Around half the surface water supply in central Arizona comes from melting snowpack on the Mogollon Rim. Three decades ago, the use of cloud seeding to enhance precipitation over the region was tested as part of a large field experiment.
It was called the ‘1995 Arizona Program.’ From January 15th to March 15th that year, twenty-nine scientists from eight institutions used Doppler radars, an instrumented airplane, and other sensors, to better understand the dynamics of winter storms over the Verde Valley and surrounding mountains.
Researchers were especially keen to investigate the potential of using so-called ‘gravity waves,’ which form when air flows up over mountains, to boost precipitation over high ground.
Crystals of silver iodide and very fine particles of common salts were released by aircraft six different times, and one additional time from the top of Mingus Mountain.
No significant increase in precipitation was measured at ground level, likely due to the limited number of seeding experiments that were possible. But the observations and data collected supported the researchers’ models of how cloud seeding works, and suggested that the technique potentially could increase precipitation from storms with high moisture content.
More recent research at the University of Wyoming has directly observed as much as a 10 to 15 percent increase in precipitation from such enhancement. Modern cloud seeding methods mostly use ground-based generators and drones, over watersheds and ski resorts in Colorado and Utah, where boosting snowpack this way is considered economically viable.
This Earth Note was written by Diane Hope, and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
