Every year thousands of fishermen in east Africa are killed in boating accidents due to intense night-time thunderstorms that whip up unexpectedly on Lake Victoria. Now a new satellite-based forecast system may help to provide early warnings of the storms.
Lake Victoria, Africa’s largest lake, is the perfect setting for brewing thunderstorms. During the day hot air rises over the land surrounding the lake (in Tanzania, Uganda and Kenya) creating onshore breezes. At night-time the opposite occurs, with air rising over the now warmer lake, pulling air offshore from the cooling land.
“As the lake is shaped like a circle, these land breezes from all directions converge above the lake. Add evaporation to this cocktail and you get a lot of storms, rain, wind, and waves,” explains Wim Thiery, a climate scientist from ETH Zürich.
About 200,000 people fish in the productive waters of the lake and International Red Cross estimates suggest that every year between 3,000 and 5,000 fishermen die because of the violent storms.
Using regular satellite observations taken over the lake, Thiery and his colleagues spotted a strong statistical relationship between certain weather conditions and the probability of a storm. In particular the presence of “overshooting tops” – dome-like protrusions atop cumulonimbus anvil clouds – was associated with intense updrafts.
Writing in the journal Environmental Research Letters, Thiery and colleagues describe the model they have developed. It uses satellite observations to generate storm warnings several hours in advance, and the predictions are publicly available. Now the team is developing an automatic storm warning system, which will be published on Twitter and freely available to all.
