Climate and Agricultural Conditions- South Africa- March 2021 .
Sponsored by Santam Agriculture -Johan van den Berg -Independent Agricultural Meteorologist (M.Sc Agric, Agricultural meteorology, UFS)
Important Issues
Less rain occurred since the second part of February in the central to western Summer Rainfall Area but conditions for rain will improve again towards the end of March and beginning of April.
La Nina started to weaken but will remain at moderate La Nina levels and will last until April/May.
1. Current conditions
Drier conditions occurred since the second week of February over the central tot western parts of the country, but widespread showers still occurred for most of February over the Northwest Province, Gauteng, Limpopo, KZN and parts of the Free State and northern Eastern Cape. Localised heavy falls of more than 50mm were recorded in areas like Mussina, Vryburg, Klerksdorp, Secunda, Madikwe, Machadorp, Tzaneen, Richards Bay and Wepener.
Tropical low-pressure storms in and around the Mozambique Channel were responsible for less rain over the central to western interior. Tropical cyclones (rising air) in the area of Madagascar are responsible for the development and presence of high pressure systems (falling air) over the western parts of South Africa and Namibia, dominating the upper air conditions with unfavourable conditions for rain.
Drier conditions were welcomed over most of the Summer Grain Production areas following the heavy falls of rain at the end of January and first week of February. The sunny and hot conditions resulted in recovery of crops or stabilizing the deterioration of crop conditions and dried out water-logged conditions in many areas. Permanent damage occurred to the maize crop in the north west Free State and adjacent parts of Northwest Province in districts like Wesselsbron, Bothaville, Bultfontein, and Wolmaranstad. Record yields are expected in areas where water logged conditions did not occur in districts like Koppies, Kroonstad, Lichtenburg, Schweizer Reneke and Delareyville that usually are suffering from lack of rainfall.
Drought conditions still are responsible for disastrous conditions for farming in most of the south western parts of the Northern Cape. Some rain in the Kalahari brought relieve but the lack of follow up rain, especially towards the western parts now again threaten grazing conditions with the winter at hand. Very good falls of rain over the western parts of the Northwest Province in districts like Vryburg and adjacent Kuruman and Vanzylsrus in the Northern Cape, resulted in very good recovery of grazing conditions after the extreme drought conditions.
No or very little relief took place in the central to eastern parts of the Eastern Cape, south and south east of Graaff Reinet up to the coast, including Port Elizabeth.
Levels of nearly all larger storage dams in the central tot eastern parts of the country are at 100% or close to 100%. The only areas/dams still at low levels are in the Eastern Cape with the main dams providing water to the Nelson Mandela Metro, the Kouga dam with less than 7% and Bridle drift dam with less than 35%, at very low levels.
The water level in Lake Kariba in Zambia increased to 37% compared to the 11% last year the same time while the Katze dam in Lesotho increased to 78% compared to 33.6% last year the same time. The Hardap dam in southern Namibia was at the end of January 2021 at 72.6% of full volume.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
Sea-surface temperatures remain at La Nina levels with all four main Nino-areas between 0.9°C and 1.2°C cooler than normal. There was a brief period of warming in February to levels between 0.5°C and 0.9°C cooler than normal but there was some cooling again in the last part of February.
ENSO typically returns to neutral values in winter and again develop towards either El Nino, La Nina or remain neutral from about August.
Longer term forecasts favour a return to La Nina or neutral levels from about August/September with a very low probability for the development of El Nino.
2.2 Indian Ocean
Most of the Indian Ocean still indicates cooler than normal sea surface temperatures although there appeared a pool of warmer water from Mozambique across the Channel and south east wards into the Indian Ocean. This pool of warmer surface water is responsible for tropical depressions and storms over this part of the Ocean. There was however a warming trend since the beginning of February over most of the Indian Ocean although still below the average temperatures for this time of the year. A pool of cooler surface water is now starting to develop along the east African coastline across the Mozambique channel to the north coast of South Africa.
The Indian Ocean Dipole (IOD) index remains in a neutral phase and forecasts indicates that it will remain neutral or negative (cooler than normal in the western Indian Ocean) for the next at least six months.
3. Rainfall and Climate
3.1 Summer Rainfall Area
Tropical depression/cyclone activity temporary inhibit rainfall conditions since the middle of February over the central to western parts. With changes in the Indian Ocean expected, is it likely that rainfall conditions will again improve in April and May. Less tropical storm activity will assist in tropical moisture once again to shift back over Botswana and Namibia before the end of the rainy season and improving conditions for rainfall over South Africa again. Average to above average rainfall is still expected over the country, especially towards the central to western parts of the country.
The currently still very dry southwestern parts of the Northern Cape and central to south eastern parts of the Eastern Cape can still expect rain before the end of the rainy season. The months with the highest long term average rainfall for these areas are between February and April, leaving at least two months of the rainy season to come.
With the possible return to La Nina conditions and relative favourable Indian Ocean surface conditions from about August 2021, is it very possible for further favourable rainfall conditions for the 2021/22 summer season.
Temperature
Relative warm to hot conditions will remain prevalent for most of March. Minimum temperatures are also not expected to drop below 10°C before the middle of April with first frost date projections towards the end of April for the central to southern parts and towards middle to end of May for the central to northern parts.
3.2 Winter Rainfall Area
Very little or no rain is expected for most of the Western Cape with the exception of the southern eastern parts from about 20 March where light falls are possible. The current La Nina phase that remains in place is a late start to the normal winter rainfall season very possible, especially for the southwestern Cape and West Coast areas. The Southern Cape and Garden Route with adjacent interior can however expect rain from summer rainfall weather systems in April and May.
3.3 Namibia
Forecasts still favour average to above average rainfall for most of Namibia for April and May due to the impact of the current La Nina event remaining in place. The central to northern parts are more likely to receive rain than the south western parts.
4. Summary and conclusion
Following a drier spell since the middle of February is it possible that rainfall conditions will only start to improve from the second part of March for the Summer Rainfall Area.
The current La Nina event returned to stronger levels after a slight warming spell but it is now down scaling to become neutral in about April/May. It is still strong enough to impact positively on summer rainfall.
A late start to the winter rainfall is possible due to the effect of La Nina that remains in place.
