‘Watershed moment’ – advanced attribution study confirms climate change intensified Durban’s deadly 2022 floods

A new attribution study released on Monday, 29 July, confirms what many have long speculated: the catastrophic Durban floods of April 2022 – which claimed 544 lives and displaced tens of thousands – were made significantly worse by climate change.

“This climate attribution study marks a watershed moment – we now have definitive, scientific evidence of how climate change is impacting us, and more importantly, what we need to plan for,” said Dr Sean O’Donoghue, senior manager of climate change adaptation at eThekwini Municipality.

The research, published in the journal Communications Earth & Environment, is a formal scientific attribution of the event. It shows that rainfall during the storm of 11-12 April 2022 was between 40% and 107% heavier than it would have been in a cooler, pre-industrial climate.

“In every simulation, there was a substantial increase in rainfall due to global warming,” said Professor Francois Engelbrecht, director of the Global Change Institute at Wits University, who led the study. “Even the lowest increase – around 40% – is already a massive jump. In some cases, rainfall more than doubled.”

He explained that in simulations where the storm system made landfall over Durban, rainfall intensified dramatically – similar to the difference between a cyclone skimming the coast and one striking directly.

The April 2022 floods remain the deadliest flood disaster in recorded South African history. More than 500mm of rain fell in just two days in parts of KwaZulu-Natal as measured by weather stations of the Agricultural Research Council. The deluge destroyed homes, infrastructure and livelihoods across the province.

Read more: Early warning systems on floods are not enough; climate crisis literacy saves lives – experts

“Three years after President Cyril Ramaphosa said these floods were part of climate change, science can now confirm he was correct,” said Engelbrecht.

How we know it was climate change

To understand whether the event was intensified by climate change or simply natural variability, researchers used climate attribution modelling. They simulated the storm in two versions of the world: one with today’s levels of greenhouse gases, and one without human emissions. Comparing these worlds helps determine how much more intense or likely the event became due to climate change.

This approach is possible because we know, with precision, how much carbon pollution humans have added to the atmosphere. Since 1750, over 400 billion metric tons of carbon have been released from burning fossil fuels and cement production – half of it since the late 1980s.

As leading attribution scientist Dr Friederike Otto has explained, “We know very well how many greenhouse gases have been put into the atmosphere since the beginning of the Industrial Revolution [thanks to historical emission records and atmospheric measurements].

“So we can remove these greenhouse gases from the atmosphere of climate models and simulate possible weather in the world that might have been without climate change.”

Engelbrecht said that an attribution study consisted of two parts:

“One, the simulation of the actual event – and that’s very similar to the forecast of the event,” he said.

“And then two, the simulation of how that event would have evolved in a pre-industrial world without greenhouse gas emissions.

At its core, he said, the method took the real storm system and “artificially places it in a pre-industrial world not warmed by greenhouse gas emissions” to see how it behaved in comparison.

What makes this study special is its use of “kilometre-scale” climate modelling. Traditional global climate models divide the Earth into large grid boxes up to about 200km wide. At this scale, important small-scale weather features like thunderstorms are too small to model directly, so scientists estimate their effects using statistical assumptions.

But this new model zooms in much closer – dividing the atmosphere into blocks of just one to five kilometres wide – allowing researchers to simulate thunderstorms themselves.

“With kilometre-scale models, we’re resolving the thunderstorms,” explained Engelbrecht. “Instead of approximating them statistically, we now use physics to simulate the updrafts, downdrafts, heat movement and rainfall directly.”

This means the model can better capture the storms that cause flash floods, especially important in South Africa, where most floods come from these convective thunderstorms. This more detailed approach gives scientists a clearer and more reliable picture of how climate change affects extreme local weather.

“That’s a big advantage,” he added. “It gives us more reliable representations of thunderstorms, the rainfall they produce, and the flooding they trigger. In South Africa, the vast majority of flood events are caused by convective rainfall, which comes from thunderstorms.”

