Devastating rains that triggered deadly floods in Cameroon, Chad, Niger, Nigeria and Sudan in recent months were worsened by human-caused climate change, a team of international scientists said on Wednesday.

Global warming made the seasonal downpours this year about 5-20% more intense across the Niger and Lake Chad basins, said World Weather Attribution (WWA), a group of scientists studying the link between climate change and extreme weather.

It also said such intense rainfall could occur annually if warming continues.

"Spells of heavy summer rainfall have become the new normal in Sudan, Nigeria, Niger, Cameroon and Chad," said Izidine Pinto, Researcher at the Royal Netherlands Meteorological Institute, in a WWA statement.

This year's floods killed around 1,500 people and displaced over 1-million more in West and Central Africa, according to the UN aid agency OCHA. The rainfall also overwhelmed dams in Nigeria and Sudan.

If global warming reaches 2 degrees Celsius, which could happen as early as the 2050s, such downpours are expected to occur nearly every year in the affected regions, WWA said, calling for more investment in early warning systems and dam upgrades.

"Africa has contributed a tiny amount of carbon emissions globally, but is being hit the hardest by extreme weather," said Joyce Kimutai, researcher at the Centre for Environmental Policy at Imperial College in London.

She said the onus was on this year's COP29 climate talks in November to ensure rich nations contribute "meaningful finance" to help.