Gazing into the Crystal Ball – South Africa’s Future Challenges to Water Quality

29 June 2012

Anthony Turton

This is an invited viewpoint by Dr Tony Turton of the Water Stewardship Foundation Trust.  The article contextualizes many of the points made in this blog regarding the issue of water quality in relation to the Water Crisis:

I often get asked what the big deal is about water scarcity and quality in South Africa. This opinion piece captures what I consider to be the crux of the matter, presented in the language that a layperson can relate to.

To understand the relevance of water we need to first grasp some fundamental realities. The most fundamental of these is the hydrological cycle that dictates how water flows in time and space as a perpetual cycle. Three elements of this cycle are of critical importance to our understanding of the role of water in South Africa – precipitation, evapotranspiration and runoff – because it is the interplay between these three elements that makes us extremely vulnerable. Precipitation refers to water falling from sky as rain, snow or frost, after condensation has occurred to change its form from vapour into liquid. Evapotranspiration refers to water that is changed in form from liquid to vapour, either as a direct result of evaporation off any open wet surface, or as an indirect result of transpiration from the leaves of plants and trees. Runoff refers to that fraction of water that remains in liquid form after both precipitation and evapotranspiration has occurred, and can be thought of as water in our rivers and dams. It is the latter that forms the hydrological foundation of our entire national economy, so let us home in on some fundamental numbers.

The first fundamental number is the ratio between precipitation and runoff. In the context of South Africa, the two largest river basins are the Orange and Limpopo, sustaining the majority of our national economic activity, so let us focus on these two systems only for illustrative purposes. The conversion of mean annual precipitation (MAP) to mean annual runoff (MAR) in both these systems is a paltry 5.1%. Stated differently, of 100 units of water falling as rainfall, only 5 units end up in the river. The rest – a whopping 95 units – is lost as evapotranspiration. This is a big number because it happens in perpetuity and we actually have little control over it.

So let us get back to our two river basins and home in a bit more on the Orange, which is our most important from a national economic development perspective, because it sustains amongst other things the heartland of the economy in Gauteng, and a major component of our manufacturing at Port Elizabeth. In the Orange, the MAP:MAR conversion in the South African component is a meagre 3.4%. If we call this 3.4% of precipitation that becomes runoff 100% of the streamflow in that system, then we are surprised to find that we have built dams large enough to capture a massive 271.3% of the flow of the river. Stated simplistically, we have almost built three times as much storage capacity in dams as we have water flowing in the river on an annual average. So we have some control over the small number (runoff), but we have little or no control over the very big number (water being lost as evapotranspiration).

This is the heart of our vulnerability problem, because we can build a few additional dams, but those we already have are fast becoming unfit for purpose because of three fundamental processes that are occurring. Firstly, the dams are silting up and we are losing our storage capacity. The Welbedaght Dam, for example, that supplies the Orange Free State economy, had an original design capacity of 116 million cubic metres (mcm) when it was commissioned in 1970. Today it has a paltry 4 mcm of live storage capacity left, effectively reverting back to a free flowing river, the result of siltation. Secondly, the dams we have are fast becoming eutrophic, the result of a complex interplay between agriculture, industrialization and more importantly, failing sewage treatment plant. Today around one third of the total annual storage cycle is eutrophic, with some estimates suggesting that this might approach two-thirds in the not too distant future. Thirdly, climate change is likely to increase the ambient air temperature over large parts of South Africa, with some climate change specialists predicting that we could even see a rise of 4°C in some of the river basins over the next century. This means that the evapotranspiration rates, already very high, will increase, as will salinization. The result of this will probably be a decrease in streamflow now more saline, but more significantly, an increase in primary production, which in the context of eutrophic systems, will potentially result in hyper-eutrophication.

So what is the big deal?

In my opinion there are two big deals we need to know more about.

The first is related to water as a foundation to our national economy. Our total national water resource at a high assurance of supply – the percentage of our national MAR stored in dams and thus available for social and economic activities – is around 38 billion cubic metres (BCM) per annum. We cannot build too many more dams because we are reaching the finite limit of most of our major systems. If we want to have full employment by 2035 we will need about 65 BCM, which we simply do not have. One solution is to transition to a recycling economy and manage water as the flux it really is, rather than the stock we are currently measuring. If we recycle our total national resource available at a high assurance of supply (38 BCM) 1.7 times by 2035, we will effectively have created the 65 BCM we need (38 BCM X 1.7 = 64.5 BCM). This is doable, but it will place major pressure on the aquatic ecosystems, which takes us to our next big deal.

The second big deal is the loss of our scientific capacity, most notably in the field of limnology. For many reasons too complex to summarise here, South Africa has simply lost most of its technical capacity in the field of aquatic sciences. Nowhere has that loss been more dramatic than in the field of reservoir limnology, in which we have seen an almost total collapse. Limnology deals with the range of scientific disciplines that relate to aquatic ecosystems, most notably those occurring in lakes and dams, often with major ramifications for water quality management. A distinct subset of this is the scientific discipline that relates to plankton known as Diatomology, which has almost become extinct in South Africa, despite the best efforts of a small group of dedicated specialists.

Does it make sense therefore, if we are so precariously balanced in terms of the water we have at a high assurance of supply, to allow ourselves to lose the core scientific skills and capabilities we need to manage the very systems on which we are going to become increasingly dependent on?

In my professional opinion, unless we deal with our loss of scientific and technical capacity as a matter of national strategic priority, then South Africa will increasingly become vulnerable to the ravages of deteriorating water quality and loss of assurance of supply on which our national economic wellbeing is totally dependent. Unless we wake up and smell the proverbial roses, we will discover with a shock that our national economy is a wholly owned subsidiary of our national hydrology, and like a credit card that has been maxed out, we will suddenly discover what a limit actually means when enforced by an overly zealous bank manager.

This is what the Water Stewardship Council of Southern Africa is all about – encouraging behavioural change – by educating the entire value chain from resource to sink and back again.

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