Certain parts of South Africa are more prone to extreme rainfall due to climate change, a study by experts at the University of Pretoria (UP) has found.

Researchers found that rainfall in several areas ‘have increased or become more extreme over the past 50 years or so’.

The team, led by Charlotte McBride of the South African Weather Service and a PhD candidate in UP’s geography, geoinformatics and meteorology department, found that an increase in weather and climate extremes (such as heatwaves, heavy rainfall, floods, droughts and tropical cyclones) are a result of human-induced climate change.

“South Africa is currently focused on flooding, as this is what is happening at the moment,” she says. “However, during 2018 and the Day Zero debate – when Cape Town was set to run out of water – the public’s attention was focused on drought. South Africa has a variable climate, with droughts and floods a common feature of this variability,” McBride explains.

She adds that the water content of the atmosphere changes as surface temperatures increase due to climate change.

“These increases in the water-holding capacity of the atmosphere equate to about 7% per degree of warming. With more moisture available, the nature of rainfall events is likely to become more intense, with increased rainfall rates. However, changes in extreme rainfall patterns are thought to be highly regionalised,” McBride explains.

Country’s rainfall

It is said that South Africa’s annual rainfall distribution is ‘diverse, and increases from below 200mm in the west to above 1 200mm a year in the east’.

The researchers examined 70 manual rainfall stations’ daily time series between 1921 and 2020. Sub-periods of 1921–1970 and 1971–2020 were created and ‘it became evident that most rainfall stations showed an increase in their 1–50- and 1–100-year return period values’.

“The two periods had more or less the same number of rain days (more than 1mm), but the rainfall amounts on any given rain day for certain parts of the country increased or became more extreme in the latter period.

“We then mapped the change between the two periods as a ratio for each station. This gave us an idea of where areas are experiencing higher or lower rainfall values for the specific return periods,” McBride explains.

The research states that increases of more than 100mm in the later period were noted at some stations over the eastern parts of the country.

For example, the Letaba district rainfall station in Limpopo experienced an increase of more than 35%. Another example is Hlobane in KZN, where the 1–50- and 1–100-year values have essentially doubled. This means that these areas and others highlighted in the research, such as the western interior and southern parts of the country, are likely to experience more extreme rainfall, which is probably a feature
of climate change over those areas.

Impact on the future

McBride says it is likely that the country will become warmer and have increased occurrences of droughts. “However, this does not mean that the risk of severe storms – including tropical cyclones and intense thunderstorms – will not be expected to occur. With the atmosphere heating, it can hold more water vapour. More water vapour means more rainfall. So, we can expect the intensity of rainfall to increase.”

Associate professor in Meteorology at UP Liesl Dyson says locally and internationally, a lot of work is done on climate change by using Numerical Weather Prediction data.

“While these products are of great value and provide insight into what could happen in a future climate, they remain proxies of reality. The value of the presented research is that it uses real, observed data of rainfall over South Africa for an extended period,” she adds.

“These results are based on what we know has happened over the past century, and show that in general, rainfall extremes are becoming more probable and therefore increasing in South Africa,” Dyson explains.

She adds that researchers who make use of the data set could use these results to verify that the models they employ capture the current situation accurately, ‘thereby placing a higher value on the reliability of projections in the future’.