More than half of the world’s most populated cities are getting wetter, according to new research on how water patterns are undergoing dramatic shifts in urban areas as climate change intensifies the atmospheric effects.
The academic study involving Bristol and Cardiff universities, on behalf of aid group WaterAid, found that 52 per cent of cities showed a wetter trend over the past four decades, including Colombo, Mumbai and Kuala Lumpur.
At the same time, some 44 per cent of urban centres were getting drier, including Los Angeles, Riyadh, Paris and Cairo.
Scientists say climate change is leading to more intense rainfall, as every degree of warming of the atmosphere means it has the capacity to hold 7 per cent more water.
Equally, moisture is evaporating from the surface because of warmer temperatures, with some places “seeing a huge drying effect”, said Katerina Michaelides, lead scientist from the University of Bristol.
The “huge variability” in water patterns around the world made anticipating the effects a big challenge, she said.
“[Cities are] all changing in different ways. And so that the challenges that each city is facing are completely different and therefore would require a bespoke approach,” she said.
South Asian cities had made the most dramatic flip from drier to flood conditions. The study showed about 13 per cent of cities had flipped from a historically drier climate to extreme wet conditions, including Lahore in Pakistan and Bogotá in Colombia.
By contrast, cities such as Madrid and Hong Kong were among the 7 per cent of big urban areas in the study that had shifted from a wetter to an extremely dry climate.
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Europe’s ageing infrastructure meant many of the continent’s cities were increasingly vulnerable to the weather extremes.
However, it was the poorer cities across Asia and Africa that were most at risk from climate shifts, hitting access to clean water in urban areas already struggling with development challenges.
The study estimated one quarter of a billion people lived in cities that had shifted from one extreme to the other over the past 40 years, posing huge risks for urban populations and amplifying concerns about access to clean water.
“Climate whiplash” was experienced by 15 per cent of the world’s 100 most populous cities, including Hangzhou in China and Jakarta in Indonesia, as a result of an intensification of both droughts and floods.
Past research has found that weather-related disasters such as flooding and drought have increased by 400 per cent in the last 50 years, with 90 per cent of climate disasters driven by either too little or too much water.
Sol Oyuela, WaterAid’s executive director of global policy and campaigns, said four billion people globally already faced water scarcity.
The group has long warned of the consequences of so-called Day Zero — where a city runs out of water — which could push economies and security “to the brink”.
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