La Nina sharply bounced back in the first part of August to relative strong levels for this time of the year. It is anticipated that La Nina-levels will be maintained until about December/January before weakening in the second part of summer. The Indian Ocean also rapidly moved into a negative phase of the Indian Ocean Dipole.
The La Nina and Indian Ocean developments are both very positive for summer rain from about September/October over the eastern parts and November/December over the central to western parts
Rainfall conditions for the Winter Rainfall Area improved over the short term. Possible rain in November with strong summer systems.
Extreme cold conditions again from 18 to 21 August and cold conditions also possible in the first week of September.
Late frost events again likely in spring and early summer over the central to southern interior.
1. Current conditions
Very dry conditions with less than 50% of the long-term average rainfall occurred over most parts of the Winter Rainfall Area in the second part of June, whole of July and first two weeks of August, putting winter grains in jeopardy of drought damage. For example: Malmesbury in the Swartland received from 1 May 2022 up to 16 August 2022 only about 130mm compared to the long-term average of about 210mm (62%). Bredasdorp in the Overberg received also about 130mm compared to the long-term average of about 170mm (75%).
From an agronomical perspective is the vegetative stages of winter grains less important in terms of drought sensitivity but the reproductive stages that will start to develop from the second part of August but especially September, can induce severe crop losses. It seems however that rainfall conditions are starting to improve for the rest of August and September (see section about Winter Rainfall forecasts, 3.2).
The summer crop harvesting process is completed with highly variable yields harvested, ranging from record yields in well drained soils to nearly total crop failures where water-logged conditions occurred. In some areas are fields still very wet and water-logged that can pose serious problems to cultivate and plant in the coming summer season.
One of the most serious risks for live-stock farmers are the mouth-and-foot disease outbreak. Springtime is the most important period to sell off breeding stock and if it is not possible and with too many animals on the farm, the cost of feeding animals can seriously impact on cash flow and available food resources. The feeding quality of natural grass veld is also very low due to the above average rainfall in the 2021/2022 summer season, leaching out nutrients in the soil.
The fire season is now in progress with increased windy and hotter conditions. With rain still absent until at least the end of October, can September and October see a very high fire risk.
Storage dams in the Summer Rainfall Area are still at very high levels with Free State dams at 99.6% of full capacity. On 15 August was the Vaal dam still at 100.1%, Bloemhof dam at 106%, Vanderkloof dam at 99.5% and Gariep dam at 97.7%. Western Cape dams are about 15% lower compared to 2021 but still about 65% of full capacity towards the middle of August 2022 (Last year this time about 78% full).
Eastern Cape dams are in general about 18% fuller compared to last year, but critically low levels are still observed in the important Kouga dam (16.7% compared to 4.5% last year) and Impofu dam (10% compared to 16% last year).
The water level in Lake Kariba in Zambia is at about 27% compared to 46% last year the same time while the Katse dam in Lesotho is at 88.5% and the Mohale dam at 100.1%. The Hardap dam in southern Namibia was in the middle of August 2022 at 63.1% of full volume while the largest storage dam, the Neckartal dam, at 97.7%.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
The important Nino3.4 area cooled down in the past weeks from about 0.5°C cooler than normal in July to about 1.1°C cooler than normal (representing a moderate La Nina although it may be temporary). This value of -1.1°C sea surface temperature deviation is very close to the peak that was reached in May 2022 of about -1.2°C. It is very significant compared to August 2021 when it was about 0.2°C cooler than normal, well within the neutral range at that stage. La Nina conditions only started to develop in October of 2021.
This value reached in August 2022 compares very favourable to the August values in the previous strong La Nina events of 1973 (-1.1°C), 1975 (-1.1°C), 1988 (-1.3°C), 1999 (-1.0°C) and 2010 (-1.0°C).
Most forecasts converged towards a weakening of La Nina from about December 2022 to reach neutral values (between +0.5°C and -0.5°C) from about January/February 2023.
