Climate outlook for 2020

Climate outlook for 2020

The variable and changing climate

Climate conditions were in general unfavourable for agricultural production in the recent past seasons. Severe drought over most of South Africa and especially the central, western, south western and south eastern parts of the country already persists since about 2012. In areas where higher rainfall amounts occurred was the distribution over time unfavourable. For example, in the Western Cape where very little rain occurred in the crucial growing months for winter crops of August and September with lots of rain after that during the harvesting process. Very cold conditions with frost occurred towards the end of October 2019 that caused severe damage to the winter crop in the Free State and Northern Cape. Crops like grapes, nuts and early planted summer crops also suffered damage. Severe hail damage occurred in the second part of the 2018/19 summer season and crops like avocados, citrus, nuts and other fruit suffered severe damage. The maize crop also suffered damage and total losses occurred in places that is unusual for maize.

What are the reasons for this highly variable climate?

There are different factors that can be responsible for deviations from the long term average conditions.

Natural cycles

Firstly, is there a natural cycle of consecutive seasons of below average rainfall and on the other hand consecutive years or seasons with above average rainfall. Large parts of the country, Namibia and Botswana currently suffering from below average rainfall since about 2012. There were however similar periods with below average or drought years in the past like between 1964-1970, 1982-1987, 1992-1998 and 2003-2007. Severe drought periods also occurred between 1926-1933 and 1945-1953. This is also not unfamiliar on a global scale and was there a period of about 16 consecutive years with below average rainfall from about 1900 to 1916. Another drought spell occurred between about 1940 and 1947, between 1980 and 1987 and from 1990 to 1997. Extremely wet spells occurred globally from 1952 to 1963, 1974 to 1976, and 2002 to 2010. There are also longer term trends with the first about 5 decades between 1900 and 1950 with a much higher frequency of dry years compared to the period since then.

ENSO (El Nino Southern Oscillation) and Indian Ocean

Oceans are very important in generating or changing climate systems due to the variable energy levels exposed to the atmosphere. Changes in ocean surface temperatures can cause large scale differences in climate systems. The El Nino-phenomenon that is part of ENSO, can disrupt weather systems by spatially “shifting” rainfall and temperature patterns within hemispheres but also across hemispheres. El Nino is usually responsible for below average rainfall over most of southern Africa, especially the central to western parts as well as the central to eastern parts of Australia, northern parts of South America and most of North Africa. Above average rainfall is often characteristic of El Nino events in Argentina and surroundings, East Africa (Tanzania, Kenia, Uganda), southern parts of North America and parts of China and India. La Nina events usually cause above average rainfall and often flooding in Southern Africa, especially the central to western parts of South Africa, Namibia, Botswana and even parts of Zimbabwe; eastern parts of Australia; northern parts of Brazil; Canada and northern parts of Asia.

The Indian Ocean is also responsible for disrupting “normal” climate patterns. Warmer than average water towards the African coastline and corresponding cooler water towards northern Australia and Indonesia can redirect the normal south and south eastward flow of moisture from the tropics towards the Indian Ocean. This results in heavy rainfall over the western Indian Ocean and adjacent east African countries like Tanzania, Kenia and Uganda. Drier conditions then occurred over southern Africa and most of Australia.

A “super” system usually come into play over Southern Africa and Australia when there is an El Nino as well as warmer western Indian Ocean waters simultaneously like in 2015/16. This can be responsible for a super drought with both factors contributing towards weaker rainfall conditions.
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