Abstract

Potential effects of urban areas on rainfall patterns have been increasingly studied, debated and recorded in the archived literature since 1921, when Horton observed rainstorm development over two cities, Albany, New York, and Providence, Rhode Island, which he attributed to the presence of the urban areas. Temperature is the most commonly studied climate variable influenced by urbanization, but other components of the water cycle studied include rainfall, infiltration, runoff, and evaporation. Generally scientists agree that urbanization affects spatial and temporal (diurnal) temperature patterns in cities. The science behind the effect is fairly well defined. However, urbanization effects on rainfall are not as well defined and consensus has not been reached among scientists regarding the existence and importance of the effect and the contributing factors.

Although numerous studies of urban impacts on rainfall have been performed including comprehensive field monitoring campaigns, sophisticated numerical modeling studies, and innovative data analyses, certainty has not been achieved. Defensible certainty is difficult to achieve because field experiments are uncontrolled, data analysis relies on limited data resources, and modeling and computational limitations have prevented comprehensive analysis of all influencing factors. As advances in technology and the availability of large volumes of rainfall data progress, this obstacle diminishes. Computer programs are becoming increasingly capable of handling massive amounts of data input, facilitating the use of high-resolution data necessary to accurately depict spatial rainfall patterns and urban land surfaces.

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