Important Issues
La Nina reached maturity and will remain at La Nina levels until about April 2021.
Longer term outlooks are still positive for further rain in February and March for most of the Summer Rainfall Region. A short drier spell is possible from about 16 to 21 January with further rain in the last week of January over the central to eastern parts.
1. Current conditions
Very heavy falls of rain started to occur over the central to western parts of the country since the second part of December 2020. Localised flooding occurred in areas like 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 amounts of more than 100mm per day occurred in these areas, resulting in heavy runoff and water-logged conditions. Water-logged soils are starting to cause severe damage to crops in the north western Free State in districts like Bothaville, Wesselsbron, Viljoenskroon and Hoopstad and adjacent districts in the Northwest Province like Wolmaranstad and Bloemhof. Damage are also occurring in the eastern Free State in Bethlehem, Warden, Frankfort and Heilbron.
Serious drought damage occurred in Mpumalanga where early planted summer crops are in the sensitive reproductive stages. Permanent damage is already evident on maize and soya beans but rain occurred between 11 and 13 January that can help to stabilise conditions. Serious drought conditions remain prevalent in parts of the Eastern Cape in areas like Jansenville, Steytlerville and Willowmore.
Drought also continues in districts of the Northern Cape like Vanwyksvlei, Loeriesfontein, Williston and other adjacent districts where very little or no rain occurred because these areas missed out on the rainfall event in the first week of January that caused heavy falls in the more northern parts of the Northern Cape.
Grazing conditions rapidly improved in many parts of the Northern Cape especially in the Kalahari but time and more rain is needed for full recovery.
Water levels of storage dams in the Summer Rainfall Area are favourable except for smaller dams like in Limpopo with Tzaneen dam on 16.5% and Middle Letaba with less than 1%. The level of the Vaal dam increased to 65% since the beginning of January 2021 from a low of about 35% in December 2020. The levels of dams 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 the Nelson Mandela Metro. Western Cape dams are at healthy levels but levels are dropping rapidly with the hot conditions that are experienced.
The water level in Lake Kariba in Zambia is at 20.44%. The Katze dam in Lesotho rapidly increases to 46% in the first week of January 2021 from a low of 26% in December 2020.
2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
Sea surface temperatures in the Nino-areas are constantly at La Nina levels since about the middle of August. The average temperature deviation of the important Nino-3.4-area is now at 1.1°C cooler than normal after reaching a peak of 1.7°C cooler than normal in November 2020. Forecasts indicated that the current La Nina reached maturity in December 2020 and it is not expected to intensity further. It will remain at La Nina levels until at least April/May 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, is strengthening towards more intense La Nina levels. The SOI is currently at +19.42 on a scale from +30 (very strong La Nina) to -30 (very strong El Nino). This is the highest SOI value since December 2011.
2.2 Indian Ocean
The Indian Ocean Dipole (IOD) index is already for a recent past weeks in a neutral phase and currently exactly on the long-term average. The south western Indian Ocean (east of the South Coast of South Africa) is about 2°C cooler than normal but some warming took place around Madagascar where temperatures are now between 0.5°C and 1°C warmer than normal. About 60% to 70% of the total Indian Ocean was at the beginning of 2021 cooler than normal but most of the Pacific and Atlantic Oceans in the Northern Hemisphere are warmer than normal, resulting in a record number of hurricanes.
3. Rainfall and Climate
3.1 Summer Rainfall Area
La Nina-events in history were usually associated with above average rainfall in the December to April period. The 2020/21 La Nina is also following this pattern. With warming of a part of the Indian Ocean around Madagascar in the past month is the area more likely to produce cyclones and tropical depressions that can cause drier conditions over the central to western parts of Southern Africa and flooding over Mozambique and adjacent areas.
Short term forecasts show a drier spell from about 16 tot 21 January with further rain in die last week of January over the central to eastern parts.
Longer term outlooks are still positive for heavy rain in February as well as March and April. It will however all depends on whether cyclones will develop.
Temperature
Average to above average daytime temperatures can be expected for the rest of January and 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 surface of the earth.
3.2 Winter Rainfall Area
Due to very strong summer rainfall systems is summer rainfall 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.
3.3 Namibia
Drier conditions are also possible from about 16 to 21 January except for the north eastern parts. Heavier falls of rain are again possible in the last week of January except for the southern and south western parts.
Longer term outlooks are still positive for further heavy falls in the second part of February as well as March 2021 with a possibility of flooding.
4. Summary and conclusion
Flooding and water-logged 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 drought-stricken areas of the Northern Cape received rain except the southern parts.
La Nina reached maturity but will remain a full fletched La Nina until at least April 2021.
Short term outlooks indicate a short dry period from about 16 to 21 January with heavier falls of rain again possible over the central to eastern parts in the last week of January. The risk fort flooding remains very high in the next months.Sponsored by Santam Agriculture -Johan van den Berg -Independent Agricultural Meteorologist (M.Sc Agric, Agricultural meteorology, UFS)
