عنوان مقاله [English]
Rainfall change as a result of climate change is one of the important issues of recent decades. Climate change can be represented as changes in the inter-annual precipitation distribution and seasonality. Furthermore, the seasonality changes and the transposition of the seasonal precipitation are very important for agricultural and hydrological domains decision makings. In this paper, in order to quantitatively investigat the inter-annual distribution of precipitation, at first the seasonality index and the normalized seasonal precipitation anomaly are calculated. For this purpose the monthly rainfall of 33 synoptic stations are used over Iran. The spatial distribution of the seasonality index average and also the year occurrence of maximum and minimum index for each station are identified. Then the significant trends of seasonality indices and also the normalized seasonal precipitation anomaly are examined using Mann-Kendall test for the period 1977-2006.The results show the minimum seasonality index for Gorgan station in the south east of the Caspian Sea, and the maximum seasonality index for Bandarabas station in the south of the country (the coast of the Persian Gulf). The precipitation tends to be concentrated in few months of the year in most stations for the study period (only three stations show significant trends). The maximum seasonality index is observed after 1990 in most stations. However, the trends of seasonal rainfall anomalies for all four seasons in the northwest parts of Iran are negative, but in the central and western regions changes in anomaly trends are positive. This means that seasonal rainfall year to year variations are reduced in the northwest of the country. Highest number of significant trends is observed in winter precipitation.