World Weather Attribution scientists say rising greenhouse gas emissions made the nearly 3-year drought at least 100 times more likely.

Ethiopia, Kenya and Somalia have endured five failed consecutive rainy seasons since October 2020, with aid groups labelling it “the worst drought in 40 years”.

But while the drivers behind the drought are complex, a team of international climate scientists with the World Weather Attribution (WWA) group found rising greenhouse gas emissions made it at least 100 times more likely.

“Climate change has made this drought exceptional,” said Joyce Kimutai, a climate scientist with the Kenya Meteorological Department who worked with WWA to tease out climate change’s role. She and her team found that in a 1.2 degrees Celsius (2.2 degrees Fahrenheit) cooler world, the combination of low rainfall and evapotranspiration “would not have led to drought at all”.

Unlike with extreme heat and heavy rainfall, scientists have a harder time pinning down climate change’s contribution to droughts around the world.

Using computer models and climate observations, the WWA team determined climate change had made the Horn of Africa’s long rains from March through May twice as likely to underdeliver, and the short rains from October through December wetter.

But the nearly three-year drought has also coincided with La Nina, an ocean phenomenon resulting from unusually cold water in the equatorial Pacific known to cause below-average short rains in East Africa. This ultimately counteracted the excess moisture added by climate change.

“If you have a doubling of the chance of a severe drought, that really sets the stage for these sequential shocks that have devastated the region,” said climatologist Chris Funk at the University of California, Santa Barbara who was not involved in the analysis.

In addition to less rainfall in the Horn of Africa, a warming climate means more water is evaporating from the soil and transpiring from plants into the atmosphere. Many people affected across the region are pastoralists or farmers who have watched crops wither and water sources run dry.

“This drought is primarily due to the strong increase in evaporative demand caused by high temperatures,” said Kimutai.

Despite initial predictions of a sixth failed rainy season, the region is now receiving some rain, she added.

Although it will take far more rain to help farmers and pastoralists recover, “it’s really positive that we’re seeing rainfall in the region at the moment”, Kimutai said.

The war in Ukraine has affected the humanitarian response, as traditional donors in Europe divert funding for the crisis closer to home.