Flooded by the Nile for thousands of years, Cairo is facing increasingly severe drought as the world's most extreme example of a phenomenon called "climate flip".
Riyadh, Jeddah and Khartoum are also in the grip of "drying trends" as the Middle East and North Africa take a pounding from climate change, a major study has found. Scientists working for the charity WaterAid have identified 24 "flip" cities where floods are turning to drought, or droughts to flooding, as the Earth's atmosphere changes.
In other cities such as Amman, a tendency for dry conditions is only getting worse, while floods are intensifying in parts of the Indian subcontinent. Baghdad is in the top five cities experiencing "climate whiplash" – where both extremes are occurring more often.
"In South-east Asia, we're seeing very strong wetting trends and a predominance of cities that are flipping towards extreme wet conditions," said Katerina Michaelides, a University of Bristol hydrologist who co-wrote WaterAid's report. "That's a very strong regional pattern that emerged and a lot of the most populous cities in the world are clustered in that region.
"A second cluster that we're seeing emerging is the Middle East, the Arabian Peninsula and North Africa, [which] are showing a very strong drying trend," she told The National. "Those are already regions that are historically dry, but they're trending towards even drier conditions, deeper, more intense droughts, longer-lasting droughts."
Why the 'flip'?
The "climate flip" cities have, over the past two decades, endured at least 12 months more than usual of one kind of wet or dry extreme, and 12 fewer months of the other.
Cairo is the most severe case, enduring "extreme dry" conditions far more often than before, while "extreme wet" months are less common. Adding to Egypt's water scarcity problems is a long-running row with Ethiopia about the building of a dam on the upper Nile.
Prof Michaelides said the explanation for the "climate flip" could be that as the Earth's atmosphere is dried out by global warming, it retains more moisture than it should, then scatters it elsewhere.
"In some places, more water will leave the surface," she said. "Some places will see drying because the atmosphere above that place can hold a lot more moisture. That moisture that's in the atmosphere has to move somewhere. It very rarely stays in the same place and then releases that moisture back down. It tends to move with the global wind patterns."
Madrid, Riyadh, Hong Kong and Jeddah are behind Cairo in the top five "drying" cities. Lucknow, in India, is the prime example of the opposite "wetting trend", followed by Surat in Thailand and Kano in Nigeria.
Social vulnerability
WaterAid's research is being shared this week with senior officials and environmentalists in Britain. Its study of 112 of the world's biggest cities warns that those facing the most severe wrath from nature are often also highly exposed for social and economic reasons.
"There are hotspots emerging," said Prof Michaelides. "Parts of South Asia are in that category; parts of the Middle East [such as] Iraq; also parts of Africa like Sudan, which is compounded by conflict of course, and social vulnerability and infrastructure vulnerability.
"From a country perspective, the challenges are that every city is unique in many ways. They have to look at their own climate profile and their underlying vulnerabilities, and try to assess how to best adapt to these kinds of conditions. That's not an easy thing.
"Cities are like oil tankers in many ways. It's hard to really manipulate policy and governance and infrastructure quickly to adapt to these things. But at least having this information, every city can start to look at their profile and potentially with other cities ... can sit and look at what the adaptation strategies might look like."
