What about the day after Day Zero?

Panicked Capetonians are asking the wrong question. The issue is not when Day Zero will see their taps turned off. That won’t happen this winter. They should be asking: What will happen next summer?

We know that it will rain over the Western Cape over the next few months. What we don’t know is where, when and how much rain will fall.

When Day Zero was still set to be reached on April 12, Accuweather forecast that the city’s first big rains of the season would start on … April  12. With remarkable precision, they predicted that 19mm would fall on that day, with 13mm and 10mm on following days. That internet forecast is almost certainly wrong. Indeed, two weeks later, it had been completely changed — at the time of writing, only 5mm is forecast for the whole of April.

Even the best weather services are pleased if their five-day forecasts are reasonably accurate. Climatological science suggests that 15 days may be the outer limit of what may be achieved in the future. Forecasts for longer periods are simply guesswork and are deeply misleading and distract people from the real issue: we have to live with weather that is not predictable.

So what can we say about the day after Day Zero? And what will that mean for the people of Cape Town?

The starting point is to admit that we don’t know — the future is just too uncertain. All that technicians like me can do is offer a range of scenarios — good, bad and average. And we can suggest how to cope with each.

The best case would see the Cape Peninsula enjoy good early rains that continue right through winter. In an exceptional year, this might even fill dams to their “normal” levels. That’s what happened in Gauteng last year when the tail end of Cyclone Dineo refilled the Vaal systems’ dams in just a few days.

The worst case will see the drought continue. If the coming winter rainy season is as dry as the last one, dam levels will go up but not by very much. They will start the 2018 summer significantly lower than they were in 2017.

Even if there are good rains, Cape Town will probably have to continue to restrict supplies. The city needs more water than its existing dams can supply. Current emergency efforts to get more water from boreholes and water reuse (and a few small and very expensive temporary desalination plants) are unlikely to provide enough.

The technicians currently estimate that, at best, they will have an extra 150 megalitres a day of new supply when summer starts. They need 250 megalitres a day before they can be comfortable, even if the dams are back to normal. Before the crisis, Cape Town’s daily consumption was reaching 1 200 megalitres a day.

So, even in the best case, citizens are likely to spend the summer of 2018-2019 with water restrictions but perhaps not as acute as at present.

In the worst case — another dry winter — the city will remain on the brink of disaster. Together with a trickle from the dams, the new sources will only maintain supply at existing levels, less than half the pre-drought normal. Drastic restrictions will have to be maintained, agriculture will be cut back further, jobs will be lost and the tourist industry will have another disastrous season. It could still reach the point where people have to queue in the streets.

Only by the summer of 2019-2020 is the city likely to have an efficient, permanent desalination plant running. This could provide an additional 100 or 150 megalitres a day. Together with the expected supplies from groundwater and water reuse, this will allow the city to scrape through if it suffers another serious drought, although, even then, restrictions will still probably have to be imposed while dam levels are restored.

At that point, if the experience of Australia and Spain is anything to go by, there will be a decade of good rains. Nature has a cruel sense of humour. When those countries invested billions in desalination to deal with drought emergencies, the desalination plants were hardly used in the following years.

What Water Affairs and Sanitation Minister Nomvula Mokonyane calls the “new normal” is hardly novel. Cape Town is continuing a long history of procrastination followed by unpleasant climate surprises. A century ago, when the city’s Table Mountain springs no longer provided enough to meet citizens’ needs, the local village councils dithered about what to do next. A drought emergency finally persuaded them to co-operate to build the Steenbras Dam. “Will it come to this?” asked cartoons at the time, picturing queues of Capetonians with buckets.

The rest of the country should learn from Cape Town to be prepared. Don’t take chances with your water supplies. If Cape Town had taken the guidance of the National Development Plan, which recommended in 2012 that it should develop groundwater supplies and wastewater reuse by 2017, there would be less drama today. Although Western Cape Premier Helen Zille says the cost of such early investment would have been excessive, it would have been a very cheap insurance policy given the scale of losses that they are currently suffering.

So learn from their mistakes; don’t repeat them. Use your water wisely but keep paying those insurance premiums — invest in the right infrastructure, at the right time.

Mike Muller is a visiting adjunct professor at the Wits School of Governance. A professional engineer, he was also director general of the water affairs department from 1997 to 2005 and a member of the National Planning Commission from 2010 to 2015