Urban expansion, pollution growth, and development of major industrial activities in metropolitan areas impacted local climates of major cities. Transforming big cities into the heat islands is one of the most important results of micro-climate changes. In this research, the variation of precipitation is one of the most important climate factors, which was reviewed in order to study micro-climate changes. The city of Mashhad was selected for this research, as metropolitan area. The study performed by comparing the precipitation data of this city with the neighboring regions, which classified at the same climate categories. According to the effective role of rainfall in the urban weather modification and decreasing of pollutions, the rainfall variation will be more important and sensitive. The results of this research show that the rainfall variation follows the change of temperature trend. A significant correlation between temperature and precipitation changes is shown the effect of heat island on urban climate parameters. The urban heat island phenomenon increases the hot season rainfalls when we have decreasing effects on the cold season.

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