A review of cloud seeding experiments to enhance precipitation and some new prospects

Water is one of the most basic commodities on earth sustaining human life. In many regions of the world, traditional sources and supplies of ground wa ter, rivers and reservoirs, are either inadequate or under threat from ever -increasing demands on water from changes in land use and growing populatio ns. This has prompted scientists and engineers to explore the possibility o f augmenting water supplies by means of cloud seeding. This paper provides an overview of the current scientific status of weather modification activities to enhance precipitation for both glaciogenic and hygroscopic seeding experiments. It is important to emphasize that although funding for scientific studies has decreased substantially during the past decade, operational programs have actually increased. During the last 10 years there has been a thorough scrutiny of past experim ents involving experiments using glaciogenic seeding. Although there still exist indications that seeding can increase precipitation, a number of rece nt studies have questioned many of the positive results, weakening the scie ntific credibility. As a result, considerable skepticism exists as to wheth er these methods provides a cost-effective means for increasing precipitati on for water resources. Recent results from hygroscopic seeding experiments provided for some renew ed optimism in the field of precipitation enhancement. Although promising r esults have been obtained to date, some fundamental questions remain that n eed to be answered in order to provide a sound scientific basis for this te chnology.