Climate and agricultural conditions – April 2021
- La Nina weakened rapidly in March resulting in less favourable summer rainfall conditions but improved conditions for winter rainfall in the south western parts of the country. Rain in Summer Rainfall area still possible in the last week of April.
- Severe drought still threatens lively hoods in parts of the Eastern and Northern Cape with farmers now also are suffering a locust outbreak over a very extended area.
Sporadic rainfall occurred about country wide in March and first part of April 2021 with heavy falls over smaller areas in nearly all Provinces. The best falls occurred in districts and areas like Frankfort in the Free State with more than 100mm, Kathu in the Northern Cape with more than 90mm, Lichtenburg 120mm, Mooivier in KZN with about 80mm, Pretoria 80mm, Twee Rivieren in Kgalagadi 80mm, Bloemfontein 75mm, Postmasburg 50mm, Bethlehem 60mm and Tosca near Vryburg with 55mm. Lighter falls also occurred over the drought stricken southern parts of the Northern Cape with Prieska 40mm,Van Wyksvlei and Noupoort 15mm and parts of Kenhardt/Pofadder with 20mm.
Very little or no effective rainfall occurred in the very dry Eastern Cape and surrounding areas in the Western Cape. Districts with disaster drought conditions include Willowmore, Uniondale, Steytlerville, Jansenville, Patensie, Kirkwood and Paterson. Most of the irrigation areas in the Langkloof, Sondagsrivier and Gamtoos Valleys that are important fruit and citrus growing areas, suffered from a lack of water with storage dams empty or very close to empty. The Gamtoos Valley irrigation depends on the Kouga dam for water and the dam level is already for the past two seasons close to or less than 10% of full capacity.
One of the other major issues threatening live stock and even irrigation farmers in the Northern and Eastern Cape as well as adjacent Free State and Northwest Province, is the presence of a locust outbreak. Sufficient rainfall with frequent falls occurred in parts of the Karoo and Kalahari that enables breeding of new locust generations. Most of the Eastern Cape in areas like Graaff Reinet, Aberdeen, Middelburg and in the Northern Cape from Upington northwards to the border of Botswana are suffering from large outbreaks. This very vulnerable drought stricken areas are now suffering from the locust outbreak that can have a more devastating effect on grazing and financial conditions. This outbreak is expected to last until at least the first frost that is expected in May.
Levels of nearly all larger storage dams in the central tot eastern parts of the country are at very high levels with dams in the Free State still at 99.9% on average with the Vaal dam still at 105%. Dams in the Western Cape are at the end of the dry season still on average at levels above 50% that is more than 12% better compared to last year the same time. The main concern is the rapidly drop of water levels in the important Clanwilliam dam that is currently at less than 25%, dropping by about 3% to 4% per week. Storage dams in the central to southern parts of the Eastern Cape is at disastrous low levels with the Kouga dam at 5% and Impofu dam at 15% - the main water sources of the Nelson Mandela Metro and surrounding irrigation areas. The Bridles drift dam supplying water to the Buffalo City Metro is at about 30%.
The water level in Lake Kariba in Zambia increased to 46.5% compared to 18.4% last year the same time while the Katze dam in Lesotho increased to 79% and the Mohale dam to 40%. The Hardap dam in southern Namibia was at the end of March 2021 at 70.8% of full volume.2. ENSO and Indian Ocean
2.1 ENSO (El Nino Southern Oscillation)
Surface temperatures of all the Nino areas were on the border between La Nina and Neutral in the first week of April 2021. There was again a slight strengthening towards La Nina since previous weeks but it is likely to be only temporary. All other indicators indicate a Neutral phase to last through autumn and most of the Southern Hemisphere winter.
The Southern Oscillation Index (SOI) that is the atmospheric indicator of the ENSO, rapidly fell from SOI positive (La Nina) to SOI neutral in March, causing a rapidly falling phase of the SOI. On a scale from -30 (strong El Nino) to +30 (strong La Nina), the 30-day average SOI fell from +15.85 in January and +11.32 in February to -0.46 at the end of March 2021.
Longer term forecasts favour a return to La Nina (50% probability) or neutral (40%) levels from about August/September with a very low probability for the development of El Nino (10%).
2.2 Indian Ocean
Most of the south western Indian Ocean, south and south east of the Africa coastline, indicates cooler than normal sea surface temperatures. Warmer surface waters developed northwards in the past two months, resulting in a higher incidence of tropical depressions in and around the Mozambique Channel as well as east of Madagaskar. Significant cooling started to occur over large parts of the southern Indian Ocean and well as south eastern parts of the Atlantic Ocean towards the African south west coast during March. This can have an impact on the intensity of the winter as was the case in 2020.
The Indian Ocean Dipole (IOD) index remains in a neutral phase. Although forecasts for Indian Ocean surface temperatures are very volatile, are there indications of a return to negative index values of the IOD in the second part of winter.3. Rainfall and Climate
3.1 Summer Rainfall Area
The rapidly falling phase of the SOI that is associated with a weakening of the current La Nina episode in March, also have a negative impact on rainfall outlooks for autumn and winter for the central to eastern parts of the country. The falling phase is usually a positive signal for rain over the south western parts of the country, including the west coast and adjacent interior of the Northern and Western Cape.
With the possible return to La Nina conditions and relative favourable Indian Ocean surface conditions from about August 2021, is it very possible for further favourable rainfall conditions for the 2021/22 summer season.
Warm temperatures are expected for the most of April. With the possible recurrence of colder than normal surface temperatures in the south western Indian Ocean and Atlantic Ocean south and south west of Cape Town, is a very cold winter from about the middle of May 2021 very possible.
First dates of frost are anticipated in the first to second week of May for the southern and south eastern half of the country and towards the end of May for the more northern parts.
3.2 Winter Rainfall Area
Very little or no rain is expected for most of the Western Cape for the rest of April but cold fronts are likely to have an impact from about May. Normal to above normal rainfall is likely in the first part of winter over the south western parts, shifting eastwards to the Southern Cape in the second part of winter. At this stage is a severe drought not anticipated. Most La Nina events in the past resulted in positive rainfall outlooks for the second part of the winter that is very positive for winter grain production.
Forecasts still favour some rain in the next three months with tropical moisture still present over West Africa. With expected favourable Indian Ocean temperatures and the lack of an El Nino for 2021/22, are average to above average rainfall also a high probability for 2021/22.4. Summary and conclusion
- Rainfall outlooks for the Summer Rainfall Area weakened, mainly due to the weaker La Nina episode. A recurrence of very cold conditions in winter are possible due to the colder than normal Indian and Atlantic Oceans.
- The probability for neutral to La Nina conditions for 2021/22 is about 90% with an only 10% probability for an El Nino event.
- Rainfall conditions improved for the south western Cape and West Coast areas and adjacent interior for the early parts of winter. Rainfall outlooks are also positive for the second part of winter, shifting towards the Southern Cape.
6. Contact detail
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