The most dangerous stretch of water in the world

Lake Victoria in East Africa is one of the world’s largest freshwater lakes and is used on a daily basis by thousands of fishermen. It is also one of the most dangerous places to fish. According to the International Red Cross, each year thousands of fishermen drown during severe storms.

TU Delft researcher Stef Lhermitte, of the Faculty of Civil Engineering and Geosciences, believes the situation will become worse in the decades to come. “If we do nothing to curb greenhouse gas emissions, by the end of the century superstorms on the lake will occur on average every one and a half years; a tenfold increase.”

Lhermitte was part of a research group that analysed the climatic patterns around Lake Victoria. Its paper ‘Hazardous thunderstorm intensification over Lake Victoria’ was published in Nature Communications on September 23, 2016.

Lake Victoria can be dangerous at night due to the circulation in the atmosphere above the water surface, explains Lhermitte, who was working for KU Leuven (Belgium) during the time of the research. During the daytime, a breeze develops that flows from the cool water towards the warm land. At night, the opposite occurs: the land breeze flows away from the cooling land towards the warmer lake. Since the lake is shaped like a circle, the land breezes converge above the lake. Add evaporation to this cocktail and you get a lot of storms, rain, wind, and waves.

The scientists were able to provide scientific evidence for this pattern in collaboration with American space agency NASA. With satellite images they could map thunderstorms every 15 minutes for a period ranging from 2005 to 2013. To predict the impact of climate change the team also ran climate simulations.

“If we start from a business-as-usual scenario, whereby the emission of greenhouse gasses continues to increase, the extreme amounts of rainfall over Lake Victoria will increase by twice as much as the rainfall over the surrounding land,” said the first author Wim Thiery of the KU Leuven and ETH Zurich in a press release. “As a result, the lake will become a hotspot for night-time storms. Superstorms that only occur once every 15 years today will occur almost every year by the end of the century.”

Lake Victoria directly sustains the livelihood of 30 million people living along its coasts and its fishing industry is a leading natural resource for East African communities. However, given the projected increase in extreme over-lake thunderstorms, the current vulnerability of local fishing communities and their growing exposure driven by rapid urbanisation along the lakefront this lake is likely to remain the most dangerous stretch of water in the world, or so the researchers conclude in their article. The scientists plan to do further research to optimise existing warning systems for local fishermen.

Thiery, W. et al. “Hazardous thunderstorm intensification over Lake Victoria”.Nature Communications. September 23, 2016.