Cold conditions persist and will continue until at least the middle of September. Rain in the Winter Rainfall Area also likely to continue until at least the end of September or even later.
A pending La Nina is in its initial stages of development combined with a favourable Indian Ocean set up are very positive for summer rainfall.
Current conditions
Extreme cold conditions persisted for most of July and August especially over the central to southern parts of the country. Snowfalls occurred regularly over the higher lying areas of the Western-, Northern- and Eastern Cape and Lesotho.
Regular rainfall events resulted in very favourable productions conditions for winter grains in the Winter Rainfall Area of the Western Cape. Significant rain also occurred in the Langkloof and replenished water levels in smaller storage dams in this area where water shortages are a real threat to sustainability of fruit production. Between 20mm and 50mm occurred over the central parts of the country, stretching roughly from Kuruman in the north to Bloemfontein and Wepener in the south east and Prieska in the west during the weekend of 14 and 15 August. Light falls also occurred over the northern parts of the Eastern Cape, Eastern Free State and southern parts of KZN. Very little rain occurred in the very dry Baviaanskloof area and adjacent districts like Jansenville where the drought still intensifies. The southern and southwestern parts of the Northern Cape, especially Boesmanland and southwestern Karoo are still in the grip of very intense drought spell.
Grazing conditions are in general favourable for most of the country for this time of the year, but quality now rapidly starts to deteriorate. With the fire season now in full swing, are there already large areas where wildfires already destroyed natural veld. Although soil water conditions are still relatively favourable following the rain in the pre-winter period as well as the rain over the central grass lands in mid-August, are temperatures still too low for any growth and development or recovery of vegetation.
State of storage dams are in general still favourable with the exception of some dams in the Eastern Cape that remains at critical low levels or near empty. Western Cape dam levels are on average close to 80% with most of the large and important dams that are close to or over 100% of capacity with further rainfall and replenishment of dams expected in September.
The water level in Lake Kariba in Zambia is at about 45% compared to about 36.5% last year the same time while the Katze dam in Lesotho is at about 66.4% and the Mohale dam 30.9%. The Hardap dam in southern Namibia was at the end of August 2021 at 60.5% of full volume.
ENSO and Indian Ocean
ENSO (El Nino Southern Oscillation)
ENSO is currently borderline between neutral and weak La Nina but is starting to move more towards La Nina. The important Nino3.4-area reached a value of -0.9°C cooler than normal at the end of August that represents already a weak La Nina if cooling is going to persist. To be classified as a La Nina, temperature deviations of -0.5°C or cooler must be present for at least three to 5 consecutive months. Of importance of the current situation is the huge area with cooler than normal surface temperatures that is present, although not yet very intense. The pool of cooler water in the Pacific stretches from the northern parts of the USA west coast, south to about the middle of South America and west just to the northeast of Australia. The extent of the area can replace the effect of a lack of cooler waters of the Nino-areas to present La Nina like trends. One of the already known effects is the drought in the USA northwest.
Subsurface temperatures in the Nino areas showed a rapid cooling to a depth of about 250m since the beginning of August, assuring the development of the La Nina.
The Southern Oscillation Index (SOI) as indicator of the effect of surface interaction with overlying weather systems in the Nino areas, are already in a La Nina trend since about the middle of June 2021.
Indian Ocean
Further cooling of surface temperatures took place in the second part of August 2021 over most of the western and southwestern Indian Ocean. Almost the entire western Indian Ocean from the Horn of Africa down to Cape Town is now cooler than normal. This is a unique set up that does not happen very often and is very positive for summer rainfall. Warmer waters are present to the east.
This type of situation is consistent with a negative phase of the Indian Ocean Dipole (IOD) index and is expected to last until at least midsummer.
Rainfall and Climate
Summer Rainfall Area
Rainfall
Relative strong low-pressure systems already started to develop with rain over parts of the Summer Rainfall Area. This can be the first indications of a favourable summer rainfall season. It is anticipated that the effect of the Indian Ocean in its current state can be responsible for an earlier onset of more general summer rainfall. A La Nina phenomenon is usually associated with a late start of the rainy season, but the earlier rain that already occurred, may well be an illustration of the effect of the Indian Ocean on rainfall.
The combined effect of La Nina and the negative Indian Ocean Dipole (IOD) can result in very favourable rainfall conditions for most of the summer.
It is possible that less favourable conditions may occur in the second part of the summer season over the eastern production areas that includes KZN, Mpumalanga and eastern Free State. It is also still uncertain about the rainfall conditions for the drought stricken Boesmanland and Karoo in the south western Northern Cape. A weak La Nina usually is responsible for average to above average rain over the central to eastern Summer Rainfall Area.
Rainfall conditions are positive for the Eastern Cape and average to above average rainfall is expected in the next months. Heavy falls and flooding are not excluded for these area.
Temperature
Cold conditions with snow persisted throughout August in the southern parts of the Summer Rainfall Area. It is likely that cold or below average temperatures may continue for most of September with a rapid change to hot conditions in October.
Winter Rainfall Area
Most of the Winter Rainfall Area experienced a very favourable rainfall season, not only in the amount of rainfall but also the distribution over time. Outlooks are still positive for further rain in September with expected rainfall events from about 5 to 8 September, 11 to 13 September and 16 to 18 September. This is very positive for winter grain production with very good yields expected.
Namibia
Little or no rainfall is expected until at least the middle of October. Outlooks are very positive for summer rainfall, starting from about November 2021.
Minimum temperatures will still be below average and mostly below 10°C for at least the first three weeks of September for the central to southern parts of the country. Very warm to hot over the northern parts from about the second week of September.
Summary and conclusion
It is relatively sure that a weak to moderate La Nina event will occur for the summer of 2021/22, currently still in a developing phase and uncertain about the final intensity.
Favourable Indian Ocean temperatures in combination with a La Nina are positive for average to above average rainfall for the Summer Rainfall Area.
Rainfall conditions are positive for most of the Winter Rainfall Region until at least the second part of September with regular frontal activity with rain and cold conditions.
Cold conditions and frost over the central to southern parts of the country can be expected until at least the second part of September.
Disclaimer:
The author or Santam or any other parties mentioned in this document do not warrant the accuracy, completeness or reliability of any information in this document. Any actions or decisions based on the information in this document is strictly at your own risk and we will not be liable for any losses or damages in connection with the use of information stated in this document.
Johan van den Berg
Independent Agricultural Meteorologist
(M.Sc Agric, Agricultural Meteorology, UFS)
