May mayday! UCT boffins home in on month that points to more droughts
Extreme droughts are going to become more common, and climate change is making things worse, say scientists
It’s not the news Cape Town wanted in the week when collective daily water consumption exceeded 600 million litres for the first time in a year.
“Very severe droughts like 2015-17 can be expected to occur more often in the Cape Town region in the future,” said scientists at the universities of Cape Town and Lisbon.
The geoscientists and oceanographers who published their conclusions in the journal Environmental Research Letters said the drought was caused by “poleward migration of moisture corridors” that normally deliver the Western Cape’s winter rainfall.
Climate change was expected to accelerate this movement, said UCT oceanographers Ross Blamey and Chris Reason.
Their study, which was completed last October, said Cape Town “should manage” until 2019’s winter rainfall arrives, “so long as consumption remains at not much more than 70 litres per person per day”.
A relaxation in water restrictions from December increased the individual daily consumption limit from 70 litres to 105 litres, and last week the City of Cape Town got through 604 million litres per day, against a target of 650 million.
Blamey and Reason said severe consumption curbs were not sustainable in the long term. “The need to effectively ‘crisis-manage’ water usage is detrimental to human welfare, ecosystems health and the regional economy,” they said.
“Unfortunately, most studies have found evidence of Mediterranean climates, such as the Cape Town region, being more susceptible to impacts of climate change.
“The shortening of the winter rainy season has also been pointed to as a key factor for the expected drying trends in these climates.”
During Cape Town’s drought years of 2015-17 – also the warmest three years on record in terms of global average surface temperature – the scientists said, “near-normal rainfall has been restricted to mid-winter months”.
May, in particular, was a problem. While it was normally the fourth-wettest month of the year, between 2015 and 2017 it produced only about a third of its normal rainfall.
Blamey and Reason warned that the likelihood of an extreme drought such as the one that almost brought Cape Town to Day Zero, when taps would have been turned off, “has increased by about a factor of three at the present rate of atmospheric warming associated to anthropogenic causes”.
The study comes as the dam levels in the Western Cape slip below 50% and the Karoo remains in the grip of drought.
Anton Bredell, the MEC for local government, environmental affairs and development planning, said seven water tankers had been sent to Zoar, between Ladismith and Calitzdorp, where reservoirs ran dry at the weekend.
“The Zoar region currently uses 170 litres of water per person per day. The community has been urged to reduce consumption to 50 litres per person per day,” he said.
“Work in Laingsburg and Beaufort West is also continuing. The department has several experts on a fulltime basis in the area to address concerns.”
Reservoirs in Zoar were being replenished by groundwater, said Bredell. “We must again repeat that there is a serious water challenge in the Karoo, but to date no community has run out of water and many areas are still getting water from groundwater sources.”
• Northern Africa has seen a threefold increase in mega-storms over the past 35 years, a five-year study by the UK government has found.
The so-called mesoscale convective systems, which can be as high as 16km and destroy everything in their path, are increasing in number on the Sahel due to climate change.
Chris Taylor, meteorologist at the Centre for Ecology and Hydrology in the UK, said the storms were caused by the temperature difference between the Sahara to the north and tropical forests to the south.
“These vigorous storms have always happened, but they’re becoming more common and are getting stronger,” he told the Daily Telegraph.