15 percent in the target area. The second group of experiments confirmed the first, boosting rainfall 13 percent with only a 2.8 percent probability that the change was due to chance.
The Israelis succeeded by employing sound statistical techniques and good insights into cloud behavior-they estimated that cloudtop tem- peratures should be between -15�and -20�° for seeding to work. But luck is still a factor in such experiments. A 1979-80 U.S. Bureau of Reclamation test...