Who says the agronomy guys get to have all the fun when it comes to seeding? We
weather types can get into the action—if only marginally—through cloud
seeding. Its actual impact is negligible, but that doesn't keep us from trying.
Cloud seeding got its start in the mid-1940s. The idea was developed by
scientist Bernard Vonnegut (author Kurt Vonnegut's brother). Seeding was first
put into action by another scientist, Vincent Schaefer. Both men were scientists
with General Electric.
Seeding is simply the process of depositing a load (or several loads) of dry ice
to promising-looking storm clouds in an effort to beef up raindrop formation.
Silver iodide is generally used as the celestial fertilizer. The chemistry
behind this infusion of dry ice is that ice crystals provide a surface for water
droplets to attach. When the drops get big enough, gravity takes over and the
raindrops fall out of the cloud.
This practice is called the "cold rain" process. It works with the atmospheric
chain of events for the majority of rainstorms in the United States. There's
another process called the "warm rain" process, which involves clouds in
tropical weather systems.
STILL USED TODAY. Hurricanes, El Niño and climate change may have elbowed cloud
seeding from the news headlines, but, in fact, this effort is very
active—especially in the Plains and the interior West, where rainfall is at the
top of everyone's wish list.
Eleven states and the Canadian province of Alberta pay for a periodic booster
shot into storm systems. Cloud seeding has been tried and studied in Mexico,
Thailand, Italy, Argentina and Australia. But China has the world's largest
cloud-seeding system. (More on China later.)
The skies over about 11 million acres in west Texas are seeded on a regular
basis when promising storm systems appear. It's a project that has gone on for
more than 10 years. These efforts have produced increased rainfall of anywhere
from 34 to 130% above long-term averages.
There's also another benefit: The additional crystals shot into the clouds
compete with the hail seeds (or "embryos") for the available cloud moisture.
With the ice crystals using more of the available cloud droplets to grow large
raindrops, there is less cloud moisture available to grow the embryos into
damaging hailstones.
CHINESE FORTUNES. You'll probably read and hear more about cloud seeding during
the summer of 2008 when the Olympics get under way in Beijing. The event is a
huge opportunity for the Chinese government to showcase the country to a
worldwide TV audience that may well top 1 billion viewers.
There's a big problem, however. The East Asia sky is hazy with few
"bluebird"-type days and sunshine-filled skies. The Chinese authorities plan to
help the cause, however, through strategic cloud seeding if storm clouds form in
the hills west of Beijing.
A battery of anti-aircraft guns is already in place to launch canisters
containing silver iodide into clouds that form in the days before the Olympic
opening ceremonies. The plan is to drain the haze and dust out of the Beijing
skies. There will be no rain on the Olympic parade if the Chinese government has
anything to say about it.
So whether it's for better yield or better aesthetics, cloud seeding will
continue to be an ongoing, yet somewhat limited, feature of storm-related
activity as we farm the earth and sky. But there's one big difference in farming
the sky: I don't think it matters whether the pilots of cloud-seeding planes fly
in a perfectly straight line.