‘Global
weirding’: climate whiplash hitting world’s biggest cities, study reveals
Swings
between drought and floods striking from Dallas to Shanghai, while Madrid and
Cairo are among cities whose climate has flipped
Damian
Carrington Environment editor
Wed 12 Mar
2025 00.01 GMT
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.”
Flooding
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.
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.
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