Climate and agricultural conditions - July 2020

Important Issues:

• Rain in the Winter Rainfall Area at the end of May enables farmers to plant winter crops at the end of the optimum window. Medium term outlooks for rain are not positive.
• Possible development of La Nina and Negative Indian Ocean Dipole (IOD) in coming months are positive for summer rainfall.

Current conditions

Above average rainfall conditions in the last part of summer and autumn assisted in favourable summer crop production conditions in the central to western parts of the summer cropping area. The rain in late March and April also alleviated drought conditions in the eastern production areas like the eastern Free State and Mpumalanga and prevented major drought damage although severe damage occurred in smaller areas. The soya bean harvest has been completed and about average yields were reported with areas like Koppies in the northern Free State and adjacent districts where above average yields were reported. The late arrival of severe frost also assisted in late plantings to reach maturity. Less hail damage compared to 2018/19 also occurred.

Severe drought in the Western Cape hampered plantings of winter crops but falls more than 30mm since 25 May improved conditions and will enable farmers to plant, although at the end of the optimum planting season or even a bit too late.  

Severe drought continues over most of the western to south western parts of the country as well as parts of the Eastern Cape.  Severe drought conditions also remain prevalent in the southern parts of Namibia but average to above average rainfall occurred since December 2019 over the central to northern parts of Namibia resulting in very favourable maize yields and recovery of grazing conditions and water resources.

State of storage dams in Southern Africa are in general favourable except for some burning areas where rainfall was insufficient to replenish dams. The biggest hot spot currently is the level of the Vaaldam where the level dropped below 50% with the next rainy season at least 6 months away. The water level of the Vaaldam is dropping now sharply and water use will also increase from about August when warmer and more windy conditions usually occur. The level of Lesotho dams supplying water to the Vaaldam are also low with Katse dam below 40% and Mohale dam at about 15%. Dams in the Eastern Cape are also at low levels for this time of the year but some rain in the last week of May may improve levels somewhat. Dams in the Western Cape are also at relative low levels but with the rainy season on hand can and must improve.

ENSO and Indian Ocean

ENSO (El Nino Southern Oscillation)

The 2019/20 season is classified as El Nino with a weak El Nino that occurred since about November 2019. Although it was classified as El Nino, were there also neutral type of reactions like the above average rainfall over the central parts of South Africa that is more neutral to La Nina than El Nino. Typical El Nino type of reactions of severe drought occurred over most of Australia and wet conditions over the northern parts of Argentina.

There is currently a rapid change taking place to replace warmer surface water in the Nino areas to cooler than normal surface water. Forecasts currently favour the development of La Nina or neutral conditions. The probability of El Nino redevelopment is currently given as about 10% by NOAA/National Weather Service of the USA. All the Nino areas are now well within the neutral range and forecasts favour a further cooling although there is still some volatility possible. More certainty from about August to September.   

Indian Ocean

The Indian Ocean Dipole (IOD) was in a positive phase (unfavourable for rain) from about July to December 2019. It changed to neutral since then and was probably at least partly responsible for favourable rainfall conditions over large parts of the country since the start of 2020.

Although there is a high measure of volatility of Indian Ocean surface temperatures, are there currently indications of IOD remaining in neutral territory or entering into a negative phase. Four of six models surveyed by the Australian Bureau of Meteorology indicated that negative IOD levels will be reached in July 2020. 

Rainfall and Climate expectations

Summer Rainfall Area

Very little of no rain is expected for most of the Summer Rainfall Area for at least the next two to three months and even for at least the next six months for the western parts of the Summer Rainfall Area. If the IOD (Indian Ocean Dipole) changed rapidly to a strong negative index value it can improve the probabilities for late winter and spring rain. The current outlook for a La Nina event in association with a possible negative IOD (Indian Ocean) can result in a very positive outlook for summer rainfall, especially for the central to western parts but can be drier over the more eastern parts in the second part of summer.

Similar years in history resulted mostly in above average rainfall and even flooding. Years in history with both La Nina and IOD negative present were 1974, 1989 and 2010. All three years recorded well above average rainfall for a place like Vryburg (about double the annual rainfall) while Bethal recorded about average rainfall with a very wet first part of summer and dry second part (February-May). The distribution in Vryburg was a drier first part of summer and very wet in January to April.

Short to medium term can the Eastern Cape (that is between the summer and winter rainfall zones) expect again some significant falls of rain in the second week of June. It is possible that the rainfall may extent into the interior of the eastern Free State and adjacent parts of KZN and Lesotho during this time with possible snow on the Drakensberg range.

Winter Rainfall Area

Current rainfall outlooks are in the range between average and below average for the next three months. Short to medium term outlooks shows however some light rain on a weekly interval for at least the next 3 to 4 weeks.  More significant rainfall is possible in the second week of July. The general outlook is however for below average amounts of rain but is seems that regular light falls are possible.

Namibia

Lower temperatures with frost can be expected in the second week of June. Very little or no rain is on the cards for at least the next four to five months.

Summary and conclusion

• Agricultural conditions improved over large parts of the country since the beginning of 2020. Drought conditions persist over the far western parts of the country as well as parts of the Eastern Cape interior. Significant falls of rain in the Western Cape at the end of May alleviated the severe drought conditions in this area and will allow planting of crops.
• Both ENSO and Indian Ocean (IOD) are most probably heading for favourable rainfall conditions for the summer of 2020/21, especially the central to western parts of the Summer Rainfall Area.
• Rainfall outlooks for the Winter Rainfall Area are less favourable for the next months in terms of total rain but distribution of smaller amounts over regular intervals can assist to improve production conditions.
• Very little or now rain is expected for Namibia for the winter and spring.   

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Contact detail

Email: wjvandenberg1959@gmail.com
Cell: 082 3744692

Source: Johan van den Berg - Independent Agricultural Meteorologist (M.Sc Agric, Agricultural meteorology, UFS)