Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain [source: Cotton]. Up to 100 times more ice crystals are used in dynamic cloud seeding than in the static method.
Experiments in cloud seeding suggest that it may be possible to artificially create rainfall. Rainfall occurs when supercooled droplets of water – those that are still liquid but are at a temperature below the usual freezing point of zero centigrade – form ice crystals.
Will China’s cloud-seeding efforts help to end its drought? If they are in a drought, they wouldn’t be able to draw enough from cloud seeding, just for the lack of clouds.
When clouds do not grow tall and cold enough to produce precipitation through the process of ice crystal growth (that occurs in mixed-phase clouds), it may be possible to stimulate precipitation by seeding these warm clouds with hygroscopic (water-absorbing) seeding agents.
Cloud seeding also depends heavily on environmental conditions like temperature and cloud composition. In 2003, the United States National Academy of Sciences declared that 30 years of studies had not produced “convincing” evidence that weather modification works [source: Associated Press ].
When water evaporates and rises into the atmosphere, it’s in gas form. Over time, this water vapor cools and condenses to become clouds. However, to condense, the vapor needs something to attach itself to. Drops of water or ice crystals do nicely for this.
So the message in all of this is that cloud seeding apparently works, but there’s a catch. First you’ve got to have clouds. Sometimes, during the worse droughts, there aren’t any clouds at all.
Augmenting Snowfall. Glaciogenic seeding can also be used to increase precipitation from stratiform and orographic clouds. In such cases, seeding may be accomplished through either ground-based or airborne modes. By increasing snowpack and resultant spring runoff, subsequent water supplies for hydropower are increased.