2.2 Indian Ocean
The Indian Ocean Dipole Index (IOD) entered a strong negative phase in July 2022 and to last until about December 2022. (A negative IOD is indicating cooler surface water towards the western Indian Ocean (African coast) and warmer water towards Australia). (See the impact on rainfall in the next Section (3.1 Summer Rainfall Area).
The current IOD index is much stronger compared to the same time last year and one of the strongest developments in at least the last five to ten years. This is a very significant development, taken also the La Nina development into account.
3. Rainfall and Climate Outlooks
3.1 Summer Rainfall Area
With strong positive rainfall signals from both La Nina and the negative phase of the IOD, are the following the most probable outcomes in terms of rainfall and temperature:
3.1.1 Limpopo, north Gauteng, northern parts of KZN and Lowveld:
Long term: Below average rainfall until about the end of October but average to above average rainfall from November to February. Probable drier conditions in the second part of summer from February to May. Frost can be expected until the first week of September over the southern parts of Limpopo and adjacent parts of Gauteng.
Short term: Very little or no rain until at least the end of September.
Temperature: Very hot conditions can be expected over the western parts from about the second part of September and most of October.
3.1.2 Southern Gauteng, Highveld of Mpumalanga, and north-eastern Free State:
Long term: Below average rainfall until middle October but average to above average from November to January. Drier spell from about February. Frost possible until about the first part of October.
Short term: Very little or no rain until at least the end of September. Frost conditions possible from 18 to 21 August.
Temperature: Low minimum temperatures (between 5°C and 8°C) until the middle of September but will rapidly warm up from the last part of September.
3.1.3 Northern Cape (north of Orange River), Northwest Province and central/western Free State:
Long term: Below average rainfall until about middle November but average to above average from December to February. Drier spell from about the end of February. The probability for late frost is again high with frost possible until about the middle of October, especially the southern parts.
Short term: Very little or no rain until at least the end of October. Frost expected from 18 to 21 August as well as in the first week of September.
Temperature: Very hot from the last part of September but especially October and first part of November
3.1.4 Eastern Free State, southern parts of KZN and northern parts of the Eastern Cape:
Long term: Rainfall conditions will start to improve towards the second part of September but average to above average from October to January. Low minimum temperatures until about the end of September.
Short term: Light rain with a possibility of snow over the higher lying interior of the Eastern Cape from 19 to 21 August. Extreme dangerous conditions for livestock in the open.
Temperature: Very cold conditions with frost possible from 18 to 21 August as well as in the first week of September.
3.1.5 Southern parts of the Northern Cape and adjacent areas of the Eastern Cape
Long term: Below average rainfall conditions until about October/November. Average to above average rainfall from about December. Very cold conditions still possible until at least the end of September with frost.
Short term: Light rain possible towards the end of August.
Temperature: Very cold conditions to prevail until about the third week of September.
3.1.6 Coastal areas of the Eastern Cape as well as rest of Garden Route
Long term: There is a high probability for rain from about September with the migration of winter to summer rainfall conditions along the east coast. There is even a flood risk, especially the Eastern Cape coastal areas.
Short term: More than 20mm of rain is possible from 18 to 31 August but it will not be sufficient to replenish storage dams.
Temperature: Cool to moderate but hot from about October.
3.1.7 KZN interior and northern coastal areas
Long term: Rain is possible over the coastal areas from about September and can migrate later into the northern interior.
Short term: Light rain is possible in the last week of August, especially the coastal areas.
3.2 Winter Rainfall Area
Long term: Average to below average rainfall September and October but there is an increased probability for rain in November with the La Nina development.
Short term: Short-term outlooks are more positive compared to a few weeks earlier. Between 20 and 50mm is possible before the end of August over some areas, especially the winter grain areas. Timing of rainfall is very significant with winter grains now entering the reproductive stages. Regular smaller amounts of rainfall can be very beneficial to prevent drought damage.
3.3 Namibia
Very little or no rain is expected until at least November but average to above average rainfall from the last part of November to February. Temperatures will be warm to hot over the central to northern parts from the last week of August but cool to cold with frost from 18 to 21 August in the southern parts.
Johan van den Berg
Independent Agricultural Meteorologist
(M.Sc Agric, Agricultural Meteorology, UFS)
