Severe flooding killed more than 800 people in Nigeria, Niger, Chad and neighbouring countries between June and October last year. In Nigeria alone – where the event was called the “most devastating” in a decade – floodwater displaced 1.3 million people and damaged more than a million hectares of farmland.
The World Weather Attribution service finds that climate change made the region’s 2022 rainy season 20% wetter than it would have been without human-caused climate change. The study adds that shorter periods of intense rainfall in the Lower Niger Basin, which worsened the floods, are now about twice as likely to happen because of climate change.
Meanwhile, as countries across West Africa battled with deadly flooding earlier this year, the Sahel – a 5,900km-long band of semi-arid land that stretches across Africa just south of the Sahara – faced a drought-induced food crisis. The region’s 2021 rainy season was shorter and drier than usual. As crop yields fell and food prices rose, food insecurity in the already-vulnerable region took a hit.
A rapid attribution study by the same team finds that “chronic vulnerability” was the main driver of Central Sahel’s “food security crisis”. The authors were unable to find the signal of climate change in the region’s rainfall pattern, due to uncertainties in observational data.
Both studies take place in the context of “extreme vulnerability”, resulting in “massive human consequences”, Maarten van Aalst from the Red Cross Red Crescent Climate Centre told a press briefing.
An early and intense rainy season drove widespread flooding across West Africa this year. More than 800 people were killed over June-October and tens of millions more were displaced. In Nigeria and Niger, the floods were among the deadliest on record.
In Nigeria alone, floodwater inundated hundreds of thousands of hectares of land, displacing 1.3 million people and damaging more than a million hectares of farmland. Among the country’s dead are 76 people who were killed when a boat carrying flood victims capsized.
Chad declared a state of emergency in October, following the heaviest rainfall in 30 years. Meanwhile, in Niger, more than 30,000 homes and shelters, six medical centres, 126 classrooms and 234 grain stores were damaged or destroyed by the floodwater, according to the study.
The flooding was further exacerbated by the release of Cameroon’s Lagdo Dam – part of a river management system that was designed to be accompanied by another dam in Nigeria that has not been completed – the authors study says.
West Africa’s rainy season runs between May and October each year. However, last year, the rains arrived early and were more intense than usual.
Average rainfall over June–September in the Lake Chad catchment (left) and the seasonal maximum of the average seven-day precipitation over June-September in the lower Niger catchment (right). Source: World Weather Attribution (2022).
The rainfall seen over West Africa is “not very rare in today’s climate” – which has already warmed by around 1.2C due to human-caused climate change – according to the study.
The authors find that seasonal rainfall over the Lake Chad Basin has increased “significantly” due to rising global temperatures. In today’s climate, rainfall on this scale is likely to happen once every 10 years in today’s climate, they say.
Meanwhile, the study finds that a seven-day maximum rainfall over the lower Niger Basin is now a one-in-five-year event.
Attribution is a fast-growing field of climate science that aims to identify the “fingerprint” of climate change on extreme-weather events, such as heatwaves and droughts.
To conduct attribution studies, scientists use models to compare the world as it is today to a “counterfactual” world without human-caused climate change. This study aims to distinguish the “signal” of climate change in West African rainfall.
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