Weather warfare is the use of weather modification techniques such as cloud seeding for military purposes.
Prior to the Environmental Modification Convention signed in Geneva in 1977, the United States used weather warfare in the Vietnam War. Under the auspices of the Air Weather Service, the United States' Operation Popeye used cloud seeding over the Ho Chi Minh trail, increasing rainfall by an estimated thirty percent during 1967 and 1968. It was hoped that the increased rainfall would reduce the rate of infiltration down the trail.
https://en.wikipedia.org/wiki/Weather_warfare