A Comparative Analysis of Precipitation and Drought Trends in Caspian's Basin

In order to evaluate climatic drought trend in 23 hydrological basins of Caspian Sea, monthly precipitation maps of the basin for 588 months (1951-1999) have been prepared. Based on these maps Standard Precipitation Index has been calculated and considered as drought indicator for the basins.Standard Precipitation Index of 23 hydrological basins of Caspian Sea has been analyzed using cluster analysis. According to agglomerative hierarchical clustering analysis there are four drought regions in Caspian's basin. A nonparametric Mann-Kendal trend analysis applied to precipitation series and SPI separately. For precipitation time series basins showed that Jan., May, and Dec. havent significant trends. At the same time 5 basins in February, July have significant positive trend and 11basins in March and September have significant negative trends.A nonparametric Mann-Kendal trend analysis for SPI showed that May, none basins havent significant trends. The highest significant trend showed in July and August.