By: Johan van den Berg, Independent Agricultural Meteorologist (M.Sc Agric, Agricultural Meteorology, UFS)
- Cold and wet winter expected over the Western and Eastern Cape.
- Dry winter conditions and high wildfire risk in most of the Summer Rainfall Area.
Below-average rainfall occurred over most of the country in March and April 2021 due to the weakening of the La Nina event since the second part of February 2021. It was anticipated that the La Nina that developed in the spring of 2020 would last until April 2021 but it weakened rapidly to enter a neutral phase with surface temperatures in the Nino-areas of the pacific now well within the range of plus/minus 0.5°C from the average.
There was however some rain in the last few days of April 2021 over the central to eastern parts of the country, ranging from zero to about 50mm. Areas or districts with the highest falls were Richards bay in KZN (50mm), Queenstown (50mm) and Elliot (40mm) in the Eastern Cape, Kroonstad (31mm), Ventersdorp (30mm), Kimberley (30mm), Fouriesburg (30mm) and Koppies 30mm.
Heavy rainfall of up to 300mm resulted in localised flooding in the first week of May over parts of the Southern Cape. Up to 80mm occurred in the drought-stricken Langkloof and more than 100mm in the Bonnievale area. Very little or no rain occurred over the still drought-stricken southern parts of the Eastern Cape.
The drier conditions over the summer grain areas are welcomed to speed up the harvesting process of soya and dry beans, ground nuts, sunflower and early planted maize. The lack of rain in the March and April period was very negative for veld conditions because grasses and other plant dried out very early, resulting in lower grazing quality. It can also increase the risk for early veld fires that can pose a serious risk for the winter and spring season with above average loads of combustible material.
Levels of nearly all larger storage dams in the central tot eastern parts of the country are still at favourable levels with average levels in the Free State 98.8%. The most significant improvement in levels were in Limpopo where the average levels are now at about 86.8% compared to 70% last year the same time. The Tzaneen dam increased from about 10% a few months back to more than 100% currently.
Storage dams in the central to southern parts of the Eastern Cape is at disastrous low levels with the Kouga dam at 4.4% and Impofu dam at 15% – the main water sources of the Nelson Mandela Metro and surrounding irrigation areas. The Bridle drift dam supplying water to the Buffalo City Metro is at about 28%. It is expected that the rain in the first week of May in the Eastern Cape can result in some water reaching the larger storage dams like Kouga.
Most of storage dams in the Western Cape are at healthy levels for this time of the year before the start of the rainy season and are on average more than 10% higher compared to last year the same time. The Clanwilliam dam that is the most import dam supplying water to agriculture in the western parts of the Western Cape, is at only 15.8%.
The water level in Lake Kariba in Zambia increased to 49.8% compared to 28.8% last year the same time while the Katze dam in Lesotho increased to 77% and the Mohale dam to 39%. The Hardap dam in southern Namibia was at the end of April 2021 at 68.6% of full volume.
ENSO and Indian Ocean
ENSO (El Nino Southern Oscillation)
Surface temperatures of most the Nino areas are well within the neutral range at the end of April 2021 with the exception of the Nino-1+2 areas (closest to South America) that is about 0.7°C cooler than normal and temporary La Nina like.
Forecasts indicate that the neutral state will most likely continue until at least September 2021. There is a split forecast between La Nina and Neutral of about 45% probability each for the early summer of 2021/22 with an only 10% probability of El Nino to occur. The probability change to about 50% La Nina and 40% Neutral from October 2021.
The Southern Oscillation Index (SOI) that is the atmospheric indicator of the ENSO, was at the end of April 2021 solidly neutral. On a scale from -30 (strong El Nino) to +30 (strong La Nina), the 30-day average was 2.69 on 11 May 2021.
Indian and Atlantic Ocean
Most of the southwestern Indian Ocean, south and south-east of the Africa coastline, still indicates cooler than normal sea surface temperatures although there was some warming during April. Surface waters of the west coast of South Africa, Namibia and Angola is however about 2°C to 4°C warmer than normal and is consistent with a so-called Benguela Nino. In 1985, 1995 and 2011 events caused severe disruption of the fishing industry with warmer waterless oxygen and migration of many fish species. It can also have an effect on weather patterns, especially towards the Namibian and Angolan coastlines but the global impacts are not clear.
The Indian Ocean Dipole (IOD) index remains in a neutral phase and forecasts are indicating that it remains for most of 2021 in a neutral phase.
Rainfall and Climate
Summer Rainfall Area
Very little further rain is expected for most of the Summer Rainfall Region up until about October 2021. Some rain is however possible in the Eastern Cape and southern parts of KZN in the last part of May.
Above average temperatures still occur over much of the interior up until the middle of May. A series of cold fronts in the last part of May can result in a sharp drop in temperatures over the central to southern parts. Very cold conditions are expected for mid to late winter.
First dates of frost are later than normal with very little frost until the second week of May. Frost is expected in the second part of May over the central to southern parts of the country and later this in June/July over the more northern parts.
Most winter months that followed La Nina events (like 2021) resulted in heavy snow falls. It is there for possible that heavy snow can occur in the last few days of May but more likely in the mid to late winter months.
Winter Rainfall Area
Rainfall outlooks improved for most of the Winter Rainfall Area for the next months. More than 20mm is expected between 15 and 17 May over parts of the Swartland with lighter falls over the Southern Cape. Rain is also expected between 20 and 22 May as well as on 25 and 26 May. Although the heavy rain in parts of the Southern Cape caused some damage to topsoil, was it however very beneficial for replenishment of soil water as well as surface water to dams.
The start to the winter crop season will be the best in many years due to the very wet conditions and further rainfall expected. The expected rain in the last part of May will also result in favourable conditions over the Swartland and adjacent areas. There is a possibility that the very dry north western interior of the Western Cape and parts of the south western Northern Cape can receive some winter rainfall.
Very little further rainfall is expected for the winter and spring. An unknown factor is the presence of the Benguela Nino that is a phenomenon of warmer waters off the coast of Namibia and Angola.
Summary and conclusion
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