Nearly 100 people have been killed and thousands of homes and vital food crops wrecked as floods sweep West Africa.
Aid groups warn the damage threatens to ratchet up the food crisis for millions in the Sahel region, who are already suffering after droughts last year.
The area, south of the Sahara desert, relies on harvests in October which need rain water to grow. But the extra heavy downpours have ruined farmland in Chad and Niger, the countries hardest hit by shortages.
"Rain in the Sahel is much welcome but it needs to be properly distributed over time and over space which is the major issue now," the World Food Programme's Naouar Labidi told Reuters news agency.
In Niger, five thousand people lost their homes and crops when the River Niger burst its banks at the weekend.
And 20,000 more people are at risk of losing their homes if the heavy rains carry on, United Nations officials have warned.
About 30,000 farm animals also died in the flooding and their bodies have been floating near where people collect water, threatening outbreaks of disease.
Meanwhile, on Monday the authorities in Ghana issued a flood warning for three northern regions because of rising water levels at two dams in neighbouring Burkina Faso.
According to the UN's Irin news agency, 40 people have already died in flooding in Ghana in June and July.
In Burkina Faso, the agency reported that 14 people had died last month in floods and many people were sleeping in schools and other public buildings.
Northern Chad in the Sahara desert has recently recorded the heaviest rain in 50 years and hail stones the size of eggs destroyed crops in central Guinea in July, Irin said.
The International Federation of the Red Cross says it is providing aid to flood victims in the Central African Republic and in Ivory Coast, where there have been mudslides.
On Monday, at least 13 people died - most of them children - in the Sierra Leonean capital, Freetown, when a building collapsed during a mudslide, following torrential rain.