The heavy rains that caused catastrophic flooding in South Africa in mid-April were made twice as likely to occur by climate change, scientists said Friday.
An analysis of the flooding, which killed more than 400 people in Durban and surrounding areas in the eastern part of the country, found that the intense two-day storm that caused it had a 1-in-20 chance of occurring in any given year. If the world had not warmed as a result of human-caused emissions of greenhouse gases, the study found, the chances would have been half that, 1 in 40.
The study, by a loose-knit group of climate scientists, meteorologists and disaster experts called World Weather Attribution, is the latest in a string of analyses showing that the damaging effects of global warming, once considered a future problem, have already arrived. And extreme events like this one are expected to increase as warming continues.
“We need to drastically reduce greenhouse gas emissions and adapt to a new reality where floods and heat waves are more intense and damaging,” one of the study’s authors, Izidine Pinto, a climate scientist at the University of Cape Town, said in a statement issued by World Weather Attribution.
The flooding and related mudslides caused more than $1.5 billion in damage and were “the biggest tragedy that we have ever seen,” President Cyril Ramaphosa said at the time. Bridges and roads were destroyed and thousands of homes, many of them in makeshift settlements, were swept away or damaged.
World Weather Attribution conducts its analyses within days or weeks of an event, while it is still fresh in the public’s mind. This one looked at the two-day storm that hit eastern South Africa beginning on April 11 and produced rainfall totals of nearly 14 inches in some areas, half or more of the area’s annual total. The work has yet to be peer-reviewed or published, but it uses methods that have been reviewed previously.
This includes using observational data and two sets of computer simulations, one that models the world as it is, about 2 degrees Fahrenheit (1.1 degrees Celsius) warmer than it was before widespread emissions began in the late 19th century, and a hypothetical world in which global warming never happened.
The finding that the likelihood of such an extreme rain event has increased with global warming is consistent with many other studies of individual events and broader trends. A major reason for the increase is that as the atmosphere warms, it can hold more moisture.
The study noted that from a meteorological perspective, a storm that has a 1-in-20 chance of occurring in any given year, while not common, is hardly a rare event. So the researchers looked at other factors that could have contributed to the disaster’s high toll in deaths and damage.
Among these, they wrote, were legacies of policies instituted during the apartheid era. In 1958, for example, the Durban City Council adopted a measure that forced nonwhites into less desirable and, in many cases, more flood-prone, areas.
The researchers also cited the rise of makeshift settlements as a result of rapid urban growth and a lack of affordable housing. About 22 percent of Durban’s population, or 800,000 people, live in such settlements, which usually lack services and proper infrastructure. In the April flooding, the study noted, about 4,000 of the 13,500 houses that were damaged or destroyed were along riverbanks in these types of settlements, and most of the deaths were in these areas as well.
“Again we are seeing how climate change disproportionately impacts the most vulnerable people, said Friederike Otto, a founder of World Weather Attribution and a climate scientist at Imperial College London.