Why is there so little water in the Western Cape?
There are two distinct pressures on the Cape's water supply. The first contributor is a weather phenomenon that climatologists call ENSO, or the El Nino Southern Oscillation. In short, tiny wobbles in ocean currents, sunlight levels, and a few other things over the Pacific Ocean can cause big wobbles in global temperatures and rainfall patterns. Some parts of the world can get wetter, which sounds nice until you realise that they're as unprepared as we are, and wetter typically means flooded.
The southern end of Africa is one of the parts that gets drier. The eastern side of this southern end of Africa (think Mozambique, Zimbabwe, Botswana, Swaziland, and Madagascar) usually gets it worse than we do. The South African Weather Service has a great explanation of ENSO on their website. They also have a media release detailing the precarious and sensitive situation we're currently in.
While you might think that these patterns should be possible to forecast better, it seems that that is not the case - as it so often is with the weather. Long-range forecasting by local and international climatologists failed to adequately predict the severity, and even the occurrence, of the conditions we are currently facing. If they missed it, then you can be sure civic planners and politicians were in the dark, too.
The second contributor is the growing population of the Western Cape. There are by now about 6.8 million people living in the province, and this number grows at around 2.3% per year. Cape Town alone currently encompasses 4.5 million of those people, and this number is increasing at an even greater rate, around 2.6%. Statistics show that those living in informal settlements, on average, consume around 40 litres per day - still under the latest water restriction level! - and that cumulatively, informal settlements use less than a twentieth of the water consumed within the metropolitan area. This makes it clear that national immigration patterns are not to blame, but rather, a growth in households and household water consumption in formal areas has contributed to the population effect on water resources.
In 2009, the Berg River Dam was inaugurated, which contributes 130000 megalitres of capacity to the local water supply network, or 17% of present capacity. Currently, work is underway to raise the Clanwilliam Dam wall by 13 metres for a further 70000 megalitres of capacity. While growth in supply has not been stagnant - despite political inferences that suggest otherwise - the impact of decreased rainfall coupled with the continued high population growth means that drought conditions were probably inevitable.