​Cities need a concrete plan for flash floods

Six people died in Gauteng last week as a result of the province’s flash floods. Some were trapped in cars; others were caught in rivers that had burst their banks.

Infrastructure has been rightly blamed. A growing city means more cement to catch water, but the piping to carry it away has not grown at the same pace. This now costs lives. But it’s a harbinger of things to come, with future climate predictions showing that the drought-flood cycle will become more frequent by 2040.

This is not to say that drought and sudden downpours are not part of South Africa’s climate. As an arid country, with half the rainfall of the world average, events such as El Niño quickly push the country into drought. These are regular and last for about two years, with a handful of large dams ensuring that droughts can be survived. Heavy rain after a drought is normal, something local climate scientists call “amnesia inducing” because it makes people forget the hard lessons learnt from drought.

When this rain falls in the countryside, it is less of a problem because there is natural infrastructure to slow the water down. It soaks into the ground and flooding slows over vegetation and in wetlands. But cities are covered in concrete. When a huge amount of rain falls in a short time, it pools up and takes any path to lower ground. That path could be through a motorway.

Cities build storm water drains to handle large volumes of water. But rapid expansion – with new housing estates, malls and roads constantly being built – in Johannesburg and the rest of Gauteng has outstripped the capacity of these drains. Illegal waste blocking the drains then compounds the problem. So when it does rain heavily, the water has to flow another way.

This is why Johannesburg mayor Herman Mashaba said: “Our city has experienced a flash flood beyond the capacity of our storm water drains.”

The Jukskei River flowing through the Alexandra informal settlement flooded in November 2016. A three-year-old baby has yet to be found.

For now, the city is cleaning out storm water drains and fixing other infrastructure. It’s patching a bigger problem. But its future plans explicitly recognise the danger of the changing climate when it comes to flooding.

Its 2040 Growth and Development Strategy says the city will be “wetter and hotter” in 14 years. This will present problems unique to the Highveld, with coastal cities dealing with the dangers of rising sea levels and storms.

The strategy says Johannesburg’s rainfall will range between 301mm and 758mm a year. That last one is double what it is now. That rain will also come in fewer days, crammed into the months of December, January and February. This will result in “the intensity of rain events, and the possibility of severe rain events, increasing”.

To stop the worst of this, the 2040 strategy says Johannesburg will have to invest in its natural infrastructure. Wetlands will have to be preserved from development and damaged ecosystems brought back to full health. To complement this, built infrastructure such as storm water drains will be extended and rebuilt to handle more water.

This will help the city when catastrophe comes knocking, but will do little to help individuals when the rains do come. Insurance companies have warned of the cost of this future.

In early 2014, late summer rains saw hailstones as big as 7cm in diameter crash down. The average rainfall for the month of March fell in one week. Local insurer Santam received 2 000 claims for hail damage to cars and homes in Gauteng over a 48-hour period. Other insurers said the cost ran into hundreds of millions of rands.

Zimbabwean President Chuma (23) arrived home from work to find all his belongings washed away by the flooding Jukskei River. He was looking for material to build a new shelter. 

The South African Weather Service has said this will become a new normal as these types of summer thunderstorms occur more often.

This prediction is in line with South Africa’s National Climate Change Response White Paper, which says there will be an “increased frequency of heavy rainfall and extreme weather events over most land areas”.

But all of these predictions and plans are based on the Intergovernmental Panel on Climate Change’s middle-of-the-range projections. This United Nations climate body says the world will get between 2°C and 4.8°C hotter this century. The general rule of thumb is to double this warming for Africa’s interior.

New research suggests that even this is a conservative future projection. “Nonlinear climate sensitivity and its implications for future greenhouse gas warming” was published last week in the journal Science Advances. It looked at temperature changes over the past 784 000 years and concluded that the more the world warms, the more rapid that rate of warming. This conclusion has been largely absent from other future warming predictions.

The research said this would probably mean a world that is on average 7°C hotter at the end of this century. In that kind of world, the intricate web of ecosystems that rely on each other to keep life going start to unravel. The rate of change will also be such that most animals are unable to adapt, or move, quickly enough to survive the changes in their local environment.

There is no modelling for what such a rapid change means in South Africa’s interior. 

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Sipho Kings
Sipho Kings is the acting editor-in-chief of the Mail & Guardian

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