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 1800s, and a hypothetical world in which global warming never happened.
The finding that the likelihood of such extreme rainfall has increased with global warming is in line 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 with a 1 in 20 chance of occurring in any given year, while uncommon, is hardly a rare occurrence. So the researchers looked at other factors that could have contributed to the high number of deaths and damage from the disaster.
Among these, they wrote, were legacies of policies instituted during the apartheid era. For example, in 1958 Durban City Council passed a measure that forced non-whites into less desirable and, in many cases, more flood-prone areas.
The researchers also mentioned the rise of makeshift settlements due to 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 amenities and good infrastructure. In the April flood, the study noted, about 4,000 of the 13,500 homes damaged or destroyed along riverbanks were in these types of settlements, with most of the deaths in these areas as well.
“Once again we see how climate change disproportionately affects the most vulnerable people,” said Friederike Otto, founder of World Weather Attribution and climate scientist at Imperial College London.