Namibia’s weather is influenced by the beating of very distant weather drums, as distant as the mid Pacific Ocean along the equator. The drumming speaks of an alternation between the warm current known as El Niño Southern Oscillation (ENSO) and La Niña, the colder opposite. Fishermen, encountering the warm currents at Christmas time along the south American coast, named it after the Christ child, El Niño. The opposite was nicknamed La Niña – the little girl. While neither are necessarily forecasts for rain, Namibian’s love hearing that the little girl might be on her way across the southern African sub-continent.
Often resulting in an intensity of rain absent during a Le Niño event, La Niña speaks of a time of plenty with the desert blooming in grand profusion. The drumming of El Niño on the other hand often tells of the possibility of early rains – as early as August. However, it can also tell of long dry periods between rain events, especially in the peak rainy season when up to 70% of Namibia’s rain should be falling.
Graph below: Mean seasonal cycle of sea surface temperatures in equatorial Pacific Ocean.
Left box: An eastward expansion of warm water (red) indicates an El Niño oscillation.
Looking at the right hand column of the graph, the blue scallops or “cold tongues” of La Niña events coincide with Namibia’s great rainfall years: 2000, 2008/9; 2010/11 (2012 being the strongest on record).
It isn’t necessarily a unanimous agreement on what constitutes these events, and each region has a different relationship with ENSO. While some areas may receive a lower than normal rainfall during an El Niño event, other areas receive high rainfall due to moist air imported from the Indian Ocean. Generally, however El Niño oscillation results in a below average rainfall.
The length of events can vary from a few months to a few years. El Niño tends to last 9 – 12 months while a La Niña event can last up to 3 years, as is evidenced by the 2010 – 2012 event. Since 2012 Namibia has suffered the devastating effects of low rainfall often associated with El Niño years.
Image left - 2011 rain year and our horses looking fat and sleek with the abundance of grass and herbs available
Namibia’s general aridity stems from its location on the rain shadow side of the African continent where rainfall is far less than on the more tropical Eastern side. Added to this, the sub-tropical belt of high pressure encircling the earth tends to shed its moisture further north over equatorial Africa.
Circulating at a great height the moisture sinks into the high pressure cells (anticyclones) centred over the tropics of Capricorn and Cancer. There are layers of dry air far above ground which thirstily absorb the moisture so that the intensity of showers is limited and little actually falls to earth as rain.
The Kuiseb 'badlands' after 4 years of no rain - the Namib is no less beautiful however
In 2012 Namibia experienced the addition of another event known as the Benquela Niño where warm water intrusions in the Atlantic, in tandem with a La Niña event, increased the intensity of the rains. Some areas bordering on the Namib received an unprecedented 1000 mm of rain during that summer – incredible for such an arid area.
During this event several of Namibia’s westward flowing Ephemeral rivers reached the sea – even the Swakop river which, having several dams upriver, seldom flows to the Atlantic.
Image left: The Swakop River - for those who have ridden a Namib Desert Safari - imagine a beach canter with this monster in the way!
While predictions for the 2016 summer seem to indicate another Le Niño oscillation, Namibian’s always live in hope that the weather-man might be wrong...
The group Toto were right to “bless the rains down in Africa” in their song entitled “Africa” – there are few sensual pleasures quite so exhilarating as the sensation of copious rain on hot, parched earth. It is something everyone should experience at least once in a lifetime.