A new global analysis has found that half of the world’s 100 largest cities are now located in regions facing high levels of water stress, raising fresh concerns over urban water security amid worsening climate pressures and poor resource management.
An investigation by Watershed Investigations in collaboration with The Guardian mapped major cities against stressed river catchments and water systems. The findings show that 39 of the world’s biggest urban centres are situated in areas of “extremely high water stress,” where water demand for households and industry is close to exceeding available supplies.
Cities such as Beijing, New York, Los Angeles, Rio de Janeiro and Delhi are among those experiencing the most severe pressure. London, Bangkok and Jakarta have been classified as highly stressed. Water stress occurs when withdrawals approach or surpass sustainable limits, often driven by inefficient governance and compounded by climate breakdown.
Alongside this mapping exercise, scientists at University College London analysed two decades of Nasa satellite data to track changes in water storage across major cities. Their research reveals clear long-term drying trends in places such as Chennai, Tehran and Zhengzhou, while cities including Tokyo, Lagos and Kampala show strong wetting patterns. The full findings have been compiled into a new interactive global water security atlas.
The data suggests that around 1.1 billion people live in metropolitan areas located in regions undergoing sustained drying, compared with approximately 96 million people in areas experiencing increased moisture. Researchers caution, however, that satellite data lacks the resolution to capture local conditions in detail.
Most cities showing wetting trends are located in sub-Saharan Africa, with Tokyo and Santo Domingo in the Dominican Republic as notable exceptions. In contrast, many of the fastest-drying urban centres are concentrated across Asia, particularly in northern India and Pakistan.
Some cities are already approaching critical thresholds. Tehran, now in its sixth year of drought, is nearing “day zero,” the point at which municipal water supplies may collapse. Last year, Iran’s president Masoud Pezeshkian warned that the capital might need to be evacuated if the crisis deepens. Cape Town and Chennai have previously faced similar risks, highlighting how rapidly growing cities in drying regions remain vulnerable to future shortages.
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.”
The findings come as global institutions issue increasingly stark warnings. This week, the United Nations declared that the world has entered a state of “water bankruptcy,” in which the degradation of some water resources has become permanent and irreversible.
Prof Kaveh Madani, director of the United Nations University Institute for Water Environment and Health, said mismanagement remains a central factor. “Climate change is like a recession on top of bad management of business,” he said.
The World Bank Group has also raised concerns, reporting that global freshwater reserves have fallen sharply over the past two decades. The planet is now losing around 324 billion cubic metres of freshwater annually—enough to meet the needs of roughly 280 million people, equivalent to Indonesia’s population. Major river basins on every continent have been affected.
In the UK, the outlook is equally troubling. By 2055, England may need an additional 5 billion litres of water per day for public supply—more than a third of current usage—according to the Environment Agency. Agriculture and energy sectors could require another 1 billion litres daily.
Shamsudduha said that “the ‘hidden resource of groundwater offers the UK a more climate-resilient water supply,” but warned that “without sustained monitoring and better management we risk managing it blindly amid intensifying development and climate pressures.”
Recent water outages in parts of southern England, which South East Water attributed to winter storms, have intensified scrutiny. Regulators had previously raised “serious concerns” about the company’s supply security.
Against this backdrop, the government has released a new water white paper proposing major reforms, including the creation of a chief engineer role, mandatory “MOT checks” for water infrastructure, and expanded powers for a new regulator.
The latest analysis underscores how mounting climate pressures, governance failures and rapid urbanisation are converging to threaten water security for billions of people in the decades ahead.
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