How cold was the winter of 2020 and  what can be expected for the next summer season?


How cold was the winter of 2020 and what can be expected for the next summer season?

Published: 22 July 2020

The winter of 2020 will probably be remembered for the Covit-19 lockdown and secondly for very cold conditions. With global warming in mind was it nearly impossible to think of such a severe winter. Minimum temperatures reached multiple times -5°C or lower and were very close to or even lower than -10°C for places like Standerton, Koppies, Bothaville, Viljoenskroon, Bethlehem, Bloemfontein, Barkley-East and many other places for example Prieska in the Northern Cape and Leeudoringstad in the Northwest Province.  What was further of importance was that the severe cold conditions occurred multiple times since the last week of May 2020. Although the first frost occurred about two to three weeks later than average, was the onset of cold conditions abrupt and continued through June and July. Although a trend developed over the last few years of lesser days with frost, is the 2020 situation 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 of 2001 and 2002 measured only 31 days with frost and was the lowest number of days since 2001 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 and is the second highest number of days since 2001 with only 2007 with more days (54). (The average number of frost days until the end of July since 2001 is 41 days). This demonstrates that the 2020 winter received about 20% more than average days with frost.

Most of the Summer Rainfall Area was in the grip of severe drought conditions since about 2012. Average to above average rainfall occurred in the second part of the summer of 2020 over the central parts. The big question now is if this was the start towards more favourable rainfall conditions for next seasons?

The two most important factors that determines the rainfall over Southern Africa are the ENSO-phenomenon (El Nino 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 Nino-events that drifted between neutral and El Nino type of conditions. Changes in both ENSO and the Indian Ocean started to occur since the beginning of 2020. More La Nina type of development started to occur, 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 Nina conditions as well as a negative phase of the IOD.

The implications of a La Nina 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, 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 start to receive less rain and dry or drought conditions to set in from about February over Mpumalanga, KZN and eastern parts of Limpopo. It is very 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 a second year in a row with record maize yields that may impact on the commodity price of maize but will be positive in terms of food security. In terms of grazing conditions over the central to western parts of the country will the rain likely result in recovery of veld production following the drought conditions of the past nearly eight years. This may lead to higher prices of live-stock due to the building of animal herds.

Summary: In the current poor state of the South African economy can the agricultural sector provide some relief if the favourable climate forecasts are going to materialize.