برخي مشخصه هاي آماري بارندگي تهران

Precipitation is one of the most important climate elements. The important characteristics for arid and semi-arid regions are low and high fluctuation of Precipitation, and in some years it may exceed annual average. Since there is no control over climate elements, it is very important to know those changes. In this case study, we analyze the precipitation data in Tehran during the period of 1951-1988. Tehran is one of the relatively arid regions in Iran. Results of the research showed that the average precipitation during the above period is 230 mm. The Standard Deviation (SD) is 73 mm and Coefficient of Variation (CV) is 33 percent. Distribution of seasonal precipitation is 20, 2, 30, and 47 percents for Spring, Summer, Fall and Winter respectively. Precipitation analysis in recent 5 years showed that the occurrence of precipitation is in fifth decile. Furthermore this study showed that the return period is 15 years and its trend is toward drought.