For all mankind’s technological advances, one thing we still can’t do is make it rain. Finding that solution is growing more urgent in many parts of the world, including the U.S. According to the World Wildlife Fund, two-thirds of the world’s population may face water shortages by 2025. One effort that researchers have been studying for decades is “cloud seeding” and more than 50 countries now have some sort of weather modification program that utilizes the still not-proven technology.
Cloud seeding as a scientific theory has been around since the 1940s when a researcher at General Electric discovered that he could make clouds form around blocks of dry ice under the right conditions. Further research revealed that silver iodide was even more effective than dry ice for “nucleating” or “seeding” clouds. In nature, clouds form from the condensation of invisible water vapor that is found on exceptionally small nuclei from dust, plan, pollution from cars, salt from ocean spray, etc. Cloud seeding increases the number of these available nuclei. This, in theory, should produce more rain. Chemicals may be dispersed by aircraft or by dispersion devices located on the ground.
At least eight states it the western U.S. have cloud seeding programs, most of which are shared projects between government agencies, utilities, and private businesses. It’s even part of official drought management strategies across the West, which is enduring one of the most intense dry spells on record. A $1.5 million program in the upper Colorado River Basin is split between state agencies in Colorado, Utah, Wyoming, Nevada, California, New Mexico, and Arizona under a pact formed in 2018. Most of the actual seeding is done by Upper Basin states which aim to increase winter precipitation in the mountains, in turn improving snowpack and increasing spring runoff.
Utah has what’s considered one of the most comprehensive weather modification efforts. In fact, every major mountain range in the state undergoes extensive cloud seeding. The seeding is done mostly by stationary generators that blast particles of silver iodide into the clouds. “There is way more water in clouds than actually falls to the ground,” explains Jake Serago, an engineer with the Utah Division of Water Resources. “And that’s because there’s a limit on the number of particles that the water can freeze to.” CNET has a good video showing how ground generators work. Many operations also use airplanes to drop in canisters of seeding material.
According to the state’s estimates, roughly 7% of the snowflakes that land on Utah’s major mountain ranges in any given winter are the product of cloud seeding. The Utah Division of Water Resources estimates the state’s cloud seeding led to an +8% jump in overall snowpack last year, and an average of +7% in previous seasons since the program began in 1973. Supporters say it’s one of the most cost-effective ways to boost runoff into the Colorado River Basin and the Great Salt Lake. However, atmospheric conditions have to be just right with clouds that are near or already precipitating. A 2019 study from Utah State University’s Climate Center found that fewer than 55% of precipitating clouds were suitable for cloud seeding.
China has an absolutely massive cloud seeding program covering over 2 million square miles, roughly half the countries landmass, or approximately two-and-a-half times the size of India. The country spends at least $200 million a year on the program, with plans to expand the area by about 38,000 square miles every year. The Chinese government says the main purpose is to ensure water for crops and cities, but it is also intended to break up hail storms. Officials claim seeding boosts precipitation by +8% to +15%.
Keri Nicoll, one of the core investigators on a project in the United Arab Emirates (UAE), thinks that a combination of cloud seeding and cloud “charging” could be even more effective. Her team from the University of Reading in the UK are set to begin testing small unmanned aircraft that zap clouds with an electric charge near Dubai. Each aircraft has sensors for measuring temperature, charge, and humidity, as well as charge emitters — the part that does the zapping. The idea is based on research that found when cloud droplets have a positive or negative electrical charge, the smaller droplets are more likely to merge and grow to become big raindrops.
Shooting an electric charge into clouds is a lot less expensive than seeding with silver iodide, which is very pricey. There are also questions as to whether seeding takes away rainfall from surrounding areas, as well as the environmental impacts of shooting silver iodide into the atmosphere. There are also still a lot of doubts about cloud seeding’s effectiveness as it is tough to prove that it creates an outcome that would not have happened without it. Simple statistical studies don’t prove that cloud seeding is actually causing heavier snowfall. That requires a more specialized scientific experiment and only within the last few years has the technology emerged to make that happen. Scientists are hopeful they’ll be able to answer many of the biggest questions still remaining about cloud seeding but it may take time and much more research. (Sources: Scientific America, CNN, The Economist, Lompoc Record)