In centuries past, trading companies established shipping lanes—regularly trafficked routes for commercial vessels—based on prevailing winds and ocean currents. Commercial ships no longer use wind and sail for power, but many continue to travel those lanes. Two of the world’s busiest lanes—one running due west from the northern edge of Sumatra to the southern end of Sri Lanka in the Indian Ocean and one running northeast from Singapore into the South China Sea—happen to cut through two of the world’s rainiest regions.

If rain didn’t make life aboard cargo ships tough enough, the lanes also turn out to be particularly prone to thunderstorms. From 12 years of global lightning data, Joel Thornton, Todd Mitchell, and Robert Holzworth of the University of Washington and Katrina Virts of NASA’s Marshall Space Flight Center have found that lightning occurs above the two busy lanes twice as often as over adjacent regions.1 But...

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