Just when South Africans thought winter’s grip would never be broken, maximum temperatures rose from single digits to above 30 °C within days. Predictions in the first week of October indicated that more snow was possible during the month.
Johan van den Berg, independent agricultural meteorologist, says that although a temperature drop occurred from 7-9 October over southern and eastern parts, it was not as sharp as initially expected.
Central, western and northern parts, including Bloemfontein, Kimberley, Upington, Kakamas, Kuruman, Vryburg, Lephalale, Brits, Mussina and Groblersdal, can experience temperatures of 35 °C or higher until 16 October. Temperatures may drop over southern parts.
“Above-average temperatures can occur over almost the entire rest of South Africa until mid-October. Heatwave conditions are possible especially over the western and northern interior,” says Van den Berg.
According to the South African Weather Service, the definition of a heatwave is three days or longer with temperatures higher than 5 °C above the average maximum for an area.
The average maximum temperature for October for Upington is 29,2 °C. Maximum temperatures higher than 34,2 °C can thus be considered a heatwave if they persist for three days or longer. Current predictions for Upington indicate that temperatures above 34,2 °C will occur continuously until 19 October.
In the next two weeks, heatwave conditions may occur over parts of the western, central and northern interior.
Detrimental to crops
A large fluctuation in temperature has occurred over the past few weeks. On 29 and 30 September, the maximum temperature in Upington was below 20 °C. The expected maximum temperatures for the second week of October are as high as 40 °C, which will be a difference of more than 20 °C.
“The large variation (in temperatures) within a few days is extremely detrimental to crops, because on 30 September it was cold and the signal for plants is not to grow, and from 9 October the signal has been to grow as quickly as possible. This often has a negative impact on the yields and quality of, for example, grapes, but also other crops,” says Van den Berg.
“A crop like winter wheat, which is currently in an advanced reproductive stage, often suffers heat damage, but also drought damage, even under irrigation conditions, because the atmospheric demand is very high. In 2019, similar conditions occurred and there was water loss of more than 7 mm per day during the warm parts of October.”
From 15-17 October, slightly cooler conditions may occur over the eastern parts of the interior, but it will remain very warm over the Northern Cape and Limpopo for the rest of the month.
In 2019, very warm conditions occurred in the second, third and fourth weeks of October, but a sharp temperature drop on 29 and 30 October resulted in catastrophic frost damage.
“Although short-term predictions show that the chance of frost is very small, there is still a frost risk over the central to southern parts. A contributing factor is the very dry air causing desert conditions, with very warm days and cold nights,” says Van den Berg.
