from our human-driven climate crisis, said Richard Allan, a climate scientist at the University of Reading, but its impacts will be all the more intense in a warmer atmosphere.

What impacts have El Niño and climate change had?

The effects of the El Niño depend on the region, with some parts of the world forgoing rain while others flood.

The World Meteorological Organization (WMO) says El Niño, alongside a phenomenon called the Indian Ocean Dipole, is behind the deluge in East Africa.

It said planet-heating greenhouse gas emissions were also a major driver.

Researchers from World Weather Attribution (WWA), a global team of scientists that examines the role played by climate change in extreme weather, said this month that recent heatwaves in West Africa would not have happened without climate change and were made still worse by El Niño.

Weather conditions due to El Niño have been the key driver of deadly drought in Zambia, Zimbabwe and other parts of southern Africa, the WWA researchers said in another new report.

But throw in climate change and scientists say the impact is exacerbated.

"Studies have shown that many extreme weather events have been driven by a combination of both climate change and El Niño," said Joyce Kimutai, a researcher at the Grantham Institute at Imperial College London, who worked on the southern Africa report.

For example, the WWA group said climate change was primarily responsible for last year's exceptional Amazon rainforest drought, but El Niño was a contributor as it suppresses rainfall and often leads to droughts in the region.

How has extreme weather affected people and nature?

The extreme weather has taken a toll across the world from Kenya to Australia.

In Kenya, for example, nearly 170 people have died so far from heavy rains and flooding since March, while the death toll in neighbouring Tanzania has reached 155.

More than 185,000 have been forced to leave their homes in Kenya, while hundreds of thousands have also been displaced in Burundi and Tanzania.

Coral reefs have also suffered a fourth global bleaching - stretching from Australia to Mexico - as climate change and El Niño led to record high ocean temperatures, according to the U.S. National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch.

Will 2024 be as hot as last year?

Climate change and El Niño drove average temperatures 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial times in the 12 months to February - a worrying world first that scientists fear could be a harbinger of worse to come.

Keeping warming below 1.5C in the coming decades is seen as crucial to avoiding dangerous tipping points and averting the worst impacts of climate change.

Although the current El Niño has ended, the impacts of the warm ocean on the atmosphere are expected to linger for most of 2024, mirroring the highs of 2023.

The World Meteorological Organization (WMO)'s head of climate monitoring, Omar Baddour, said in March that 2024 was highly likely to set new heat records, as the year after an El Niño event tends to be warmer still.

This article was updated on April 30 as floods killed hundreds of people across East Africa.

(Reporting by Nita Bhalla and Jack Graham; Editing by Lyndsay Griffiths.)