Storm Surge

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Published in the September 2015 issue of National Geographic magazine

A novel storm formula is shedding new light on lightning. While researching cloud behavior, the University of California, Berkeley’s David Romps and colleagues devised what they say is the most accurate model yet for predicting lightning strikes. Then they used that model to project how strikes will multiply—and how that could lead to more wildfires—if the planet continues to warm.

For a storm to produce the sudden electric discharge known as lightning, liquid water and ice, plus updrafts fast enough to keep both suspended, must be present. Romps theorized that by putting those factors into an equation, he could calculate how often lightning would strike. He multiplied the measured precipitation by the convective available potential energy, or how fast a storm cloud can rise. His calculations using 2011 data matched recorded lightning strikes 77 percent of the time. The conventional model was only 39 percent accurate.

The warmer the air is, the more storm-fueling water vapor it can hold. For every degree Celsius that the world warms, lightning strikes may increase about 12 per- cent in the U.S., Romps says. If carbon dioxide emissions continue at the current rate, that could mean 50 percent more lightning strikes by 2100.

—Lindsay N. Smith

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