Important Issues
Uncertainty about rainfall for rest of the summer season remains high.
Early frost poses a risk to the maize crop, especially in the northwest Free State.
1. Current conditions
Rain occurred over the eastern summer crop production areas towards the end of the planting window for maize and soya beans in November 2018. Rain over the central to western summer crop areas only started to occur just before the end of 2018. This was already past the planting window for maize and the crop was in general planted about one to two weeks after the close of the “acceptable” planting window. This is posing a high risk for early frost damage. If frost occurs before the end of April, damage to the crop will be eminent. It is estimated that about 70-80% of the maize planted towards the west of the N1, is planted after the close of the acceptable planting window and is probably close to 50% of the total maize crop that will be planted.
There is still time until about the last week of January 2019 to plant sunflower seed in the central to western production areas.
Another feature of the season is the occurrence of very stormy weather with strong winds and large hail associated with heavy falls of rain over localised areas. Examples are the storms that hit Sun City, Bela-Bela, Middelburg, Reitz, Ventersdorp and areas to the west of Johannesburg.
Light falls of rain still occurred over the Western Cape, especially towards the South Coast. This is untimely for this time of the year, indicating the absence of “normal” weather patterns this season.
The far western and south western parts of the country are still suffering severe drought conditions.
Although surface water conditions are in most areas better compared to last year, is the situation of subsurface water from boreholes becoming very critical. Water replenishment only took place as far back as the 2010/11 season with below average rainfall in many areas since then with very little water draining into deeper layers of the soil.
2. El Nino and Indian Ocean
The 2018/19 season will probably be remembered as one of the most difficult seasons in terms of rainfall forecasts. It is partly due to a very volatile set up of sea surface temperatures in both the Indian and Pacific Oceans. El Nino conditions in terms of sea surface temperatures exceeded limits only in October 2018 following earlier forecasts of a much earlier development. At the end of December 2018 there was still no coupling of El Nino and weather systems with the Southern Oscillation Index still on the La Nina side of Neutral. Looking at the setup of sea surface temperatures in the Pacific, is there a large pool of cooler than normal sea surface temperatures just to the south of the Nino-areas. It is possible that this pool may disturb the normal effect of El Nino or neutralize the effect. https://www.longpaddock.qld.gov.au/seasonal-climate-outlook/sea-surface-temperature/. The latest indications are that El Nino has probably reached its peak and can start to decay but we know from experience that there are phases of development that can strengthen again. Bottom line indicates still a high level of uncertainty.
The Indian Ocean also showed huge spatial variation with cooler than normal sea surface temperatures on the west coast of Australia but warmer water in the central to western Indian Ocean, reaching the positive phase of the Indian Ocean Dipole (IOD) Index. A positive IOD is negative for rainfall over Southern Africa. The IOD weakened since November and is now in a neutral phase.
3. Expected rainfall and temperature conditions
3.1 Summer Rainfall Areas
3.1.1. Rainfall
Short term forecasts are showing improved probabilities for rainfall from about 15 to 23 January over most of the country, except for the western and south western parts of the Northern Cape and western parts of the Eastern Cape. There is a very high level of uncertainty about expected rainfall for the rest of the summer season.
There are two scenarios in terms of the current season forward with estimated probability of occurrence:
Western parts of the country (roughly to the west of the N1), excluding the far western half of the Northern Cape and western parts of the Eastern Cape:
Average rainfall for the rest of January and first part of February with dry conditions in the last part of the season with the effect of El Nino that comes into play (70% probability).
El Nino reaction not typical or can weaken rapidly. Good rainfall for rest of the season. (30% probability). Compare 1987/88.
Eastern parts (east of N1):
Average rainfall for the rest of the season until end of March. El Nino effect not severe to the east (70% probability).
Below average rainfall for February and March (30% probability).
3.1.2 Frost
Analysing frost dates for different areas, there is an about 40% probability for light frost in the Northwest Free State (Bothaville) before 10 April and 20-30% probability for moderate to severe frost between 20 and 30 April. The risk is much lower towards the north western production areas (Lichtenburg) where there is only about a 10% probability for moderate to severe frost before 30 April. Frost occurred as early as about 20 March in 2007 but as late as end of May in 2016.
3.2 Winter Rainfall Areas
Some light falls of rain still possible with cold fronts still visiting the southern tip of the country. It is especially towards the South Coast where rain is possible in the next weeks.
3.3 Namibia
The same scenarios apply for Namibia as for the Western parts of the South Africa under 3.1.1 above. The southern parts of Namibia may be added to the western parts of the Northern Cape where prospects for rain in coming months are poor.
4. Summary and conclusions: bullet Rainfall and agricultural conditions improved with some rain in the last week of December and first part of January but rainfall was very patchy. Very little or no rain to the extreme western parts. A high risk for unfavourable rainfall conditions for the western half of the country.
High level of concern about livestock grazing conditions, especially the western parts of the country.
Frost poses a real risk for the maize crop that is planted very late.
El Nino development and effect on climate remains very uncertain. Some indications that El Nino already reached a peak.
Johan van den Berg Santam.
