The 1975–1978 period has brought new realization that considerable atmospheric modification exists in the United States as a result of man's land use change [Weather Modification Advisory Board, 1978]. Cities, power plants, and certain agricultural activities modify the weather, often dramatically, on local and regional scales. Concern over these unintentional changes has grown nationally, making study of their nature and magnitude essential in many design and policy areas. Awareness of inadvertent weather modification has only recently become a part of wise planning for hydrologic, agricultural, transportation systems, and human activities.