Rain is possible until the middle of May for the Summer Rainfall Area.
La Nina conditions continue.
Cooler conditions with light rain for the Western Cape in April and first part of May.
Current conditions
Temperatures are starting to drop and although it was not cold enough to cause frost, were minimum temperatures below 10°C recorded from 24 and 28 March in some areas of the Summer Rainfall Area. For example: Koppies and Bloemfontein 6°C, Barkly East 6.3°C, Viljoenskroon 7.1°C, Ficksburg 7.2°C, Bethlehem 7.5°C, Bloemhof 8.7°C and Ottosdal 9.6°C. Minimum temperatures below 10°C are not high enough to sustain growth and development and can slow down growth. It is especially late planted maize and soya beans that are at risk of yield losses.
Rain continues over the central to western parts of the country with regular falls. Lucerne farmers are finding it very difficult to find suitable drier spells without rain or high humidity to make high quality hay. The rain in the Karoo and Kalahari is also stimulating new generations of locusts. Raisin and table grape farmers in the Lower Orange River suffered severe losses due to the rain. On the other hand are grazing conditions very good due to the regular rainfall events and is the drought broken in nearly the whole of South Africa. Rain also occurred for the first time this season in some of the drier areas of the Eastern Cape, but more rain is needed to replenish surface and subsurface water and for recovery of grazing.
Nearly all dams in the Summer Rainfall Area are at very high levels due to the heavy rains. The average level of Free State dams was at 105% in the last week of March. Some dams in the Eastern Cape are still left with low levels. The Kouga dam dropped again to below 15% but the average levels are about 10% higher compared to 56% the same time last year. Western Cape dam levels are at about 61% compared to 56% the same time in 2021 but the rainy season will start within the next two to three months.
The water level in Lake Kariba in Zambia is at about 22% compared to about 43% last year the same time while the Katze dam in Lesotho is at 99.5% and the Mohale dam at 77.4%. The Hardap dam in southern Namibia was at the end of February 2022 at 71.5% of full volume.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
La Nina conditions continue with atmospheric conditions like strong trade winds in the western Pacific; cooler than normal surface and subsurface water in the Nino areas; and Southern Oscillation Index (SOI) that remains in a positive phase. There was an initial weakening of La Nina and associated indicators in January, but it strengthened again in February and March.
Forecasts are very uncertain what to expect for the longer term, especially for the spring and the summer of 2022/23. Current outlooks maintain a near equal probability for La Nina to continue or Neutral conditions, between 40% and 45% probability each. Even with Neutral conditions in the Nino areas can the current La Nina maintain a grip on weather systems for the next months. The probability for an El Nino and possible dry conditions for the summer of 2022/23 is very low (15%).
There will be more certainty from about August about the progress of La Nina or Neutral conditions.
The Southern Oscillation Index (SOI) as indicator of the effect of sea surface temperature interaction with overlying weather systems in the Nino areas, maintains a strong La Nina trend from about July 2021. On a scale from -30 (Strong El Nino) to +30 (strong La Nina) is the current 30-day average SOI +13.03 from a low in January of about +1.5. The current value is the same as during the peak in January 2022 when it was 12.99, indicating the persistence of La Nina values.
2.2 Indian Ocean`
The Indian Ocean Dipole Index (IOD) remains in a neutral state and forecasts are showing that it will remain neutral until at least June when it will move more towards the negative IOD phase in late winter and spring. (A negative IOD is positive for summer rainfall, indicating cooler surface water towards the western Indian Ocean (African coast) and warmer water towards Australia, as was the case in 2021).
3. Rainfall and Climate
3.1 Summer Rainfall Area
Rainfall
The current La Nina continuation is positive for short term rainfall outlooks. If the La Nina remains in place or even if Neutral conditions are to occur through winter and next summer, can the expected impact of the Indian Ocean that is in a negative phase of the IOD, also contributes towards average to above average rainfall conditions for the summer.
Rain is still possible until at least May over most of South Africa.
A dry spell is expected from about June to November that is in line with La Nina that is associated with below average rainfall, especially over the central to western parts.
Average to above average rainfall is again expected from about November 2022 over the eastern production areas and shifting towards the central and western parts in the second part of summer.
Temperature
Temperatures will become cooler in April and drop more sharply in May. Minimum temperatures will be about 10°C in the central to southern parts of the country and Highveld from the start of April but higher for the more northern parts.
The probability for severe frost before the end of April is low but frost is expected in the first week of May. Very cold conditions are possible from the second part of June to second part of August and late frost is again possible in September and even October.
3.2 Winter Rainfall Area
With cold fronts starting to reach over the western and southwestern parts of the country and tropical moisture still present, is there regular light falls of rain possible in the Winter Rainfall Area in April and May. This will also result in cloudy to partly cloudy conditions.
The start to the real winter rainfall season resulting from strong frontal systems that will originate in the southern Atlantic, is likely to be late, only from May or even later. Similar years in history like 1976 and 1989 experienced very stormy conditions and heavy snow falls.
Temperature
Temperatures will be much cooler from now on and it seems that the extremely hot conditions are unlikely to return again before winter.
3.3 Namibia
Rain is still possible until about the second part of May. Very dry conditions are likely to occur until about November/December 2022. With the La Nina still present and Indian Ocean conditions favourable for the next months is it a positive signal for rainfall in mid- to late summer.
4. Summary and conclusion
La Nina conditions continues.
Rain is again expected until about the second part of May for the Summer Rainfall Area but dry conditions from June to November.
Light falls of rain are possible for April and first part of May for the Winter Rainfall Area. The start of the real winter rainfall season is expected from about the end of May. It may be associated with stormy conditions and heavy snow over the higher lying areas.
Independent Agricultural Meteorologist (M.Sc Agric, Agricultural Meteorology, UFS) Johan van den Berg -Climate and agricultural conditions No 61 – March 2022
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