Unusually heavy rainfall struck southern Botswana and eastern South Africa from Feb. 16-20, flooding cities and killing at least 31 people. In Botswana, the government said nearly 5,500 people were affected, and more than 2,000 people evacuated.
A new rapid study by the World Weather Attribution (WWA), a team of international climate scientists analyzing extreme weather events, has found that such heavy rainfall events are becoming more likely due to human-induced climate change.
By looking at historical weather observations from the region between southern Botswana and South Africa, the researchers found an increasing trend in very wet five-day rainfall events over the last few decades. The team also estimated that similar five-day rainfall events are about 60% more intense in today’s world, which has warmed by 1.3° Celsius (2.3° Fahrenheit) on average since preindustrial times, before the widespread use of fossil fuels.
The researchers were, however, unable to quantify how much human-induced climate change contributed to the latest February deluge, because the climate models they used produced inconsistent results. “We haven’t been able to quantify the effect, but as the world is warming, we are seeing more extreme rainfall events like this one,” report co-author Ben Clarke, a researcher at the Centre for Environmental Policy at Imperial College London, U.K., told Mongabay in an online briefing.
“Indeed, as our climate continues to warm, it’s understood that this climate is likely to hold more water, and so it’s likely to cause intense rainfall,” said Joyce Kimutai, a climate scientist at Imperial College. This “is likely to overwhelm many systems,” she added, especially drainage infrastructure that hasn’t kept pace with growing populations and rapid urbanization.
For cities like Botswana’s capital, Gaborone, there’s an urgent need to make the infrastructure flood-resilient, said report co-author Piet Kenabatho, an environmental science professor at the University of Botswana.
Simple nature-based solutions can be effective, such as those focusing on absorbing more water into the ground during high flow periods, Kenabatho told Mongabay by email. This can be done by greening bare areas that have lost vegetation due to urbanization, he said, adding that nearly all green spaces in Gaborone have been converted to built-up areas.
But these solutions alone aren’t enough, Kenabatho said. What the city urgently needs is to expand and upgrade its aging stormwater drainage system to quickly channel water out of the city during floods, he added. “Decisions will have to be made as to where some of these waters could be stored.”
Kenabatho said some other African countries use managed aquifer recharge schemes, that channel stormwater into underground aquifers using various methods.
“These concerted efforts will go a long way to improving flood management in Gaborone and similar environments,” he said.
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