Africa: Annual rainy season to occur across parts of western regions through November /update 1

Event

Western Africa's annual rainy season will run through November, bringing an elevated threat of flooding, landslides, and mudslides regionwide. During the rainy season, precipitation associated with the West African Monsoon starts to affect coastal areas in the Gulf of Guinea in April or May before migrating inland toward the Sahel in June. The peak of the rainy season has passed and West Africa has experienced average to above-average rainfall in the 2021 rainy season so far. Forecast models indicate that overall rainfall totals are expected to be below average through the rest of the season, but heavy rainfall and thunderstorms are still likely to occur.

Heavy rain across Benin since mid-September has resulted in at least nine deaths from floods and dozens more from other water-related accidents. The release of water from Nagbeto Dam has flooded several municipalities along the Mono, Oueme, and Niger rivers.

Hazardous Conditions
Heavy downpours, flooding, and landslides could affect business, transport, and utility services in many areas. Localized disruptions could persist well after hazardous events have concluded; floodwaters may take days to subside, and debris from mudslides may take weeks to be cleared. Rural communities and informal settlements often sustain the greatest damage and casualties during such events due to poor infrastructure. The risk of flooding is highest in low-lying communities near watercourses in recognized floodplains. Western Africa has several major rivers and lakes, including the Bandama, Black Volta, Cavalla, Gambia, Niger, Oti, Rokei, Senegal, and White Volta rivers, as well as lakes Aheme and Guiers, that could flood during periods of intense rainfall. Flash floods often pose a threat to communities downstream of major rivers or dams in the event of structural failure. Urban flooding is possible in areas with poorly maintained or inadequate drainage systems, while storm surges may trigger flooding in coastal areas. Landslides and mudslides are possible in hilly and mountainous areas.

Transport
Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas, especially in rural areas, where infrastructure is already of a poor standard. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters.

Severe weather could also exacerbate transport disruptions in areas already hard-hit by the coronavirus disease (COVID-19) pandemic, particularly resulting in air, land, and maritime freight shipment delays. Significant downpours could trigger flight delays and cancellations at any domestic and international airports that are continuing to operate. Authorities may temporarily suspend port operations if strong winds trigger hazardous sea conditions. Flooding could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation.

Localized business disruptions may occur; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.

Health
The threat of disease outbreaks is elevated during the rainy season. Backflow from drains that has mixed with floodwaters can become trapped in open areas when inundations recede. These stagnant pools often become a breeding ground for mosquitoes and bacteria, increasing the incidence of insect- and waterborne diseases. Exposure to contaminated water from inundated industrial sites, sewer systems, and septic tanks also poses a significant health threat.

Advice

Monitor local media for updates and advisories. Confirm all transport reservations (air, ground, and maritime) prior to travel. Make allowances for possible supply chain disruptions throughout the rainy season, particularly in areas affected by flooding and or/landslide events.

Avoid low-lying areas near streams, rivers, and other bodies of water, such as reservoirs and coastlines, due to the threat of flooding. Do not drive on flooded roads. Exercise caution in elevated terrain due to the threat of landslides and mudslides. Charge battery-powered devices when electricity is available; restrict the use of cellphones to emergencies only during periods of severe weather. Take precautions against insect- and waterborne diseases. Keep any necessary medications in a waterproof container.

Resources

National Meteorological Agency of Benin (French)
Ghana Meteorological Agency
Meteo Liberia (French)
National Meteorological Service for Nigeria
Sierra Leone Meteorological Agency Facebook
Meteo Centrale Guinea
Meteo Bissau (Italian)
Senegal National Agency for Civil Aviation and Meteorology (French)