The current La Niña phenomenon has reached maturity and will remain at La Niña levels until around April this year. Longer-term outlooks are still positive for more rain in February and March for most of the summer rainfall region. A short dry spell was predicted from around 16 to 21 January with further rain in the last week of January over the central to eastern parts.
Heavy rainfall has been occurring over the central to western parts of the country since the second half of December last year. Localised flooding occurred in Hoopstad and Wesselsbron in the Free State, Augrabies in the Northern Cape, parts of Gauteng, the southern parts of Namibia, and western and central parts of the Northern Cape.
Rainfall of more than 100mm per day occurred in these areas, resulting in heavy run-off and waterlogged conditions. Waterlogged soils are causing severe damage to crops in the north-western Free State in districts such as Bothaville, Wesselsbron, Viljoenskroon, Hoopstad, and adjacent districts in the North West such as Wolmaransstad and Bloemhof. Damage is also occurring in the eastern Free State in Bethlehem, Warden, Frankfort, and Heilbron.
Drought damage vs water damage
Serious drought damage occurred in Mpumalanga where early-planted summer crops have been in the sensitive reproductive stages. Permanent damage is already evident on maize and soya beans. However, there was rain between 11 and 13 January, which helped to stabilise conditions. Serious drought conditions remain prevalent in parts of the Eastern Cape in Jansenville, Steytlerville, and Willowmore.
Drought also persists in the Northern Cape districts of Vanwyksvlei, Loeriesfontein, Williston, and other adjacent districts where there was very little to no rain. These areas missed out on the heavy rainfall during the first week of January in the northernmost parts of the Northern Cape.
Grazing conditions rapidly improved in many parts of the Northern Cape, especially in the Kalahari. However, time and more rain are needed for a full recovery. Water levels of storage dams in the summer rainfall area are favourable, except for smaller dams in Limpopo. Tzaneen Dam is at 16,5% and Middle Letaba Dam at less than 1%.
The Vaal Dam level increased to 65% since the beginning of January this year, from a low of nearly 35% in December 2020. Dam levels in the Eastern Cape are also low with the Kouga Dam at 9,5% and the Bridle Drift Dam at 32,7%, both supplying water to Nelson Mandela Bay. Western Cape dams are at healthy levels, but they are rapidly dropping in the hot conditions.
The water level in Lake Kariba in Zambia is at 20,44%. The Katze Dam in Lesotho rapidly increased to 46% in the first week of January this year, from a low of 26% last December.
La Niña system reaches maturity
Sea surface temperatures in the El Niño areas have been at La Niña levels since the middle of August last year. The average temperature deviation of the important Niño-3,4 area is now 1,1°C cooler than usual after reaching a peak of 1,7°C in November last year. Forecasts indicated that the current La Niña reached maturity in December 2020, and it is not expected to intensify further. It will remain at La Niña levels until at least April/May this year.
The Southern Oscillation Index (SOI), which is a measure of the interaction between surface conditions in the Niño areas and overlying weather systems, is strengthening towards more intense La Niña levels. The SOI is currently at +19,42 on a scale of +30 (very strong La Niña) to -30 (very strong El Niño). This is the highest SOI value recorded since December 2011.
The Indian Ocean Dipole (IOD) index has already been in a neutral phase for the past weeks. It is currently precisely on the long-term average. The south-western Indian Ocean (east of the south coast of South Africa) is 2°C cooler than usual. However, some warming took place around Madagascar where temperatures are now between 0,5 and 1°C warmer than usual.
Approximately 60 to 70% of the total Indian Ocean was cooler than usual at the beginning of this year. Yet most parts of the Pacific and Atlantic oceans in the northern hemisphere are warmer than usual, resulting in a record number of hurricanes.
Increased chances of cyclone occurrences
Past La Niña weather events were usually associated with above-average rainfall from December to April. The 2020/21 La Niña also follows this pattern. With the warming of a part of the Indian Ocean around Madagascar in the past month, the area is more likely to produce cyclones – such as Eloise – and tropical depressions that can cause drier weather conditions over the central to western parts of Southern Africa and flooding over Mozambique and adjacent areas.
Short-term weather forecasts showed a drier spell from roughly 16 to 21 January with further rain during the last week of January over the central to eastern parts.
Longer-term outlooks are still positive for heavy rain in February, March, and April. However, it depends on whether cyclones will develop.
Flooding remains a possibility
Average to above-average daytime temperatures can be expected for the rest of January and the first part of February. Above-average minimum temperatures can be expected due to the moisture-rich lower atmosphere caused by the rain, trapping energy closer to the earth’s surface.
Owing to very strong summer rainfall systems, summer rainfall is still possible, especially over the central to south-eastern parts of the winter rainfall region. There is a high probability for a late start to the real winter rainfall season.
Short- to medium-term outlooks indicate high temperatures with the possibility of some rain in the first week of February over the Southern Cape. Drier conditions were also possible from 16 to 21 January, except for the north-eastern parts. Heavier rainfall is possible during the last week of January, except for the southern and south-western parts.
Longer-term weather outlooks remain positive for further heavy rainfall in the second part of February and March this year, with the possibility of flooding.
A final thought
Flooding and waterlogged conditions caused damage to summer crops in the Free State and adjacent areas, but drought resulted in damage in parts of Mpumalanga. Most of the Northern Cape’s drought-stricken areas received rain, except the southern parts.
La Niña reached maturity but will remain a fully fledged La Niña until at least April this year. Short-term weather outlooks indicated a short dry period from 16 to 21 January, with heavier rainfall over the central to eastern parts in the last week of January. The risk for flooding remains exceedingly high for the next few months. – Johan van den Berg, independent agricultural meteorologist