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Climate whiplash is already hitting major cities around the world, bringing deadly swings between extreme wet and dry weather as the climate crisis intensifies, a report has revealed.
Dozens more cities, including Lucknow, Madrid and Riyadh have suffered a climate “flip” in the last 20 years, switching from dry to wet extremes, or vice versa. The report analysed the 100 most populous cities, plus 12 selected ones, and found that 95% of them showed a distinct trend towards wetter or drier weather.
The changing climate of cities can hit citizens with worsened floods and droughts, destroy access to clean water, sanitation and food, displace communities and spread disease. Cities where the water infrastructure is already poor, such as Karachi and Khartoum, suffer the most.
Cities across the world are affected but the data shows some regional trends, with drying hitting Europe, the already-parched Arabian peninsula and much of the US, while cities in south and south-east Asia are experiencing bigger downpours.
The analysis illustrates the climate chaos being brought to urban areas by human-caused global heating. Too little or too much water is the cause of 90% of climate disasters. More than 4.4 billion people live in cities and the climate crisis was already known to be supercharging individual extreme weather disasters across the planet.
Rising temperatures, driven by fossil fuel pollution, can exacerbate both floods and droughts because warmer air can take up more water vapour. This means the air can suck more water from the ground during hot, dry periods but also release more intense downpours when the rains come.
“Our study shows that climate change is dramatically different around the world,” said Prof Katerina Michaelides, at the University of Bristol, UK. Her co-author, Prof Michael Singer at Cardiff University, described the pattern as “global weirding”.
“Most places we looked at are changing in some way, but in ways that are not always predictable,” Singer said. “And given that we’re looking at the world’s largest cities, there are really significant numbers of people involved.”
Coping with climate whiplash and flips in cities is extremely hard, said Michaelides. Many cities already face water supply, sewage and flood protection problems as their populations rapidly swell. But global heating supercharges this, with the often ageing infrastructure in rich nations designed for a climate that no longer exists, and more climate extremes making the establishment of much-needed infrastructure even harder in low income nations.
The researchers have worked in Nairobi, Kenya, one of the cities suffering climate whiplash. “People were struggling with no water, failed crops, dead livestock, with drought really impacting their livelihoods and lives for multiple years,” Michaelides said. “Then the next thing that happens is too much rain, and everything’s flooded, they lose more livestock, the city infrastructure gets overwhelmed, water gets contaminated, and then people get sick.”
Sol Oyuela, executive director at NGO WaterAid, which commissioned the analysis, said: “The threat of a global ‘day zero’ looms large – what happens when the 4 billion people already facing water scarcity reach that breaking point, and the food, health, energy, nature, economies, and security that depend on water are pushed to the brink?”
“Now is the time for urgent collective action, so communities can recover from disasters and be ready for whatever the future holds. This will make the world a safer place for all,” Oyuela said.
The savage wildfires in Los Angeles in January were an example of a single whiplash event, with a wet period spurring vegetation growth, which then fuelled the fires when hot and dry weather followed. Such events are increasing due to human-caused global heating.
The new analysis by Michaelides and Singer was much broader and examined the changes in wet and dry extremes over the past four decades in 112 major cities.
It found that 17 cities across the globe have been hit by climate whiplash, suffering more frequent extremes of both wet and dry conditions. The biggest whiplashes were seen in Hangzhou in China, the Indonesian megacity of Jakarta, and Dallas in Texas. Other whiplash cities include Baghdad, Bangkok, Melbourne and Nairobi. The rapid shift between wet and dry extremes makes it difficult for cities to prepare and recover, damaging lives and livelihoods.
The analysis also found that 24 cities have seen dramatic climate flips this century. The sharpest switches from wet to dry conditions have been in Cairo, Madrid and Riyadh, with Hong Kong and San Jose in California also in the top 10. Prolonged droughts can lead to water shortages, disrupted food supplies and electricity blackouts where hydropower is relied upon.
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The sharpest switches from dry to wet conditions were in Lucknow and Surat in India and in Nigeria’s second city, Kano. Other cities with wet flips were Bogotá, Hong Kong and Tehran. Intense rains can cause flash floods, destroying homes and roads and spreading deadly waterborne diseases like cholera and dysentery when sanitation systems are overwhelmed.
The researchers also assessed the level of social vulnerability and quality of infrastructure in the cities. The cities with the biggest increases in climate hazards combined with the highest vulnerability – and therefore the places facing the greatest dangers – were Khartoum in Sudan, Faisalabad in Pakistan, and Amman in Jordan.
Karachi, also in Pakistan, ranked highly for vulnerability as well and is experiencing more wet extremes. Torrential rains in 2022 destroyed the family home of fisher Mohammad Yunis in Ibrahim Hyderi, a waterfront district in the city.
“We have spent many days and nights completely drenched in rain because we had no shelter,” he said. “The weather affects everything. When it rains heavily, our children fall sick. But we don’t have sufficient [clean] water. Our localities are breaking down. Houses near the drainage systems collapse due to floods. When floods come, walls fall apart. If we had enough money, we would not be living here.”
Even in the cities where the changes in climate were less stark, clear trends were seen in almost all of them. The places getting drier over the last 40 years included Paris, Los Angeles, Cape Town, and Rio de Janeiro. Many of those getting wetter are in south Asia, such as Mumbai, Lahore and Kabul.
The researchers also found 11 cities where the number of extreme wet or dry months had fallen in the last 20 years, including Nagoya in Japan, Lusaka in Zambia, and Guangzhou in China.
The overall results of the new study are consistent with the most recent report from the Intergovernmental Panel on Climate Change, which found there were both regions with increases in heavy rains and others with increases in drought, as well as some regions with increases in both, said Prof Sonia Seneviratne, at ETH Zurich in Switzerland, coordinating lead author of the IPCC chapter on weather and climate extreme events.
“A few tenths of a degree warmer and the life we know becomes increasingly at risk due to climate extremes such as heatwaves, droughts, and heavy rainfall,” she said.
Singer said: “We hope our report can galvanise global attention on the challenges of climate change with respect to water. Perhaps it will lead to a more realistic conversation about supporting adaptation to climate change, with a sense of compassion and understanding of the challenges people are facing, rather than just saying, well, we can’t afford it.”
Methodology
The researchers analysed the changing climate of cities using a standard index (SPEI) that combined precipitation with evaporation each month from 1983 to 2023. Index values above a widely-used threshold were categorised as extreme.
To assess changes over the four decades, the data was split into two 21-year periods. The cities that experienced at least 12 months more of one type of extreme climate (wet or dry) and at least 12 months less of the other type of extreme climate in the second 21-year period were classed as having a climate flip. The cities that had at least five months more of both extreme wet and extreme dry in the second period were classed as having developed climate whiplash. The overall wetting or drying trends were determined from all 42 years of data.
The population data used to determine the 100 most populous cities was based on population density, not the administrative boundaries of the city, and therefore are a truer reflection of the city’s size. Social vulnerability was measured using the standard Human Development Index and the water and waste infrastructure data was taken from a global dataset published in 2022.
