Dear Tom,

I’ve been hearing about the major flooding in South Africa. What caused it?

Thanks, Joe Kuczynski Wheaton

Dear Joe,

Last week, the South African city of Durban was hit by nearly a foot of rain that produced massive flooding and landslides, resulting in the tragic deaths of more than 440 people. The rains were not caused by a tropical cyclone, but by a cold core “cut-off low” which produced prolonged periods of heavy rain. This type system is common in South Africa in the fall and spring seasons. Durban experiences some flooding almost every year, but never as severe as this episode. Recent major floods occurred in April 2019 in the wake of 6.5 inches of rain and in October 2017 after a 4.25-inch deluge. Urbanization is increasing rapidly around Durban and the city’s drainage infrastructure has not been able to keep up with the growing demands.