Weather modification has a rather unique status among water resource issues. Along with attracting attention as a potential water supply source, weather modification is of interest because of its varied and changing status in the scientific and public policy communities. Weather modification is a sector of Meteorology dealing with cloud seeding, as an environmentally friendly technology, that helps clouds more efficiently produce precipitation in the form of rain or snow, or reduce hail generated by thunderstorms, or dissipate fog. From all these, the most beneficial and ambitious is to initiate or increase precipitation, in other words, the precipitation enhancement methodology. This well-established technology has been in use since 1940s in several countries around the world. After Vonnegut's (1947) discovery of the AgI crystal formations, the first effort to seed clouds using ice nuclei was made by Kraus and Squires in 1947 (Mason 1971).
There is considerable evidence that, under certain conditions, precipitation from properly selected clouds can be increased with the existing techniques on the order of 10 to 15%. Field measurements, numerical model simulations and proper seeding technologies could very well support increases of this percentage. The processes culminating in increased precipitation have recently been directly observed during conducted seeding experiments. While such observations further support statistical analyses, they have to date been of limitless scope, and thus the economic impact of the increases can be assessed.
The effects of climate change and the continued increase in water needs, for both urban and agricultural use, have largely exhausted water supplies; therefore, an effort must be taken in order to find new ways to augment them. The methods of enhancing water resources of an area are divided into conventional, such as: dams, water reservoirs, adaptation of new cultivations (in agriculture) and non-conventional, such as: precipitation enhancement. In recent years, the development of new sophisticated atmospheric models, in conjunction with modern instruments for recording and measuring atmospheric and cloud physics data have increased the interest for weather modification, and particularly for precipitation enhancement projects (Silverman 2003).
According to the World Meteorological Organization's (WMO) interest in precipitation enhancement programs increases due to:
- New equipment and recording techniques from aircraft data, weather radar, satellites and ground automated weather stations
- New seeding material for more cloud types and seeding conditions
- Use of new, sophisticated high-resolution numerical weather prediction models and processing software packages
- New methods of assessing results
Moreover, in recent years, 24 countries are operationally conducting precipitation enhancement projects with encouraging results, according to the World Meteorological Organization (WMO). In the USA, 21 precipitation enhancement projects are being conducted.
Mason, B. J., 1971: The Physics of Clouds. Clarendon Press, Oxford, pp 671.
Silverman, B. A., 2003: A Critical Assessment Of Hygroscopic Seeding Of Convective Clouds For Rainfall Enhancement. Bulletin of the American Meteorological Society, 1219-1230.
Vonnegut, B., 1947: The Nucleation of Ice Formation by Silver Iodide. J. Applied Physics, Vol. 18, 593-595.