23 November 2023
The pattern of light rainfall over western grain-producing regions is expected to continue until mid-December.
Light rainfall of about 10 mm per shower that has occurred over the western parts of South Africa’s summer grain areas is expected to continue until mid-December.
“Contributing to the unfavourable rainfall conditions can be the very high temperatures of above 35°C currently occurring in places such as Bothaville, Schweizer-Reneke, Lichtenburg, Klerksdorp and Koppies, persisting at least into the first week of December,” says Johan van den Berg, an independent agricultural meteorologist.
“Temperatures above 30°C can also occur in traditionally cooler regions of the Free State and adjacent parts of Mpumalanga, such as Bethlehem, Vrede and Standerton. In KwaZulu-Natal, very high temperatures can occur in places such as Bergville and Newcastle.”
Underlying this is a low-pressure system over Angola, the Democratic Republic of the Congo, Tanzania and Uganda, as well as the adjacent Indian Ocean, causing fairly heavy rain in those areas. It is also responsible for a high-pressure system with unfavourable rainfall conditions and high temperatures over Southern Africa as part of the Atlantic high-pressure system. The Atlantic high is quite “blocked” over the western parts of the country and is much more static, causing descending air and very dry conditions to persist.
Tropical moisture in December
Van den Berg says medium-term predictions indicate that tropical moisture over Namibia’s northern and northeastern areas may start moving south from early December.
“This is favourable for rain over the northern half of Namibia, but it could also be a precursor for more rain southward and southeastward over South Africa, especially in the second and third weeks of December.”
With this, slightly cooler conditions may occur in the first to middle part of December. “It seems that the first possibly favourable rainfall time slot for summer grain plantings could occur in the second week of December, but general rain is not expected, only a few scattered showers.”
Strategies
Van den Berg says summer grain producers, especially in the western production areas, can consider the following strategies:
- Do not plant in dry soil in anticipation of rain.
- Rain showers are expected to occur in stripes and patches, and it would be advisable to plant the fields with the highest potential first, as soon as sufficient groundwater is available.
- Cash crops with expensive input costs have a very high risk this year on poorer soils. Try to leave these fields fallow or plant forage crops when rain occurs.
- Do not consider late plantings of crops with a longer growing season, such as groundnuts. This also applies to soybeans, which are sensitive to day length. Early frost can damage late plantings.
Consequences of the heat
Van den Berg says the following could be consequences of the warm conditions:
- For irrigation farmers, there can be high water losses that need to be replenished. Evaporation or transpiration losses can progress 6-8 mm or even more per day with hot and windy conditions. Considering that quite a lot of overhead-administered water also evaporates before it reaches the ground, drought conditions can easily arise.
- Summer grain plantings are delayed as the topsoil dries out quickly.
- This reduces the effectiveness of rainwater where it does rain.
- Pastures deteriorate quickly, especially where rain has fallen on burnt fields and field recovery now needs to take place.
Rain for winter rainfall area
Cold fronts have again started moving slightly further north. This caused light rain over the Western Cape and West Coast on November 20 and 21.
Another system may cause further light rain in the last few days of November and the first 10 days of December. Although light rainfall of less than 10 mm and most likely less than 5 mm will occur, the humid and cloudy conditions may be unfavourable for fruit production, with an increased chance of diseases and pests.
