Half the world’s 100 largest cities are experiencing high levels of water stress, with 39 of these sitting in regions of “extremely high water stress”, new analysis and mapping has shown.
Water stress means that water withdrawals for public water supply and industry are close to exceeding available supplies, often caused by poor management of water resources exacerbated by climate breakdown.
Watershed Investigations and the Guardian mapped cities on to stressed catchments revealing that Beijing, New York, Los Angeles, Rio de Janeiro and Delhi are among those facing extreme stress, while London, Bangkok and Jakarta are classed as being highly stressed.
Separate analysis of Nasa satellite data, compiled by scientists at University College London, shows which of the largest 100 cities have been drying or getting wetter over two decades with places such as Chennai, Tehran and Zhengzhou showing strong drying trends and Tokyo, Lagos and Kampala showing strong wetting trends.
All 100 cities and their trends can be viewed on a new interactive water security atlas.
About 1.1 billion people live in major metropolitan areas located in regions experiencing strong long-term drying, compared with about 96 million in and around cities in regions showing strong wetting trends.
However, the satellite data is too coarse to show details and context at the local scale.
Most of the city regions in notably wetting zones are in sub-Saharan Africa, with just Tokyo and Santo Domingo in the Dominican Republic sitting elsewhere. Most of the urban centres in areas with the strongest drying signals are concentrated across Asia, particularly northern India and Pakistan.
Now in its sixth year of drought, Tehran is perilously close to “day zero” when no water will be available for its citizens, and last year the country’s president, Masoud Pezeshkian, said the city may have to be evacuated if the drought continues. Cape Town and Chennai have both come close to day zero and many of the world’s fastest-growing cities are situated in drying zones where they could experience future water shortages.
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Mohammad Shamsudduha, professor of water crisis and risk reduction at UCL, said: “By tracking changes in total water storage from space, [the Nasa project] Grace shows which cities are drying and which are getting wetter, offering an early warning of emerging water insecurity.”
On Tuesday the UN announced that the world had entered a state of water bankruptcy where deterioration of some water resources had become permanent and irreversible. Prof Kaveh Madani, director of the United Nations University Institute for Water Environment and Health, said poor management of water is frequently the main cause of bankruptcy and that climate breakdown is seldom the sole reason: “Climate change is like a recession on top of bad management of business.”
The World Bank Group has also been sounding the alarm. Global freshwater reserves have plunged sharply over the past 20 years, according to the group, which says the planet is losing about 324bn cubic metres of freshwater every year, enough to meet the annual needs of 280 million people, or roughly the population of Indonesia. The losses affect major river basins on every continent.
