Mexico hail storm: did climate change cause Guadalajara's freak summer ice?

Parts of the city were buried under a two-metre blanket of ice at the weekend only days after experiencing 30°C temperatures – but why?

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The city of Guadalajara buried beneath several feet of ice is hardly what most people would expect of summertime in Mexico.

Yet the metropolitan area of five million people about 560 kilometres north-west of Mexico City experienced an extreme hailstorm over the weekend, which damaged 200 homes, swept away vehicles and left local residents baffled – temperatures had been exceeding 30°C only days before.

The hailstorm caused significant disruption, blocking roads, but there were no reports of injuries. Enrique Alfaro Ramirez, governor of the state of Jalisco, of which Guadalajara is the capital, said he had “witnessed scenes that I have never seen before”.

The blanket of ice covering Guadalajara was two metres deep in places. But that hailstorms should happen in the summer is not as much a surprise as one might believe – they tend to be associated with thunderstorms, which are more common at warmers times of the year.

Professor Hayley Fowler, a hydroclimatologist and professor of climate change at Newcastle University in the United Kingdom, said hailstorms were actually typical in hot temperatures and around "thunderstorm-type events".
"You can get them [hailstorms] in the winter, but you do tend to get them with hotter temperatures."

But, she said, the one at the weekend was a particularly big one.

Hail forms during thunderstorms when water droplets are carried into the sky by upward warm air currents. The air cools as it rises, causing the droplets to freeze and, as they are moved up and down in the thunderstorm, to become larger.

Faster upward air currents create bigger hailstones, because only larger hailstones can overcome the upward currents and fall to earth.

Prof Fowler said that the amount of hail that fell in Guadalajara suggested that it may have been caused by a “mesoscale convective system”, which involves several thunderstorms coming together to form one large one. With such a larger storm, there is “extra air and moisture” involved.

“Normally convective systems are fairly small – they might be 1km or 2km. The mesoscale convective system can be really big, meaning you can get a lot more hail,” she said.

Governor Mr Ramirez raised the issue of whether there could be a link between this week's events and climate change while speaking to the media. And some research suggests he could be right – noting that thunderstorm activity would likely increase in the future, a 2017 study in the journal Nature Climate Change suggested that most parts of North America would experience "fewer hail days", but that the average size of the falls would increase.

Prof Fowler said that it was not possible to make a direct connection between the Guadalajara hailstorm and climate change because the technology that monitors it is not that sophist acted yet.

“There’s a bit of work looking at the incidence of hail. Certainly we’re expecting to see more of these convective storms in the future,” said Prof Fowler.