Important Issues:
La Nina reached maturity but will impact on rainfall conditions until about May 2022 with further average to above average rainfall possible from the second part of February (Summer Rainfall Area).
Current conditions
Extreme wet conditions occurred in December 2021 and first part of January 2022 over large parts of the Summer Rainfall Area. Many areas received rainfall amounts equal to or more than the annual expected rainfall during these two months. What is also of importance is that the rain occurred as very heavy showers of 100mm or more per event that caused flooding and water logged conditions. Flooding occurred randomly in areas like Hoopstad and Bultfontein in the northwest Free State, in the Eastern Cape near East Londen, Northern Cape near Augrabies, several areas in Limpopo and even in the very dry parts of the northern Cape. Flooding also occurred in several parts of KZN.
Most areas in the drought stricken Northern Cape received very good falls of rain but follow up rain is still needed. More rain is still needed before winter for sufficient recovery to take place because the most productive production spell is in the late summer and autumn.
Parts of the Eastern Cape near Cradock as well as in the vicinity of Jansenville and Steytlerville are still in the grip of a drought. Even parts of the Langkloof near Uniondale are still dry with smaller storage dams with very low water levels.
Nearly all dams in the Summer Rainfall Area were at very high levels due to the heavy rains. Only some dams in the Eastern Cape are still suffering low levels although there was a rise in levels. The Kouga dam are still at about 17% although there was an increased in the level from the 5% a few weeks earlier.
The water level in Lake Kariba in Zambia is at about 20.7% compared to about 21% last year the same time while the Katze dam in Lesotho is at 100% and the Mohale dam 64%. The Hardap dam in southern Namibia was in the middle of January 2022 at 50% of full volume but rain from 21 to 23 January resulted in an increase to about 67%.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
Sea surface temperatures in the Nino areas now reached a peak, meaning the current La Nina reached maturity. La Nina conditions will still remain present until at least early winter when it will return to neutral conditions. ENSO is usually in a neutral state from about April to June when changes are taking place before the start of the Southern Hemisphere Summer. Current forecasts for ENSO conditions for the 2022/23 summer season are very inconclusive, ranging from return to La Nina or development of an El Nino. The scenario currently for 2022/23 is an about 50% probability for neutral conditions to continue from late autumn and a 20% to 30% probability each for La Nina and El Nino, respectively. More certainty will only be available from about July 2022 what to expect for the next summer season.
The Southern Oscillation Index (SOI) as indicator of the effect of sea surface temperature interaction with overlying weather systems in the Nino areas now returns to neutral levels for the first time since July 2021. On a scale from -30 (Strong El Nino) to +30 (strong La Nina) is the current 30-day average SOI about +1.6 from a high in December of about +13.
2.2 Indian Ocean`
The Indian Ocean Dipole Index (IOD) remains in a neutral state although there was some warming in die western Indian Ocean to the north of Madagascar. This warming is currently responsible for the development of tropical storms, disrupting rainfall to Southern Africa over the short term.
The first tropical storm (not strong enough to be classified as a tropical cyclone) called “Ana”, developed in the last week of January 2022. Maximum wind speeds of between 70km/h and 80km/h were reached when it made landfall over central Mozambique in the last week of January. Tropical storm “Ana” will rapidly weaken before reaching the northern parts of Zimbabwe.
“Ana” is the first tropical storm in the Indian Ocean this season as indicated by the first letter of the alphabet. There are usually between about 10 and 25 tropical storms or cyclones annually from about December to March in the Indian Ocean.
There are indications that more tropical storms can develop in the first two weeks of February.
3. Rainfall and Climate
3.1 Summer Rainfall Area
Rainfall
Although La Nina reached maturity in die middle part of January 2022, will it still be prominent in terms of rainfall in the pre-winter period. The following are expected for the next months:
A drier spell from about the last week of January until the second part of February, especially over the central to western parts. Rain is however possible in the first week of February over the central to eastern parts when the effect of tropical storm “Ana” weakened.
Conditions will in general again improve from about the second part of February, initially over the eastern parts and gradually expanding to the central and western parts until about the middle of March.
Drier conditions are possible in March over the eastern parts with rainfall conditions shifting to the west and south in March and April with average to above average rainfall possible. It is anticipated that significant rainfall is therefor also still possible over the Northern Cape as well as the still very dry Eastern Cape.
Temperature
Temperatures will be about average to above average until the second part of February when rainy conditions are likely to return, keeping temperatures in general lower.
The probability for early frost is very low and severe frost is not expected before the middle of May.
3.2 Winter Rainfall Area
Very little rain is expected over the South-Western Cape for February but with anticipated summer systems to return over the far western parts of the country in March and even April, is it likely for summer rainfall conditions with thundershowers to occur. The start to the winter rainfall season from frontal systems that will originate from the southern Atlantic is likely to be very late, only from May or even later.
More rain is possible for the rest of summer over the Southern Cape and Garden Route from more typical summer rainfall systems.
Temperature
Hot to very hot conditions are expected for at least the next six weeks, especially over the central to western parts of the Western Cape.
3.3 Namibia
Very little rain occurred over most of Namibia up to the middle of January 2022. Tropical moisture from central and west Africa was more redirected over Botswana towards South Africa, skipping most of Namibia. Heavy falls of rain started to occur in the third week of January over large parts of Namibia, even with localised flooding.
Longer term outlooks for rainfall are still very positive in the pre-winter period. The impact of La Nina is still eminent for average to above average rainfall to occur. Rainfall conditions will start to improve again over the northern parts from the second part of February and extending to the central and southern parts before winter.
4. Summary and conclusion
La Nina reached maturity in the middle of January 2022 but will still impact on rainfall and climate conditions until late autumn.
A drier spell over the Summer Rainfall Area until about the middle of February can be very beneficial for recovery of gains crops.
Rainfall outlooks are still very positive for most of the Summer Rainfall Area from the second part of February.
The south western parts of Winter Rainfall Area can still expect dry and hot conditions until at least the end of February or even later but more rain and cooler conditions are possible over the Southern Cape in the pre-winter period. A very late start of the real winter rainfall season is anticipated.
Johan van den Berg
Independent Agricultural Meteorologist (M.Sc Agric, Agricultural Meteorology, UFS)
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