By: Johan van den Berg, Independent Agricultural Meteorologist (M.Sc Agric, Agricultural Meteorology, UFS)
- Favourable winter rainfall conditions are expected for Winter Rainfall Area.
- Cold conditions set in again for the central and southern interior from about 20 June.
- Both Indian Ocean Nino areas relative favourable for summer rainfall. Likely to have an earlier start compared to previous seasons in the central to eastern Summer Rainfall Region.
Very cold conditions started to occur in the last part of May. Minimum temperatures far below freezing point were measured in the first week of June in districts like Devon -8.4°C, Warden -6.9°C, Standerton -6.5°C, Bothaville – 4.8°C and Prieska -4.1°C. Daytime temperatures were also below average. Out of season rainfall occurred in the last part of May and the first week of June in parts of the Free State, KZN, Mpumalanga and Northwest Province with Bothaville measuring more than 20mm, Stella 40mm, Standerton 48mm, Greytown 34mm, Coligny 26mm and Frankfort 21mm.
The harvesting of summer crops is earlier compared to other seasons and can be attributed to early to timely plantings, favourable rainfall conditions in February and drier and hotter conditions in March and April. It also resulting in high quality grains.
Production conditions for winter crops in the Western Cape are very favourable. Sufficient rain occurred over most of the Swartland and heavy falls over the Rûens and rest of the Southern Cape in May, resulting in favourable planting conditions and well within the acceptable planting window. Relative cold and cloudy conditions are also favourable to conserve soil water but also to improve the accumulation of cold units needed for good yields. Production conditions are very favourable for this time of the year compared to previous years.
Grazing conditions are also favourable for most of the country for this time of the year with the exception of the still drought-stricken areas of the southwestern parts of the Northern Cape, adjacent parts of the Western Cape and central to south eastern parts of the Eastern Cape. There was already serious fire damage in the western Free State with above average loads of combustible material with dry and windy weather conditions. The fire risk will increase with increasing cold front activity, resulting in windy conditions.
State of storage dams are in general favourable with the average level in Free State on about 96.8% compared to 83.3% last year the same time. Dams in the Eastern Cape remain at low levels with the Kouga dam at 4.2%, Impofu dam and 15.1% and Bridle Drift dam at 25.9%.
The Clanwilliam dam in the Western Cape started to improve and is currently at about 20% compared to a lower turning point of less than 15% an few weeks earlier. Storage dams in the Western Cape is on average at 54% with the most important storage facility the Theewaterskloof dam at over 80%. This is significant with most of the rainy seasons still ahead and it is expected that most of storage dam levels will improve in the two to three next months.
The water level in Lake Kariba in Zambia is at 53% compared to about 40% last year the same time while the Katze dam in Lesotho is at about 75% and the Mohale dam 36%. The Hardap dam in southern Namibia was at the end of May 2021 at 65.7% of full volume.
ENSO and Indian Ocean
ENSO (El Nino Southern Oscillation)
All Nino areas were at normal or long-term average temperature levels in the third week of June 2021. It is expected that it will remain neutral until at least September to November 2021. Current forecasts indicate the development of a weak La Nina from about September/October but it is still uncertain whether it will remain at neutral levels or can develop to reach the La Nina threshold. There is a 90% certainty that it will not develop towards El Nino levels.
The Southern Oscillation Index as indicator of the effect of surface conditions in the Nino areas and overlying atmosphere is also at neutral levels.
Indian and Atlantic Ocean
A thin stretch of cooler than normal waters in the western Indian Ocean (adjacent to the Africa coastline) from southeast of Cape Town up to the Red Sea, was present towards the middle of June 2021. Warmer than normal waters are however present in a line north/south to the east of Madagascar towards Australia that represents about 70% of the total surface area of the Indian Ocean.
This type of situation is consistent with a negative phase of the Indian Ocean Dipole (IOD) index. Forecasts also favour a strengthening of the negative IOD in months to come. A strong IOD is positive for increased rainfall probabilities for Southern Africa for the spring and summer.
Atlantic Ocean temperatures towards the west coast of Africa, stretching from Cape Town in the South to the northern parts of Angola, are warmer than normal for this time of the year. Cooling started to take place since the second part of May 2021 and it is expected that it will be at normal levels towards the end of July.
It is most likely that conditions in the Indian Ocean will be the main driving force of climate and weather patterns over Southern Africa in the next months and even the summer of 2021/22 with ENSO at neutral to weak La Nina levels.
Rainfall and Climate
Summer Rainfall Area
Short term outlooks for the rest of June and July are negative in terms of significant rainfall but that is expected being a summer rainfall area. If the current neutral conditions of ENSO change to La Nina levels towards spring, it can enhance the probability for spring and early summer rain. With current favourite Indian Ocean conditions (negative IOD) and forecasts to remain in the negative phase of the IOD, it can enhance the probability for early rain this season.
Rainfall outlooks for the summer of 2021/22 are positive for the central to eastern parts of Southern Africa from about October but less favourable for the western parts. If La Nina development takes place in early summer, it can further enhance the probabilities for rain, even for the more western parts.
In general are rainfall outlooks positive for most of the Summer Grain Area from about the middle of October, starting from the eastern production areas and extending to the western areas in November. Drier conditions are possible towards February 2022 for the eastern production areas and will it be advisable to plant as early as temperatures dictate in these areas.
Following a spell of moderate temperatures from about 8 June until 16 June, very cold conditions can again set in from about 20 June over the central to southern interior, especially from 24 to 27 June when minimum temperatures are expected to be well below freezing point. Extreme cold conditions are again possible in the second and third week of July.
Frost is expected to last into spring and late frost is again possible, taking the late start as well as cooler western Indian Ocean surface temperatures into account.
Most winter months that followed La Nina events (like 2021) resulted in heavy snow falls. It is possible that snow can occur in the mid to late winter months.
Winter Rainfall Area
There was a drier spell in the first two weeks of June 2021 for most of the Winter Rainfall Area following good falls in May. Short term outlooks are positive for significant rainfall of more than 30mm in the last 10 days of June for most of the Swartland, Winelands, Cape Town Metropole and Rûens. Less rain is expected towards the South Coast and Garden Route.
Not much rain is expected for the central to northern parts of the West Coast as well as adjacent interior.
Longer term outlooks are positive for most of the winter but uncertainty about the important second part of August and September.
Little or no rainfall is expected for the winter and spring. Outlooks are positive for summer rainfall starting from about November 2021.
Temperatures will be very cold from the end of June and frost can be expected for most of July up to the northern parts.
Summary and conclusion
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