Recent rain in Western Cape as high as Laingsburg disaster of 1981: expert

The fact that SA’s weather appears to be becoming more unpredictable and intense is indicative of a climate crisis situation, because a warmer atmosphere is more active.

That’s according to Peter Johnston, a climatologist at the Climate System Analysis Group at the University of Cape Town, in the wake of extremely heavy rainfall across parts of the country so far this festive season.

In Gauteng, calls to declare a state of disaster followed hot on the heels of floods that wreaked havoc across the province, leaving communities displaced and affected infrastructure in tatters.

Thunderstorms in the Western Cape a week ago brought as much rain as the flash floods in Laingsburg in 1981, with up to 100mm falling in a few hours.

The Laingsburg disaster, just like the recent unseasonal rain in the province, was caused by a cut-off low, with intense rain and rapid, concentrated run-off, and killed 102 people while washing away all but 21 buildings in the small Karoo town.

Hannelee Doubell from the SA Weather Services said record-breaking rain was recorded at the Paarl and Wellington weather stations a week ago. 

Over 48-hours, Paarl measured 65.2mm and Wellington 59mm. 

Heavy downpours in KwaZulu-Natal also sparked fears of more flooding reminiscent of earlier this year. Johnston cautioned against ascribing a single change in patterns — like unseasonal rainfall — to climate change,but “the likelihood of an extreme event certainly increases as the climate changes”.

The summer rains came late this year in Gauteng and has been much more intense, so we might find that the same amount of rainfall [or more] occurs but over a much shorter period amid intense thunderstorms.

—  Climatologist Peter Johnston

For example, says Johnston, large hailstones “have always been around but the circumstances are going to be right for those big hailstones more often if 35ºC days become more common in Gauteng”.

Speaking on the Western Cape, Johnson said over the past two decades climate change models have suggested three things.

First, it is definitely going to get hotter, increasing by an average of one to three degrees by end of the century.

Second, winter rain could be reduced or come later in the year, and intense bursts of summer rainfall — heavy showers in a short space of time — should also be factored in as a possibility.

This means “fuller water tanks and dams, and the vegetation gets a dousing” in the normally dry season.

On the downside, “it’s not good for deciduous fruit and can encourage diseases”.

He says: “For example, the more cloud, the less chance of fruit ripening, and this is an important time of the year for ripe fruit.”

Inland provinces are in their third consecutive year of La Niña, which often brings above-average rainfall to the summer rainfall region.

In some farmlands, this can bring too much rain and threaten crops, especially at harvest time.

Johnston says the summer rains came late this year in Gauteng, and “it’s been much more intense, so we might find that the same amount of rainfall [or more] occurs but over a much shorter period amid intense thunderstorms”.

However, it is not easy to predict the weather accurately beyond three to 10 days, especially at the scale of individual thunderstorms and hailstorms​.

Accu Weather predicts a hot (26ºC maximum temp), partly cloudy Christmas for Johannesburg, with 50% chance of rain. Cape Town can expect a slightly cooler (23ºC maximum temp), partly cloudy day with no rain forecast. While Durban can expect a cloudy day with temperatures reaching 27ºC and a high chance of showers and thunderstorms.