December 2017 started with good rainfall over most of the summer rainfall region, with Mpumalanga and northern KwaZulu-Natal receiving more than 50 mm during the first 10 days of the month, while the second 10 day period of the month followed the same trend with rains... Read more
December 2017 started with good rainfall over most of the summer rainfall region, with Mpumalanga and northern KwaZulu-Natal receiving more than 50 mm during the first 10 days of the month, while the second 10 day period of the month followed the same trend with rains over most of the summer rainfall region. Major damage, however, was caused by storms around the Vaal Dam area, with reports of a tornado over the Vaal Marina. Over the northern parts (Limpopo, North-West, Gauteng & Mpumalanga), the last good rain fell between the 12th and 13th, while the northern Cape, Free State, and parts of the Western and Eastern Cape received good rainfall between 13 and 18 December.
Northern and Eastern Cape, as well as Free State received good rains during the last 10 days of December. By the end of the month, the rainfall trend shifted northward towards Gauteng, Mpumalanga, Limpopo and North West Provinces.
Another major storm caused damage over parts of Johannesburg with reports of another tornado - trees were uprooted - and hail over the southern parts of Gauteng.
The promise of a good rainfall month for the whole summer region proved to be empty as rainfall was mostly scattered over the northern and western summer rainfall region. Only the northern Free State, Gauteng, Mpumalanga and northern KwaZulu-Natal received above normal rainfall during December.
Good rainfall - more than 80 mm - fell over large parts of the summer rainfall region, most notably Gauteng, Mpumalanga, KwaZulu-Natal and the northern Free State.
Figure 1: Total rainfall estimation in millimetres for 1 to 31 December 2017
Figure 2: Percentage difference - rainfall for 1 to 31 December 2017.
Figure 2 supplies perspective for December. Areas that received above normal rainfall are indicated in green and blue. Isolated areas over the Northern Cape and southern Free State received above normal rainfall, while the highest rainfall fell over the northern Free State, Gauteng, Mpumalanga and northern KwaZulu-Natal. Below normal rainfall fell over Limpopo and the North-West. Good rainfall is needed over these areas for the rest of the rainfall season to avoid drought conditions developing.
Figure 3: Cumulative rainfall from 1 July 2017 to 31 December 2017 in millimetres.
This cumulative rainfall map (Figure 3) for 1 July to 31 December highlights the areas that received more than 150 mm during the period: Light green indicates areas receiving between 150 and 200 mm; dark green indicates areas receiving between 200 and 300 mm; and areas that received more than 400 mm, are indicated in blue.
Figure 4: Percentage difference - rainfall for 1 July to 31 December 2017.
Figure 4 highlights those areas that received below-normal and above-normal rainfall during the last 6 months. Yellow to light brown show areas of concern, while isolated areas throughout the country highlighted in green, received above normal rainfall during the last 6 months. Only Gauteng and large parts of Mpumalanga have received above-normal rainfall, while the rest of the summer rainfall region received 50 to 75% of their normal rainfall so far this season.
El Nino/La Nina
Background: Periods of below normal rainfall in South Africa are often linked with the El Nino event while above normal rainfall is linked to La Nina. The latest predictions issued by the Australian Bureau of Meteorology indicate neutral conditions (Figure 5). Possibility of La Nina conditions developing January 2018. Normal to above-normal rainfall is expected for the summer rainfall region during the 2017/18 rainfall season.
Figure 5: Current model predictions for Sea Surface Temperature in the Pacific.
Figure 6: ProbaV difference map for November 2017 compared to the long-term (19-year) average.
Figure 6: This map is created by calculating the difference between December 2017, and the long-term (20-year) average for December - showing dominant normal vegetation activity (beige). Areas of concern with below-normal vegetation activity (red) include the southern Free State, the eastern parts of Limpopo, Mpumalanga and isolated areas of North West.
Figure 7: Percentage of Average Seasonal Greenness for the last 6 months ending in December 2017.
Drought is a long-term phenomenon. Focusing on longer time-periods is a more reliable method to monitor and map drought. Areas of concern include the Western Cape, western Eastern Cape, western & southern Northern Cape and the Free State. Conditions remain neutral over the summer rainfall region but these conditions could change with continued summer rains.
Figure 8: South African dam levels between December 2017 and January 2018
Rainfall over South Africa was erratic in December with some areas experiencing below-average rainfall. In the western Free State and North West rains have been had been sporadic and many farmers have had to plant maize later than usual.
In the eastern summer planting area, including Mpumalanga, most farmers have planted as normal, but are now desperate for follow-up rain to replenish soil moisture levels; this is critical because many maize crops will soon be in the "silking" stage of growth and water stress can reduce final yields significantly. Hopefully, the La NiÃ±a weather pattern could result in rains in the second half of January.
The drought persists in the Western Cape. The Western Cape Department of Agriculture is providing a service based on satellite technology (from a Dutch company, eLeaf) which indicates the efficiency of irrigating various crops. Satellite data shows the continual production of biomass (indicator of production) in relation to the water requirements of a specific crop. It is then possible to determine if the crop is currently being under-watered or over-watered and to estimate the future water needs of the crop in the short-term; this has improved the efficient use of water and yields by up to 10% in apples.
With hot conditions prevailing, livestock farmers are cautioned to keep an eye on their animals for heat stress. High producing animals, such as dairy cattle, are especially vulnerable, however all animals are susceptible when temperatures are very high. High humidity levels will exasperate the situation as will drought conditions when water availability is limited. A further risk for all livestock farmers during hot and dry conditions is fire. The risks are particularly high in the Western Cape areas.
Severe storms easily displace animals as well as damages infrastructure causing both structural and livestock losses. Farmers should always keep an eye out for severe weather warnings and prepare in advance for them as much as possible. For the summer rainfall regions receiving good rains and high temperatures, problems with intestinal roundworms can be expected to increase. Farmers should do regular observations and look out for signs of bottle jaw and anaemia (Famacha system) and high faecal egg counts. Treatment efficiency should be evaluated as many parasites are resistant to most active ingredients. A programme can be discussed with a vet.
SPOT Vegetation Data: The product was generated by the land service of Copernicus, the Earth Observation program of the European Commission. The research leading to the current version of the product has received funding from various European Commission Research and Technical Development programs. The product is based on VEGETATION data ((c) CNES).
PROBA-V Data: The product was generated by the land service of Copernicus, the Earth Observation program of the European Commission. The research leading to the current version of the product has received funding from various European Commission Research and Technical Development programs. The product is based on PROBA-V data ((c) ESA).
El-Nina/La Nina predictions: POAMA graph provided by courtesy of the Australian Bureau of Meteorology, (c) 2016.
Rainfall Estimation (RFE): Data provided by the National Oceanic and Atmospheric Administration (NOAA), Centre for Weather and Climate Prediction. http://www.cpc.noaa.gov/...
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