Africa: Annual rainy season likely to cause localized disruptions and increased flood threat throughout Southern Africa through March

Event

The Southern Africa annual rainy season is forecast to bring sustained heavy rainfall across most of the southern part of the continent, including Angola, Zambia, Zimbabwe, Botswana, Namibia, South Africa, Lesotho, and Swaziland (eSwatini), through March 2021. The rainy season is already underway in northern Angola, Lesotho, eSwatini, and eastern South Africa, while the rest of southern Africa will experience an increase in rainfall beginning in November. There are a few exceptions in the region where the rainy season is unlikely to have major impact, including the Northern and Western Cape of South Africa, the desert regions of western Namibia, and the Makgadikgadi Pan Desert of Botswana. The heavy rainfall period will increase the risk of flooding and landslides. Meteorological agencies throughout southern Africa may issue weather warnings in response to the upcoming rainy season, particularly if extreme rainfall, severe thunderstorms, or strong winds are forecast. Overall, near-normal or slightly below-average rainfall is expected this season across southern Africa, except for Angola, which is expected to experience above-average rainfall.

Flood-prone Areas
Communities with poor or a lack of stormwater drainage systems may experience urban flooding during periods of significant rainfall, while areal flooding poses a threat to sites near rivers and streams - particularly those within recognized floodplains. Deadly flash flooding is possible following torrential downpours, especially in vulnerable communities near the edge of watercourses.

Floodwater ponding events might also be a persistent issue in low-lying areas over the coming weeks and months. Even relatively low amounts of precipitation can trigger flood events in areas where dry, compacted soil is unable to absorb runoff. Landslides and mudslides could occur in hilly or mountainous areas, including the Drakensburg (South Africa, Lesotho, and Swaziland) and Witwatersrand Mountains (South Africa and Botswana).

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 trigger flight delays and cancellations at domestic and international airports. Authorities may temporarily suspend port operations or close beaches 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.

Delays to rail transport are also possible, especially for shipments along railway systems near the edge of area watercourses; floating debris and inundated tracks could lead to service suspensions. Localized business disruptions may occur in low-lying areas; 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 on weather conditions. Confirm all transport reservations (air, ground, and maritime) before 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

Botswana Meteorological Service
Eswatini Meteorological Service
Lesotho Meteorological Services
Namibia Meteorological Service
South Africa Weather Service
Zambia Meteorological Department
Zimbabwe Meteorological Services Department