In Lagos, the most populous city in Nigeria and on the entire continent, streets become rivers during the rainy season as sewage channels and drainage systems are overwhelmed during downpours. The phenomenon is repeated across numerous communities in West Africa, where traffic and business come to a standstill for hours or days, waiting for the streets to drain. Sometimes the flooding becomes deadly.

Last year, hundreds of people were killed in a mudslide in Freetown, Sierra Leone, along a hillside where residents of the booming city had cleared forests to build homes. Victims were buried alive in their houses and vehicles. Environmental groups and local organizations had been warning for years that the development was risky.

In Nigeria, local television stations reported that more than 100 communities had flooded and broadcast images of muddy waters reaching the rooftops of clusters of homes. Some people died when flooding caused their homes to collapse, according to Agence France-Presse.

Local leaders in some areas were advising residents to evacuate. Officials in Anambra State set up 28 camps for fleeing residents. Thousands of people fled their homes in Cross River State, officials there said, noting that many of them lived in swampy areas or along waterways. Farmland was flooded in other states, wiping away crops before they could be harvested.