Cloud seedingIf the Rain Dancing ceremony suddenly doesn't work for you anymore, you might consider using a cloud seeding technique to bring back the rain. Cloud seeding represents a form of weather modification, in the attempt to change the amount or type of precipitation that falls from the clouds, by spreading substances in them that will serve as cloud condensation of ice nuclei.
The usual purpose of cloud seeding is to increase or to trigger precipitation, to prevent droughts. Rain is triggered by introducing into the cloud chemicals like silver iodide or dry ice (solid carbon dioxide). Silver iodide is mostly used for winter snowfall augmentation and hail suppression. The first attempt to seed clouds was made in 1946 by Vincent Schaefer, a General Electric chemist when after dropping six pounds of dry ice into a cloud, which triggered a snowfall near Schenectady in the upstate of New York.
But without suitable clouds, there's no chance of producing hardly any rain. Right now, the southeast of the United States is suffering from a drought which threatens to leave a couple of millions of people without water. Though the possibility of triggering rain is remote due to the absence of clouds, the method has been successfully implemented in the wintertime when the snowfall in the mountain regions was increased up to twenty percent, thus producing an extra runoff when the snow melted in the spring.
The method could be used in other areas, whether during the winter season, or the rest or the year. Due to the fact that mountain clouds are low-level clouds, these can be better understood, but regions like that in the southeast of the US receive large amounts of rain all year long, so this advantage can be used by researches to make them pour.
The principle behind the cloud seeding process is actually very simple, the chemicals which are injected into the clouds provide small particles on which water vapor can condense. As more and more vapor condenses on a particle, it gets heavier and falls down to the surface of the Earth under its own weight, thus creating rain. Such hydroscopic materials, meaning that they absorb water, are being developed to improve the performance. Certain hydroscopic flares offer a lot of the seeding material and are more effective over wide ranges of temperatures, and different types of clouds.
Critics say that increasing the rainfall in some areas has the disadvantage that of decreasing the amounts of precipitation in other regions. Scientists say that the phenomena is not very well known, but the chance of that happening is remote.
China is one of the countries in which cloud seeding is a wide spread method to trigger rain, over vast areas affected by drought. The same method is planed to be used to clear the air of pollution, with the help of the rain before the 2008 Olimpics. China has been accused in the past by neighboring countries that they are stealing the clouds.