Heat island and urbanization effects of Tehran have been studied using time series of long term (about 40 years) weather records. This investigation shows a significant increase in minimum temperatures compared with maximum temperatures. The greatest trend for the mean temperature has occurred in November. Comparisons of time series of temperature for Tehran and Varamin in this period show that the rate of annual minimum temperature increases in Tehran was four times lager than that of Varamin(S.Tehran). Although a decrease rate of maximum temperature seems to be observed in both stations. The highest trend of mean monthly minimum temperature in Tehran and Varamin were 4.64°C and 2.12°C respectively, which were occurred in November. This indicates that the artificial and anthropogenic increases of temperature leading to urban heat island in Tehran have been significant in this period. This study also indicates that drainage of cold air from northern mountains over Tehran (Mehrabad) has also been weakened due to the increase in built-up area. The wind decreasing trend intensifies urban heat island effect.
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