These two U.S. cities are the most vulnerable to severe space weather

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"We have identified certain regions of the U.S.—Washington D.C. area and Milwaukee—which are repeatedly appearing as 'highly connected' in our network, hence are possibly regions particularly vulnerable to the effects of space weather and may benefit from further monitoring," said Dr. Lauren Orr of the BGS, who presented her findings at last week's National Astronomy Meeting at the University of Hull in the U.K.

Using network science to work out the resilience of the power grid across the U.S. the researchers found "supernodes" most at risk, which appear to be Washington, D.C. and Milwaukee. "These areas could be modified during a geomagnetic storm to prevent transformers burning out and to limit damage to the wider power grid," said Orr.

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The worst case ever recorded was on Sept. 2, 1859, when the so-called Carrington Event—a massive solar flare—gave electric shocks to telegraph operators. According to a study, if that happened now, it could cause over $41.5 billion in economic loss per day in the U.S.

Previous research by the British Geological Survey revealed that May 10's geomagnetic storm was the most extreme and long-lasting recorded in the U.K. in the last 155 years—and possibly for the last 500 years.