The winter of 2020 will probably be remembered for the Covid-19 lockdown and secondly for very cold conditions. With global warming in mind, it was nearly impossible to think of such a severe winter. Minimum temperatures reached -5 °C or lower multiple times and came very close to or even lower than -10 °C for places like Standerton, Koppies, Bothaville, Viljoenskroon, Bethlehem, Bloemfontein, Barkley-East as well as Prieska in the Northern Cape and Leeudoringstad in the Northwest Province.
Also notable was the severe cold conditions that occurred multiple times since the last week of May 2020. Although the first frost occurred about two to three weeks later than average, the onset of cold conditions was abrupt and continued through June and July. A trend has developed over the last few years of fewer days with frost, but the 2020 situation was probably more reminiscent of the long-term average or “normal”. The average number of frost days for a place like Bothaville (Nampo) since 2001 is about 50 days. The years 2001 and 2002 measured only 31 days with frost, while the winters of 2007 and 2011 recorded the highest number of frost days with 66 days each. The total number of frost days for Bothaville for 2020 until the end of July were 51 days which is the second highest number since 2001. Only 2007 had more frost days (54). (The average number of frost days until the end of July since 2001 is 41 days). This demonstrates that the 2020 winter experienced about 20% above average frost days.
Most of the Summer Rainfall Area has been in the grip of severe drought conditions since around 2012. Average to above average rainfall occurred in the second part of the summer of 2020 over the central parts.
The big question is whether this was the start of more favourable rainfall conditions for subsequent seasons.
The two most important factors that determines the rainfall over Southern Africa are the ENSO-phenomenon (El Niño Southern Oscillation) and the status of sea surface temperatures of the Indian Ocean, especially the western Indian Ocean. Both the 2018/19 and 2019/20 seasons resulted in weak El Niño-events that drifted between neutral and El Niño type of conditions.
Changes in both ENSO and the Indian Ocean began in early 2020. A La Niña type of development emerged especially since the beginning of May 2020. The Indian Ocean Dipole (IOD) index is also now well within the neutral range. Most forecasts favour a further development towards La Niña conditions as well as a negative phase of the IOD.
The implications of a La Niña event that coincides with a negative IOD usually result in positive prospects for summer rainfall. Analogue or similar years in term of ENSO and the IOD in history were 1974/75 and 1988/89, and both resulted in above average rainfall and even flooding. A characteristic of similar years was the normal to late start of the rainy season. There is also a unique spatial pattern with average to above average rainfall starting from about October to reach a peak in December over the eastern parts of the country. The band of rainfall then starts to shift towards the west with above average rainfall over the central to western parts from January to March. As the rainfall pattern shifts towards the west, the eastern and north eastern parts receive less rain and dry or drought conditions begin to set in from about February over Mpumalanga, KZN and eastern parts of Limpopo. It’s quite likely that average to above average rainfall will occur over the current drought-stricken areas of the Northern Cape and adjacent parts of Namibia and Botswana.
Implications for agriculture
Favourable prospects for summer crop production are very likely for the 2020/21 summer season, especially over the central to western parts. It may result in the second year in a row with record maize yields which may impact the commodity price of maize, but will be positive in terms of food security. For grazing conditions over the central to western parts of the country, the rain will likely result in recovery of veld production following the drought conditions of the past nearly eight years. This may lead to higher prices of livestock due to the building of animal herds.
In the current poor state of the South African economy, the agricultural sector may provide some relief if the favourable climate forecasts do materialise.