Drought every 10 years: Cape water woes far from over

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Drought every 10 years: Cape water woes far from over

The current water shortage is characteristic of longer-term weather patterns, scientists warn

Cape Town bureau chief

The Western Cape could face a drought every 10 years, say European Commission experts.
Scientists from the organisation’s Joint Research Centre, who analysed data from its Global Drought Observatory, looked at rainfall in Southern Africa over the past 36 years and found a strong probability of a 50% to 70% monthly deficit every five years.
This means more moisture is lost through evaporation and transpiration than is gained through rainfall.
In the Western Cape, though, the deficit could be as high as 70% to 80% every 10 years, they said.
A new technical report from the Joint Research Centre says the current water shortage – due to low rainfall for three successive winters – while exceptional, is characteristic of longer-term weather patterns.
With climate change spurring more extreme weather events, severe shortages could become increasingly regular in the future, they say.
The scientists also analysed the frequency of warm-weather events, and found an increasing number of moderate to extreme heatwaves in Southern Africa over the past decade.Combined with an expected growth in Cape Town’s population of 5% over the next five years, they warned that these factors made more frequent water crises likely.
However, they said the ability to predict periods of drought would help policymakers to make contingency plans, including diversification of food production towards more drought-resistant crop varieties.
The predictions would also permit more informed decisions about whether development projects should be allowed in such a risky area.
The European report comes as May rainfall – while remaining well below long-term averages – begins to flow into Cape Town’s dams and revive water courses such as the Breede River.At 24% full as of Monday, the six major dams are 2.9 percentage points fuller than a week earlier, and more than four percentage points above their level of 19.8% a year ago.
More than 30mm of rain is forecast for the catchment area of Theewaterskloof, the biggest dam, on Friday and Saturday.
This will boost the dam’s level beyond Monday’s 14.9%, but scientists warned this week that alien plants absorb more than 100 million litres of water a day that would otherwise reach Theewaterskloof and other dams.
Writing in GroundUp, Jasper Slingsby and Mark Botha said these losses were expected to triple by 2050 if they were not addressed. However, clearing the aliens could provide employment for some of the 30,000 farmworkers who had lost their jobs because of the drought.
“Not only our dams, but also our aquifers, and therefore the [City of Cape Town’s] plans to extract water from them, are suffering from reduced recharge due to alien trees in our mountain catchments,” said Slingsby, of the South African Environmental Observation Network, and Botha, an independent researcher.
“Becoming dependent on groundwater without addressing the greatest threat to the resource, is lighting the fuse on a time bomb.”
The scientists want Cape Town, which has budgeted R1.5-billion to augment its water supply, to spend R120-million a year for up to a decade on eradicating invasive aliens in catchment areas, saying it could add 50 million litres a day to the city’s water supply.

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