Southern Africa Climate, Outlook and Dam Levels Update May 2017

The northern part of the region has moved into its dry season with a fairly sharp cutoff in our Gauteng province but with Free State dam levels looking good after above average summer rains. In the water short southern parts rains have not set in sufficiently to impact significantly on dam levels.

Columbia University’s International Research Institute for Climate and Society’s mid April El Niño Southern Oscillation (ENSO) forecast reports the tropical Pacific as being in an ENSO-neutral state, with above-average sea surface temperatures (SSTs) present in the eastern Pacific Ocean, and near-average SSTs across the central and east-central part of the basin. Their model predictions, adjusted for human forecasters’ judgement and experience, is for a return of El Niño conditions as the year progresses as shown in the graph below.  While this looks heavily skewed in favour of a return of El Niño the unadjusted model based forecast has the El Niño probability reaching as high as 70% in the third quarter.

ENSO May 2017

We are now in a spell when the rains have more or less come to a halt at the end of the northern parts wet season, with good rains still to arrive in the southern winter rainfall area. In our own area of Gauteng province April was, to us a soccer term, a month of two halves with a distinct change from mainly warm days with good rains to cooler dry weather in the second half, as the following table indicates. Larger daily temperature ranges are a feature of the dryer weather.

April 2017

Average

Average

 

minimum maximum

Rainfall

 

°C

°C mm

April 1-15

12.7 24.3

83

            16-30 7.4 22,0

2

This rain brought the total for the season (July to June) to date to over 1,000mm, a figure which is exceeded only about once every five years. The heavy rains of January and February over some areas induced some complacency about the state of water resources but in reality did not bring complete relief to many areas. In my last blog on this topic I showed the very rapid increase in dam levels to 20 March but the table below shows there has been no follow through, with no provincial increases except for Mpumalanga. The drop is most concerning in the Western Cape where the major dam supplying Cape Town is fast approaching the minimum level at which water can be extracted. The Water Affairs website was down at the time of writing but the Cape Town situation has continued to worsen post 24 April.

 Capacity  24.4.17  20.3.17
              Dam million m3 % %
Sterkfontein        2 617            90            89
Vaal        2 604           103           106
Bloemhof        1 240           101           105
Vanderkloof        3 171            64            59
Gariep        5 196            93            97
Free State total       15 971            86            87
Theewaterskloof           479            18            23
W Cape total        1 853            21            27
Pongolapoort        2 267            41            41
kZN total        4 669            53            55
E Cape total        1 826            62            63
Limpopo total        1 508            79            79
Katse / Mohale (Lesotho)        2 376            54            56
Mpumalanga total        2 520            79            78
Total RSA and Lesotho       31 913            73            74

 

 

 

 

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