Cloud seeding is a weather modification technique that introduces nucleating agents into clouds to encourage precipitation. Silver iodide and dry ice are the most commonly used seeding materials.
Cloud seeding is a form of intentional weather modification in which substances such as silver iodide (AgI), potassium iodide, or dry ice (solid CO2) are dispersed into clouds to provide additional condensation or ice nuclei around which water droplets or ice crystals can form, potentially enhancing precipitation. Silver iodide is preferred because its crystalline structure closely resembles that of natural ice, making it an effective ice nucleus at temperatures below -5 degrees Celsius. Seeding agents can be delivered from aircraft flying through or above target clouds, or from ground-based generators positioned upwind of mountain barriers. Cloud seeding programs have been implemented in numerous countries including the United States, China, United Arab Emirates, Australia, and Israel, primarily for augmenting water supply, reducing hail damage, and dispersing fog. Scientific assessments suggest that cloud seeding can increase precipitation by 5-15 percent under favorable conditions, though the effectiveness varies with cloud type, temperature, and existing moisture content. The technology requires naturally occurring clouds with sufficient moisture; it cannot create precipitation from clear skies. Environmental concerns include potential redistribution of precipitation from downwind areas, accumulation of silver compounds in ecosystems, and the ethical implications of weather modification.