شناسايي تحليل روند خشكسالي هاي اقليمي زيرحوضه هاي زاينده رود در نيم سده گذشته

Trend Analysis of Climatic Drought in Zayandehrood Sub Basins during the Last Half Century

In order to evaluate the drought trend in Zayandehrood sub basins monthly precipitation maps of the Zayandehrood basin for 588 months (1951-1999) have been prepared using kriging method. Based on these maps Standard Precipitation Index has been calculated and considered as drought indicator for the sub basins. A nonparametric Mann-Kendal trend analysis applied to precipitation series and SPI series separately. For precipitation time series none of the basins showed significant negative trends. At the same time in February, March, May, and June significant positive trend detected. The March Precipitation in All sub basins of Zayandehrood has significant positive trends. A nonparametric Mann-Kendal trend analysis for SPI showed that in Jun, April, May, July, August, October, November and December none of the basins showed significant trends. The highest significant trend appeared in March, February and June. All sub basins have significant trend in March.