Southern Africa Drought #2

There has been speculation that the El Niño phenomenon, believed to have caused the drought in Southern Africa, would be succeeded by a significant La Niña phenomenon, which generally indicates a wetter spell. However the following graph from the International Research Institute (IRI) at Columbia University’s Earth Institute in New York reproduced below is less than comforting in that respect. It shows the climatological probability of an La Niña at  less than 35% and even then only until about January whereafter it declines to around 20%. During the first half of next year the forecast is heavily biased towards a neutral situation where sea surface temperatures (SST) in the relevant Pacific area (area 3.4 in this instance) are within 0.5°C of normal (the SST anomaly). IRI believes the trade winds in the relevant areas being no stronger than normal will prevent a sustained La Niña phenomenon and they point out that the La Niña watch put out by the National Oceanic and Atmospheric Administration’s Climate Prediction Center in June has been cancelled. IRI’s forecast is thus rather for a weak La Niña, at best, with correspondingly weak effects. When it comes to specific parts of the world IRI does not predict above normal rainfall for the summer rainfall area of Southern Africa.

iri-enso-sep-2016

The chances of the drought being decisively broken in Southern Africa thus does not seem particularly good. In the five weeks since I last reported on dam levels there has been a rise of 1% or so in Western Cape dam levels thanks to some further winter rain over the province but despite what seem to have been good rain in some coastal areas, especially in kwaZulu Natal, all other areas report declining levels. Drops of around 10% of their late August levels are recorded for the Vaal, Bloemhof, Vanderkloof, Lesotho and Mpumalanga dams which together represent some 30% of RSA/Lesotho capacity. With Vaaldam and the Lesotho dams now  below 35% of capacity the only favourable aspect is Sterkfontein which has been maintained at 90%. I have seen no indication of when water might be released to Vaaldam from there.

Compared to early October last year (ie eliminating seasonality) dams in Mpumalanga, Limpopo and Lesotho are more than a third down, Free State and kZN a quarter or more and W Cape about one eighth (part of the reason for the last one being that that the baseline is the end, rather than the beginning, of the rainy season).

My own part of the Highveld summer rain area has not yet received any good summer rains. Despite some unusual winter rain only 39mm have been recorded since the beginning of June representing a negligible contribution to water supplies. In recent weeks this has been exacerbated by high temperatures and very low relative humidity accompanied by stronger than normal winds (with a corresponding increase in veld fires).

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