Investigating Changes of Seasonal Precipitation Concentration of Iran in Recent Half-Century

In different regions of the world, numerous studies have been conducted on climate change. The results of those studies show the changes in climatic factors, especially in precipitation and temperature. Investigation of the precipitation phenomenon as one of the most important meteorological factors has a special importance in the availability of the water resources. In this study, using the precipitation concentration index in a seasonal scale, the variations of this important phenomenon in Iran, were investigated. Using the monthly rainfall time series data of 25 synoptic stations in Iran during 1961-2010, the precipitation concentration index values were extracted in the seasonal scale. The data were evaluated in two sub-intervals of 25 years. The significance of the mentioned index in two sub-intervals was analyzed using t-test. The seasonal trend of the precipitation time series and the precipitation concentration seasonal index were investigated using the Mann – Kendall test. The zonation results of precipitation concentration index showed that the distribution of the precipitation in the both sub-intervals obeyed the same pattern. The mentioned index in the south and central provinces of Iran having the low precipitation such as Kerman, Yazd, Sistan and Baluchistan had high values. In general, the results showed that according to the mentioned index, Iran's territory could be divided into three parts (from the view point of precipitation concentration pattern): the North area and Caspian Sea shores as the first part having the moderate density and pattern of rainfall, central as the second part having the irregular pattern of precipitation and the Oman Sea and the Persian Gulf margins having a highly irregular pattern of rainfall.