Important Issues
La Nina started to weaken but will remain at La Nina levels until about April 2021.
Rier spell is expected for most of February over the central to western parts that will be welcomed by most summer grain farmers. Heavy rains is still expected again March 2021.
Current conditions
Very heavy falls of rain were measured over the central to eastern parts of the country in the second part of January and first week of February. Falls of more than 100mm of rain per 24-hour period were recorded in several areas, resulting in flood conditions. Water levels in rivers like the Lower Orange River rose to levels last seen in 2011. Areas most seriously affected were the western, southern and southwestern Free State and adjacent parts of the Eastern Cape in towns like Hoopstad, Wesselsbron, Bloemfontein, Trompsburg, Aliwal North and Lady Grey; central to north eastern parts of the Northern Cape in districts like Kuruman, Kathu, Vaalharts and Daniëlskuil. Very heavy falls also occurred in the northern and north western parts of Limpopo in areas like Vaalwater and Lephalale. Localised flooding and very wet conditions were also reported in the Eastern Free State in areas like Reitz and Frankfort. Following a very dry spell in Mpumalanga in the first part of January, heavy falls also occurred in these areas due to remnants of tropical storm Eloise at the end of January and first part of February.
Severe drought conditions are still prominent in the southern, south western and north western parts of the Northern Cape in districts like Williston, Van Wyksvlei, Carnavon, Calvinia and Loeriesfontein as well as parts of the western Kalahari like Askham and Noenieput. Extreme drought conditions continue in the western and central parts of the Eastern Cape in districts like Aberdeen, Willowmore, Uniondale, Steytlerville, Jansenville, Kirkwoord, Riebeeck Oos and Port Elizabeth. Most of the Langkloof between George and Kareedouw also received very little rain in recent months.
The summer grain crop suffered damage in areas like the north western and eastern Free State and smaller areas in other Provinces. On the contrast are there areas in especially the Northwest Province and parts of the Free State and Mpumalanga where record yields are expected. The expected drier conditions for February will assist in stabilizing or increase yields where water logged conditions occurred and push yields up to potential record yields in areas where less damage occurred and sufficient fertiliser was applied.
Grazing conditions recovered remarkable well in areas where follow up rain occurred. Problems with animal diseases are starting to cause problems and will likely increase in the next two months with lots of standing free water, causing ideal conditions for insects like mosquitoes and midgets to multiply.
Levels of storage dams are very high and nearly all larger storage dams in the central tot eastern parts of the country are overflowing. Dams like the Gariep reached levels of more than 120% at the end of January 2021 with the Vaaldam reaching full capacity on 8 February 2021. The Tzaneen dam increased to about 50% after being still at levels of less than 10% in December 2020.
The water level in Lake Kariba in Zambia is still less than 30% while the Katze dam in Lesotho rapidly increases to over 65 % in the first week of February 2021 from a low of 26% in December 2020. The Hardap dam in southern Namibia was at the end of January 2021 at 72% of full volume.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
All Nino-areas recorded a rise of about 0.2°C in sea surface temperatures in the last week of January 2021 according to the Australian Bureau of Meteorology (BOM). This is an indication that the current La Nina phase is now starting to weaken. It will however remain at La Nina-levels until at least April 2021.
The Southern Oscillation Index (SOI) that is a measure of the interaction between surface conditions in the Nino-areas and over lying weather systems, remains at relative moderate to strong La Nina levels. The SOI is currently at +13.95 on a scale from +30 (very strong La Nina) to -30 (very strong El Nino).
ENSO usually returns to neutral levels from about April to August. Current forecasts favour a return to La Nina of at least neutral levels for the 2021/22 summer with a low probability for El Nino. This is an indication for favourable rainfall conditions to continue in 2021/22 over the Summer Rainfall Area of Southern Africa.
2.2 Indian Ocean
Most of the Indian Ocean showed cooler than normal sea surface temperatures at the end of January 2021 with the exception of a small area of warmer than normal water around and south east of Madagascar. The extent of cooling in the Indian Ocean is unique considering the last at two decades where is was mainly warmer than normal.
The Indian Ocean Dipole (IOD) index remains in a neutral phase and forecasts indicates that it will remain neutral or negative (cooler than normal in the western Indian Ocean) for the next at least six months.
3. Rainfall and Climate
3.1 Summer Rainfall Area
The La Nina of 2020/21 reacts “normal” in terms of rainfall with heavy falls and flooding over parts of the Summer Rainfall Area because that is the typical impact of La Nina on rainfall. There are still smaller areas that did not receive the rainfall as expected during La Nina.
Short term outlooks are indicating a dryer spell for most of February over the central to western parts of the country. Tropical storms around Madagascar can be responsible for heavy rains over Mozambique, Madagascar and even inland over Zimbabwe, Zambia and north eastern parts of South Africa in the next two to three weeks.
Longer term outlooks remain positive for heavy rain in March, especially the second part of March over most of the Summer Rainfall Area.
Temperature
With less rain expected in the next few weeks will temperatures be warm but hot over the western interior. The higher temperatures will assist in improved growing conditions for the summer grain crop that suffered less heat units and less energy from the sun in recent past weeks.
3.2 Winter Rainfall Area
Very little or no rain is expected for most of the Western Cape for at least the next two to three weeks with the exception of light rain possible around 20 February. With the current La Nina phase becoming neutral from about April can it result in a late start to the normal winter rainfall season.
3.3 Namibia
In contrast to South Africa is rain possible in the next weeks, especially over the northern parts. Falls of more than 50mm can be expected over the northern parts until the last week of February. Very little rain is expected over the southern parts.
4. Summary and conclusion
Heavy falls of rain, consistent with “normal” La Nina impacts occurred over the central to eastern interior since the last part of January with flooding in some areas.
The current La Nina event is now starting to weaken but will remain at La Nina levels until at least April.
A drier spell is expected for most of the Summer Rainfall Area for most of February (exception of far north eastern parts) but heavier falls can be expected again in March 2021.
Johan van den Berg -Independent Agricultural Meteorologist -(M.Sc Agric, Agricultural meteorology, UFS)
