1. Current conditions
Extreme high temperatures with heat wave conditions continued to occur over large parts of the country. Isolated rainfall associated with hail occurred over Mpumalanga, KZN, Limpopo and parts of the eastern Free State in the past two weeks. The current extent of hail damage is the most severe in at least the last decade.
Summer crops planted in the central to western parts are suffering from the extreme heat conditions, especially the very late planted crops where plants are still very young. The very hot and dry conditions are also prevented the planting of sunflower seed. It is now too late to plant sunflower because the last acceptable planting dates are towards the third week of January in the western production areas.
Poor grazing conditions, very low meat prices and a lack of demand is now responsible for a disaster developing for many livestock farmers, especially in the central and western parts of the country and most of Namibia.
2.El Nino and Indian Ocean
El Nino conditions weakened rapidly since the second part of December 2018 and are now in the neutral range or just outside the neutral range. The average sea surface temperatures in the important Nino3.4-area were 0.5°C warmer than normal in the third week of January 2019 that is on the borderline neutral.
The Southern Oscillation Index (SOI) also remained neutral to even La Nina like in the past few months, not reflecting El Nino conditions.
On the other hand is the flooding in the southern parts of South America typically El Nino associated.
Some rewarming is taking place in the central to eastern (Australian west coast) Indian Ocean but cooling has taken place over the western Indian Ocean (near Madagascar) and that is good news. The Indian Ocean Dipole Index (IOD) is also now in the neutral range.
3. Expected rainfall and temperature conditions
3.1 Summer Rainfall Areas
3.1.1. Rainfall
Short to medium term rainfall probabilities now started to reflect more the effect of the neutral conditions in the Nino areas with improved rainfall probabilities over most of the Summer Rainfall Area. February and March are historically the dominant rainfall months for the central to western parts of the country and it seems that there is a high probability for that to occur in 2019.
There is now a sharp positive change in the outlook for the rest of the summer season with improved probabilities for rainfall:
Western parts of the country (roughly to the west of the N1), excluding the far south western parts of the Northern Cape:
Average rainfall for February with continued dry conditions in the last part of the season due to some remnant effects of the weak El Nino-conditions that occurred (30% probability).
Neutral Nino and Indian Ocean conditions dominating with average to above average rainfall for rest of the season (70% probability).
Uncertainty if the drought stricken south western parts of the Northern Cape and adjacent Western Cape will benefit from the improved prospects for rain for the rest of the Summer Rainfall Area.
Eastern parts (east of N1): Average to above average rainfall for the rest of the season until end of March (70% probability).
Below average rainfall for February and March (30% probability).
3.1.2 Frost and heat units
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.
With the better rainfall conditions expected in February and even March is the risk for frost smaller. On the other hand can rain and less heat units be responsible for a lower growth rate that can have consequences for the very late planted crop. If minimum temperatures drop below 10°C then the growth rate of a crop like maize decreases rapidly. Analysing minimum temperatures can the following areas expect lower growth rates from the following dates:
Locality Average date with minimum temperatures for 10 consecutive days <10°C First date with minimum temperatures for 10 consecutive days <10°C
Lichtenburg 27 April 08 April
Bothaville 20 April 05 April
Bethal 10 April 24 March
Bethlehem 09 April 20 March
Although frost dates may occur late, is the effect of a lower growth rate important. For a place like Bothaville is the average date when minimum temperatures below 10°C occur for more than 10 consecutive days about 20 April and the earliest date 5 April. With planting dates of early January is it evident that the growth rate will decrease before the end of the development cycle of about 120 days and before the end of April for Bothaville.
3.2 Winter Rainfall Areas
With improved rainfall conditions over the Summer Rainfall Area is it likely that rainfall outlooks will decrease over the south western Cape but rain is still expected over the Southern and Eastern Cape from summer rainfall systems.
3.3 Namibia
The same scenarios apply for Namibia as for the Western parts of the South Africa under 3.1.1 above. Outlooks for rain improved for the central to northern parts compared to previous forecasts. The southern and south western 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 Positive news is that conditions for rainfall for at least the month of February improved for most of the Summer Rainfall Area.
It now seems that El Nino already reached a peak. Uncertainty about the rest of 2019.
Santam- Johan van den Berg.
