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February 16th, 2015
Via South Africa’s Business Day, an interesting look at the rise of megacities and the resulting impact on water stress:
MOST of the megacities housing more than 10-million people that will spring up around the world in the next 100 years will be in Africa, which makes it critical to plan now for their sustainability in water consumption, Water Research Commission (WRC) CEO Dhesigen Naidoo said last week Wednesday.
In the past 15 years, SA had experienced rapid growth in two cities, Mbombela and Rustenburg, and the opportunity to plan them with water sustainability in mind had been lost, he said.
He was speaking at the WRC’s launch of the Water Sensitive Urban Design Framework, which sets out how SA should be planning the water infrastructure of its future cities.
According to the 2011 Census, 63% of SA’s population lives in urban centres and this is expected to reach 80% by 2050.
This means water security has to be a priority, particularly as climate change could worsen water shortages in the medium to long term.
By 2030, SA is expected to have a 17% deficit between demand and supply of water, and in certain catchment areas this could be 40%.
Water was identified as the top risk by the private sector in the World Economic Forum’s Global Risk Report 2015 and unlike other risks, water was expected to increase in importance over the next decade.
Mr Naidoo said urbanisation and the densification of cities was expected to increase, and that this was already evident in Johannesburg and Sandton, where the wealthiest no longer lived in large, suburban mansions but in city apartments. If urban designers could make SA’s future megacities water sensitive, it would save having to retrofit them later.
Ana Deletic, professor of water engineering at Monash University, said after 14 years of drought, Melbourne in Australia has made significant strides in water recycling and harvesting storm water. A team of researchers at Monash has advised various cities, including in Australia, Israel and Singapore, on water-sensitive urban design.
This could be achieved by diversifying water sources, using dams, desalination, recycling of sewage and harvesting storm water.
Cities, including Johannesburg, currently produce more water than they consume. They could use this water by building green spaces that are also catchment and treatment areas, and putting “green walls” or creepers on high-rise buildings that can be used for recirculating grey water.
These systems not only increased water sources and used water more efficiently but would also help to cool inner cities where temperatures are magnified by reflected heat from glass and stone walls. They also provided attractive amenities, and green spaces could be used to grow food.
Prof Deletic said these shallow catchment areas could be built more cheaply than underground water and sewage pipelines and tunnels.
The biggest obstacle to installing them was that older cities were locked into the pipeline and tunnelling infrastructure built 200 years ago. But this was not the case for the cities emerging in Africa.