Katerina Michaelides

If a city can see that they're in a climate change pattern that produces these whiplash effects, then it provides enough insight and information to try and begin to adapt to these things.

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Basically, our research shows how climate has been changing over the last four decades in the 100 most populated cities in the world. That amounts to just under 20% of the global population, and it considers the implications for water security. We analyzed this through a monthly index of wetting and drying.

And from that, we derived specific metrics that tell us important information about how climate hazards such as flooding and drought are changing over time. And when we look at that over these 100 cities, we find that climate is changing dramatically around the world, but in different ways.

So some of the ways are this whiplash effect, which is basically an intensification of both extreme dry and extreme wet periods. Around 15 percent of our cities are in this pattern of climate whiplash. So places like East Africa, southern United States, China, Australia, Middle East.

And this is quite an important phenomenon because, in a sense, the way that people are battered between two extremes, you either have too much water or not enough water. And that whiplash between these two extremes presents huge challenges for people, for cities. And the context of the city here is particularly important because these urban centres are constrained by their existing infrastructure.

So global atmospheric warming is definitely a key factor in this. As global temperatures are rising, the atmosphere can hold more moisture in it. So on the one hand, what that means is it has capacity to remove more moisture from the surface of the Earth. So in cases where that's happening a lot, that's causing extreme drying.

That moisture then in the atmosphere is being moved around the world through global patterns of winds. And the place which receives all that moisture is then experiencing that intense wetting.

Absolutely. So there's two factors underlying the ability of a city to be resilient to these extreme climatic episodes. One is the underlying socioeconomic status and the infrastructure capability. So when we combine these extreme climatic changes with the underlying infrastructure and social vulnerability issues, we see some hotspots emerging around the world.

And these are cities in South and Southeast Asia, specifically Pakistan and India, as well as countries in East Africa and the Middle East.