Southern Africa Drought, Dam Levels, Outlook June 2017

With this being the dry season over most of Southern Africa the only part that warrants attention as far as rain and dam levels is concerned is probably the Western Cape that relies on winter rainfall. My 6 May post showed that all other provinces (plus Lesotho) had dam levels above 50% of capacity but with the expectation that these, in general, will decrease over winter.

With the first major winter storm having hit the Western Cape a couple of weeks ago (and ironically causing some serious damage and flooding) it is to be hoped that dam levels will now increase steadily for the next three or four months. The main dam, Theewaterskloof (479 million m3 capacity) increased from 13.3% of capacity (close to the minimum at which water can be extracted) on 5 June to 17.2% on 19 June (in the previous post this was given as 18% on 24 April). The comparable figures for the Western Cape as a whole are 17.7% and 21.3% (21%). Some recovery is therefore evident but from extremely low levels. Other quite significant dams are lower than Theewaterskloof: Brandvlei 286 million m3 capacity 14.4%; Clanwilliam 123 m m3 13.3% (from only 8.4% on 12 June); and Kwaggaskloof 170m m3 12.4%.

The situation is serious enough for Level 4 water restrictions in the built-up area around Cape Town. These are quite severe – no watering of gardens with potable water (and with grey water strongly discouraged outside four specified hours per week); maximum daily usage of municipal water 100 litres (equivalent to 10 toilet flushes); the covering of public swimming pools ‘strongly encouraged’; golf courses, schools etc not allowed to establish any new sports fields or ‘landscaping’ except as can be irrigated with non-potable water.

The area is said to be experiencing its worst water shortage for 113 years. A disaster area has been declared in terms of which R3 billion will be diverted to projects to mitigate the effects.  Water and Sanitation Minister Nomvula Mokonyane has said: “We have identified the Table Mountain group aquifer, the Berg-River Voelvlei Dam augmentation scheme and exploration of new technologies, such as desalination, water re-use and rainwater harvesting, to assist us in building a water-secure future for the province and to mitigate the effects of drought.” This is all very well but one does not get the impression that any significant action has been taken over recent years to accommodate the water demands of an expanding population in an area where there is limited potential for additional significant capacity dams. I find it difficult to be optimistic about the situation for the short and medium term.

The following graph shows how the 2016/17 rainfall has been well below average, except for January, for the Western Cape as a whole. In combination with dam levels this indicates that some exceptional rainfall will be needed to avert a continuing crisis.

W Cape rain 2017

This is in contrast to the 2016/17 season (in this case July to June) rainfall in my own part of Gauteng province which has reached 1069mm, a roughly once every eight years occurrence for such a high rainfall. Even May, frequently dry, achieved 58mm. More typically the last five weeks have not seen any rain. Less typical has been yet another mild winter to date. Whereas a few years ago we would have expected average daily minima in June below 1°C (2011 0.1 and 2012 0.3°C), June 2017 to date (23rd) has only seen one day below 2°C and all but three days reach 20°C.

Despite the decline of El Niño, referred to in my 7 May blog, the prospects of a La Niña, with an increased likelihood of rain, are not that good. By way of a variation on the chart I presented in the last blog on this topic I include a plume of the predictions of various institutions around the world for the El Niño Southern Oscillation compiled by the International Research Institute for Climate and Society of Columbia University’s Earth Institute. It will be seen that these predominantly forecast a continuation of the current positive sea surface temperature (SST) anomaly in the tropical Pacific and therefore a tendency to an El Niño rather than La Niña event. The notable exception to this is the Scripps Institution of Oceanography of the University of California, San Diego, which uses what they call a Hybrid Coupled Model, combining a “big, comprehensive general circulation ocean model coupled to a much simpler, statistical atmospheric model.” It’s interesting that unlike all the other forecasts this one predicts a negative trend in the SST from the current observed level right through to at least early 2018 and with an increasing gradient. Even so many of the forecasts are within the 0.0±0.5°C neutral band. The prediction for the highest positive anomaly is from Saudi Arabia’s King Abdulaziz University.

IRI£1

Sources: www.capetownpartnership.co.za      http://iri.columbia.edu   http://www.dwa.gov.za

 

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