Day Zero in 2019 determined by April’s rainfall

In three weeks’ time experts will be able to say with some certainty whether Cape Town is likely to get enough rain this year to avoid a Day Zero scenario in 2019.

After three dry years and months of severe water restrictions, everyone in the drought-stricken area wants to know whether we will get the above-average rains we need to fill the dams sufficiently to break the drought and see us through next summer.

Now scientists Peter Johnston and Piotr Wolski at UCT’s Climate System Analysis Group have worked out that April is key to answering that question.

After analysing rainfall figures from the Western Cape dam catchment areas from 1930 to 2017, they found that if rainfall recorded by the end of April is above normal, it is likely that we will have above normal rainfall for the rest of the year.

“If the cumulative total is above normal by the end of April we can say there is a 70% chance of it being wetter than normal by the end of the year,” Johnston said.

If the rainfall by the end of April is average or below average, it does not throw light on the rest of the year’s rainfall – but May and July have some answers in that regard.

The researchers have found that if by the end of May we have had below average rainfall, we are likely to have below average rainfall for the rest of the year.

“And if rainfall by the end of May is normal, there is an equal chance of going either way.”

If rainfall figures at the end of July are normal, it is likely we will have normal rainfall for the rest of the year.

“So based on statistics, if it is wetter than normal at the end of April, we are likely to have a wetter than normal year; if rainfall is normal at the end of July, we are likely to have normal rainfall and if it is drier than average at the end of May, we are likely to have a drier than average year,” Johnston said.

Might take time

Nicky Allsopp, manager of the Fynbos Node at the SA Environmental Observation Network (SAEON), said dam levels might take some time to recover.

Because of three years of drought, soils had dried out and would act like sponges, absorbing a lot of rainwater and reducing run-off into dams.

She said rainfall measured at Jonkershoek, in the same mountains as the Berg and Theewaterskloof dams, showed that the last three years had had the lowest rainfall since records began in 1961.

“It has not been as dry as the 2015 to 2017 period in the 56-year record,” she said.

The drop in stream flow since 2014 was unprecedented.

Allsopp said we would have enough water to fill the Cape dams sufficiently to supply water into next year only if there was a higher than normal rainfall during the rest of the year.

“It looks like we would need at least four consecutive wetter than normal months in the catchment to get enough runoff into the dams. Every time it rains more than 20mm, we are likely to get some surface flow because the soils can’t absorb it all. But rainfall of 10mm or less will just wet the soil,” she said.

However, five consecutive days of 10mm of rain would result in stream flow into the dams. — News 24

These are unprecedented times, and the role of media to tell and record the story of South Africa as it develops is more important than ever. But it comes at a cost. Advertisers are cancelling campaigns, and our live events have come to an abrupt halt. Our income has been slashed.

The Mail & Guardian is a proud news publisher with roots stretching back 35 years. We’ve survived thanks to the support of our readers, we will need you to help us get through this.

To help us ensure another 35 future years of fiercely independent journalism, please subscribe.

Advertisting

Odd drop in how Covid-19 numbers grow

As the country hunkers down for a second week of lockdown, how reliable is the data available and will it enable a sound decision for whether South Africans can leave their homes on April 16?

Mail & Guardian needs your help

Our job is to help give you the information we all need to participate in building this country, while holding those in power to account. But now the power to help us keep doing that is in your hands

Press Releases

New energy mix on the cards

REI4P already has and will continue to yield thousands of employment opportunities

The online value of executive education in a Covid-19 world

Executive education courses further develop the skills of leaders in the workplace

Sisa Ntshona urges everyone to stay home, and consider travelling later

Sisa Ntshona has urged everyone to limit their movements in line with government’s request

SAB Zenzele’s special AGM postponed until further notice

An arrangement has been announced for shareholders and retailers to receive a 77.5% cash payout

20th Edition of the National Teaching Awards

Teachers are seldom recognised but they are indispensable to the country's education system

Awards affirm the vital work that teachers do

Government is committed to empowering South Africa’s teachers with skills, knowledge and techniques for a changing world

SAB Zenzele special AGM rescheduled to March 25 2020

New voting arrangements are being made to safeguard the health of shareholders