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a. Impacts of agricultural practices <br /> Variations in cropping and irrigation practices are known to alter local albedos,humidity, surface temperatures, <br /> and roughness. Large-scale irrigation projects alter boundary-layer conditions, increasing the potential for <br /> precipitation. Overgrazing of large grasslands and large-scale deforestation reduce evapotranspiration and <br /> change the surface roughness, altering the moisture, temperature, and winds in the boundary layer and causing a <br /> net loss of precipitation. <br /> b. Urban effects <br /> Surface temperatures in urban areas are higher than those in adjacent rural surroundings. This heat island effect, <br /> coupled with increased roughness and urban structures, alters local winds and atmospheric circulation patterns <br /> leading to convergence zones which initiate clouds and precipitation under certain atmospheric conditions. <br /> Combustion of fossil fuels increases atmospheric particulates and aerosols over and downwind of major cities. <br /> This reduces air quality and visibility and also influences the local development of clouds and precipitation. <br /> Major cities with populations in excess of 1 to 2 million, and located in continental climates, influence warm- <br /> season clouds and increase precipitation by 100/o-20%,with a lesser effect on precipitation in cold seasons. <br /> Recent studies of urban areas in tropical regions have confirmed that significant modification of weather <br /> conditions also occurs in this climatic zone leading to cloud and precipitation increases. <br /> c. Atmospheric influences from industrialization <br /> Atmospheric effluents from manufacturing and power generation facilities add significantly to aerosols and <br /> trace gas constituents, increasing smog and degrading visibility. Ingestion by clouds of some emitted gases <br /> (e.g., sulfur dioxide, SO2)results in the production of acidic precipitation,which can, in sufficient <br /> concentrations, adversely affect structures, vegetation, and water quality. Large cooling lakes and cooling <br /> towers cause localized fogs, low clouds, and icing under certain weather conditions. <br /> d. Effects of large-scale transportation corridor <br /> Condensation trails from jet aircraft often persist and in areas of frequent flights sometimes spread, creating <br /> cirrus and/or cirrostratus cloud decks. These reduce insolation and can lead to lower surface temperatures. The <br /> resulting cloudiness is most frequently found along major airport corridors of the United States and Europe. The <br /> jet-induced cloud tracks can persist for many hours or even days. Traffic in major surface transportation <br /> corridors result in sizable releases of effluents (NOX's and other particulates)which affect regional visibility and <br /> degrade air quality. <br /> Top~of Document <br /> 4. Environmental and societal impacts of weather modification <br /> The impacts of weather modification on society can be far reaching.Therefore,the ecological,hydrological, <br /> socioeconomic, and legal ramifications of such activities must be considered and assessed. The complexity of <br /> the effects of altered weather have been found to lead, in most cases,to both benefits and problems in various <br /> societal sectors and environmental areas. Wise use of planned weather modification should recognize this <br /> varying distribution of effects and plan to assess the impacts in the design, operation, and evaluation of field <br /> projects. There may need to be compensation for those affected negatively and liabilities must be assessed and <br /> 5 <br />