ILLINOIS WATER SUPPLY
Illinois Cloud Seeding Projects
Farmers in the Vandalia area raised funds to hire a cloud-seeding firm for a project in summer 1963.
Ground-based generators were used.
At the end of the project, the summer rainfall total at the Weather Service raingage in Vandalia was slightly higher than in raingauges in surrounding counties.
During 1969–1980, farmers in four Illinois areas raised funds for cloud-seeding projects over two summers (Vermilion County) and three summers (McLean County, Mattoon area, and Harrisburg area).
Reputable cloud-seeding firms were hired to deliver AgI at cloud bases. Each project involved establishing a seeding headquarters at a local airport in the project area, staff to forecast rain conditions and direct operations, two piloted airplanes equipped with AgI burners, and a radar to guide the planes to approaching showers.
Annual costs for each project ranged from $85,000 to $100,000 (1980 dollars), or over $1 million to support the 11 project years of operations in Illinois.
Using raingauge data and radar data to evaluate project results, ISWS scientists calculated rainfall increases of 10 percent in the seeded areas in most years but no increase in a few years.
Federal funding was used to start the costly project in 1971, but agency budget reductions ended the support before field tests got underway.
Adequate funding became available in 1984, and field tests were conducted in the summers during 1986–1990.
An airplane randomly seeded the AgI into growing cumulus clouds so that both seeded and unseeded clouds were available for comparison.
A sophisticated Doppler weather radar measured precipitation growth inside the cloud before and after seeding, and also the amount of rain deposited on the ground by the individual clouds.
Certain types of cumulus clouds produced 5 to 15 percent more rain when seeded than unseeded clouds of the same type.
Current interest in cloud seeding in Illinois is low, even though modest increases in summer rain are possible.
Many potential sponsors think that the substantial project costs do not outweigh the benefits of receiving slightly more rain.
This situation could change if the economy improved and value of the added rainfall was perceived to exceed the project costs.