Sunday, February 22, 2015

Big Cities Head for Water Crisis as Populations Explode

Water pots waiting to be filled from a street tap in Chennai, India. (Credit: McKay Savage via Wikimedia Commons) Click to Enlarge.
More than 40% of the world’s great cities supplied by surface water could become vulnerable to shortages and drought by 2040, according to new research.  And more than three out of 10 were already vulnerable in 2010.

Meanwhile, the vital array of satellites designed to monitor rainfall and to warn of potential flooding is reported to be coming to the end of its shelf life.

For the first time in history, more than half the world’s population is now concentrated in cities, and this proportion is predicted to increase to two-thirds.  Cities grow up near plentiful water supplies − and as a population explodes, so does demand.  But the flow remains much the same.

Some cities are already under drought stress.  Chennai in southern India had to be supplied with tankers in 2004 and 2005, and São Paulo in Brazil is now at crisis point.

Supply analysis
Environmental scientist Julie Padowski and Steven Gorelick, director of the Global Freshwater Initiative at Stanford University in California, report in Environmental Research Letters that they analysed supplies to 70 cities in 39 countries, all of them with more than 750,000 inhabitants, and all of them reliant on surface water.

They defined vulnerability as the failure of an urban supply basin to meet demands from human, environmental and agricultural users, and they set the supply target as 4,600 litres per person per day – which factors in “virtual water”, defined as the total volume of water needed to produce and process a commodity or service.
Importantly, the scientists did not factor in climate change, which is likely to make conditions worse.  Instead, they simply considered current demand and supply, and then projected demand in 2040.
The six cities that will begin to face water shortages are Dublin in Ireland, Charlotte in the US, Ouagadougou in Burkina Faso, and Guangzhou, Wuhan and Nanjing in China.

Read more at Big Cities Head for Water Crisis as Populations Explode

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