Application of PCI Index in the Annual and Seasonal Rainfall Pattern Investigation and Trend Analysis of Iran Duration the Recent Half Century

Evaluation of the rainfall phenomenon is important as the most effective meteorological factors that influence the access to the water resources directly. In this research precipitation concentration index (PCI) calculated using of monthly precipitation time series of 34 synoptic stations in the recent half century (1961-2010) and their trends in two annual and seasonal scales investigated. The results of the zoning the mentioned index in annual scale showed that concentration of the precipitation in two 25 years time reach followed from the same pattern. Also results of PCI index showed that rainfall was scattered irregular in the center and southern regions of Iran in the Kerman، Bandar Abbas، Yazd، Zahedan، Shahrekord، Birjand، Bushehr، Ahwaz and Isfahan also in none of the mentioned stations uniform concentration (PCI <10) were not observed in the annual time scale. Results of winter trend investigation of PCI index in the period of 1961-2010 showed that non significant upward and downward trend occurred for the number of sixteen and fifteen stations respectively and in the Dezful، Saghez and Hamedan stations significant decreasing trend observed. Also in the spring season، PCI index results showed significant increasing in the PCI trend for two Kerman and Ramsar stations which means that scattering rainfall was irregular significantly in two mentioned stations. In summer، the Gorgan station showed high irregularity as the PCI index and in autumn، the Tabriz and Zahedan stations showed significant increasing trend while decreasing trend detected for Bablosar station. In annual scale about 50 percentages followed increasing of PCI index values.