Investigation of PCI Drought Index and Its Trend Over Iran in The Recent Half Century

Precipitation is one of most the important parameters of climate that affects water resources directly. In this research changes of precipitation pattern in Iran investigated by means of PCI index. In this order 25 synoptic stations of Iran during two periods of 1961-1986 and 1986-2010 used to calculate PCI index and then significance of this index evaluated by t-test method. Results of mapping this index over Iran showed that precipitation changes had the same pattern in the two studied periods of time. Also results indicated that PCI index was high in the central part of Iran and in the low-precipitation provinces such as Kerman, Hormozgan, Yazd, Zahedan, Shahrekord, Birjand, Booshehr, Ahwaz and Isfahan. These stations according to the Oliver (1980) classification showed high irregular precipitation pattern. According to the results most parts of northwest followed irregular precipitation pattern. Two stations of Rasht and Gorgan had intermediate PCI index values and Zanjan and Tabriz stations had almost intermediate PCI index values. In none of stations uniform precipitation pattern (PCI