Heavy rains over the last few days swelled Cape Town‘s dams to 26.1% of storage capacity by Friday afternoon – but the region is still a long way away from the 85% the authorities require before water restrictions can be lifted.
While some residents in the flooded Cape Town suburbs of Goodwood and Parow were wading through ankle-deep water in their homes on Friday, it may have seemed ironic that they were nevertheless subject to severe water restrictions that allowed them to use no more than 50 litres per person a day.
Rashid Khan, regional head of the Department of Water Affairs and Sanitation, said while the cold front had brought good rainfall in the mountains that formed the catchment areas for Cape Town‘s dams, total water storage was still low.
“We‘ve had lovely rains, some good rain at Theewaterskloof and Wemmershoek, but this is still early in the rainy season, so we can‘t say how the rest of the winter will be,” he said.
The decision was made by the department that the City of Cape Town‘s dams had to be 85% full before restrictions on the City, including its agricultural sector, could be lifted, he said.
“We‘ll all meet in late September, early October to see what the total winter rainfall has been like, and we‘ll make decisions then,” Khan said.
Unreliable long-term predictions
The cold front that brought rain and gale-force winds increased Cape Town‘s dam levels from 24% on Monday to 26.1% on Friday.
This week in 2017 dams were 19.8% full.
The question everyone wants answered is how much rainfall can be expected for the rest of the winter – and it appears there is no reliable answer.
Cobus Olivier of the South African Weather Service said this was because unlike the summer rainfall region, there were difficulties in modelling the systems that brought winter rainfall to the country.
“So confidence levels of long-term predictions for South Africa‘s winter rainfall area are low,” Olivier said.
He said the analysis for last month indicated that early winter rainfall was likely, and that June, July and August rains may be above average – but the confidence levels of this being accurate were low.
Varying rainfall patterns
In the Jonkershoek mountains the total rainfall for May was 353mm, while the long-term average for May at this station was 391mm.
Nicky Allsopp, manager of the fynbos node at the South African Environmental Observation Network said this was measured in the same mountains that formed part of the catchment area for Cape Town‘s dams.
“So it rained where it matters, which is good. It is still early days, but the frontal systems seem to have reverted to bringing a few days‘ rain in a row. The dams are filling because if you get a lot of rain in a short space of time, there is quite a lot of run-off overland,” Allsopp said.
She said some researchers had suggested that if the winter rains started earlier in the year, it was more likely that the winter rainfall would be normal.
The rainfall had been very varied in the province during May, with some areas getting a lot and others very little.
Some rainfall figures for the 24 hours up to 08:00 on Friday were 23.8mm for Cape Town city, 72.4mm for Kirstenbosch, 19mm for Morreesburg, 50.8mm for Villiersdorop, 19mm for Saldanha and 7.6mm for Bredasdorp. There was no rain recorded in Beaufort West and surrounding areas.
Capetonians warned against complacency
“We‘re still in a drought. In some places around the world when there is a drought there is no rain at all, so psychologically people know there is a drought, but in Cape Town it is different. You go outside and you get wet. This drought is very different from the type of drought people envisage like the dust bowl of the United States,” she said.
Allsopp said although there had been three very dry winters in a row from 2015, the water crisis had not come sooner because of the “cushion” effect of the water stored in dams, aquifers and cracks in rocks.
“The system can hold a lot of water, so it was only last summer that the dams got dangerously empty.”
Allsopp said although the recent rains were promising, Capetonians should not become complacent.
“We cannot assume that the climate is returning to whatever normality is.”