Earth Notes: Seeding the Clouds

Feb 18, 2015

  For generations western farmers have worried about getting enough water from the sky to nourish their crops. Some have tried to do something about it.

A century ago farmers in places like the Great Plains and California hired specialists who claimed they could water the land by shooting explosives into the sky or by releasing secret mixtures of chemicals. Sometimes it did rain then. Sometimes it didn’t—in which case the would-be rainmakers typically left town fast.

Today electric utilities and irrigation districts in several western states take a more scientific approach. When a winter storm approaches, they use aircraft or ground-based equipment to seed the clouds with silver iodide particles that can promote the formation of snowflakes. Proponents claim that can increase winter snowpacks.

Cloud seeding is a multimillion-dollar business across the West. Still, scientists debate its efficacy. But a new study out of Wyoming represents the most detailed effort yet to quantify the results.

Credit National Center for Atmospheric Research

Scientists from the University of Wyoming and the National Center for Atmospheric Research spent six winters studying the practice in Wyoming. By examining two parallel mountain ranges—one seeded with particles, the other not—they came to the conclusion that cloud seeding does produce a small but measurable increase in snowfall.

But weather patterns are complex and unpredictable. Further, cloud seeding raises tough questions about liability for heavy snowfall and about who controls precipitation. For now, it’s likely to remain only a minor part of how people in the West deal with an arid climate.

Earth Notes is produced by KNAU and the Sustainable Communities Program at Northern Arizona University.