The model, powered by the Centre for High Performance Computing in Cape Town, took nearly three years to develop and marks a major step forward for Africa’s capacity to assess climate-driven extremes.

Engelbrecht says the next step is to integrate these tools into disaster planning.

“We need to move from academic modelling to near-operational capability — where we can confirm within days, not years, whether climate change intensified a disaster,” he said.

“With even faster next-generation computers being installed at the CHPC and our newly established modelling system, this is absolutely achievable.”

Crucially, the same high-resolution models used for attribution are also used in forecasting.

“If you want to predict where the flood is going to happen in KwaZulu-Natal two days from now, you need a detailed kilometre-scale short-range weather prediction model,” said Engelbrecht.

“And when you want to understand how climate change made the thunderstorms worse… you also need the same type of model.”

This overlap opens the door to integrating attribution science into real-time early warning systems — helping better protect communities before extreme events strike.

The study found three major drivers behind the storm’s intensified rainfall:

• A warmer atmosphere holding more moisture;
• A warming Agulhas Current increasing ocean evaporation; and
• Changing wind patterns funnelling more moist air into KwaZulu-Natal.

The team also modelled future scenarios, warning that storms in eastern South Africa would probably grow even more intense as the planet continued to warm.

Why KZN is especially vulnerable

KwaZulu-Natal is particularly flood-prone due to geography and climate. “The province has this warm Agulhas Current on its east coast, and it’s been warming over the last four decades,” Engelbrecht explained.

A warmer ocean means more evaporation, and with a warmer atmosphere holding more water vapour, the result is heavier rainfall when storms form. This combination of oceanic and atmospheric warming helped supercharge the 2022 flood event.

East coasts globally face similar risks, Engelbrecht said. “Climate change is increasing flood risks along many of the world’s east coast regions — and ours is no exception.”

Why attribution science matters

Attribution science is central to climate justice — especially in determining responsibility for damages caused by extreme events.

As Engelbrecht explained, attribution science was largely developed to support the study of “loss and damage” – because attribution helps quantify how much worse an event became because of global warming. This evidence is key to accessing international climate finance – like the loss and damage fund – and to holding the biggest polluters accountable.

Read more: COP27 makes history with agreement on ‘loss and damage’ fund for vulnerable countries impacted by climate change

They can also strengthen legal arguments for climate accountability. The recent advisory opinion by the International Court of Justice made clear that countries have legal obligations to cut emissions and protect vulnerable nations.

Read more: Historic ICJ advisory opinion: States must face legal consequences for climate inaction

“I think that the ICJ verdict has just made the attribution science more important,” Engelbrecht said.

Preparing for the next storm

Beyond proving climate’s role in past disasters, attribution studies can help guide adaptation – especially for vulnerable, fast-growing cities such as Durban.

“Once we’ve established scientifically that climate change made a specific event worse, it’s a powerful message for decision makers,” said Engelbrecht.

Before the April 2022 storm, eThekwini Municipality piloted a community-based flood warning system in Quarry Road West informal settlement – and no lives were lost there. 

Read more: ‘It will never be the same’ — life after climate displacement, and why we need to prepare communities

But much more work needs to be done as many communities remain unprepared, and lives of the vulnerable have again been lost in floods this year.

After the 2022 disaster, Durban-based activists, academics and communities co-created the People’s Plan for the Right to Housing in the Age of Climate Change. Integrated into the city’s development strategy, it promotes inclusive governance, localised flood warnings and long-term resilience.

Read more: How a city came together to rewrite its future in the age of climate change

“This kind of research, which makes a clear link between climate change and extreme flooding, is critical,” said Kira Erwin of environmental justice group groundWork. “It helps us really take stock of what we need to start to do in the city of Durban to keep ourselves safe.

Chris Trisos of UCT’s Climate Risk Lab agreed: “We need to invest far more in adapting to heavier rainfall – from flood-proofing infrastructure to restoring river catchments. The 2022 floods are not the new normal. If we keep burning fossil fuels, the hazard will only get worse.” DM