The increased importance that people place on riparian vegetation for habitat and recreation further advises caution when considering vegetation management practices. This approach to increasing water supplies has generally fallen out of favor in Arizona. Weather Modification Advocates of weather modification look to the clouds as a source of water to augment current supplies. Arizona's interest in weather modification evolved over time, from early cloud seeding experiments to the adoption of sophisticated computer modeling techniques that simulate climatological phenomena and test weather modification premises. The evolution reflects a change in attitudes, from an optimistic expectation of immediate results to a more cautious, even skeptical regard about the potential of weather modification.
Clouds consist of small water droplets that, despite below-freezing temperatures, remain liquid.
The water's purity and the lack of foreign particles in the atmosphere prevent the droplets from freezing. As temperatures decrease, the droplets form ice crystals around small atmospheric particles such as dust. Cloud seeding introduces additional particles or nuclei into the atmosphere, causing more ice crystals to form. Silver iodide compounds or dry ice are the usual cloud seeding agents. Aircraft or ground-based generators introduce the agents into the atmosphere.