Evaluation of drought selected stations by Standardized Precipitation Index (SPI) on Wetland Gandoman

Drought is a natural reduction in the occurrence of continuous rainfall in the period of time that usually lasts for a season or more,and its effects impose irreparable damages to the human population,animals,plants and the environment every year in different climates. the aim of this study was to evaluate and compare the impact of meteorological drought by standardized precipitation index [spi] on different time scales of the selected stations on wetlands gandoman. in order to,the intensity and frequency of the drought of spi3,spi6 and spi9 by monthly precipitation data over a 19 years statistical period from 1994 to 2012 were determined. and zoning maps was drawn based on the spi%. graphical method was used to analysis of the trend of changes the spi12 and annual discharge average data. the results showed that all stations have been faced with the extremely and or very severe drought by the spi3 in 1999. this situation occurred by spi6 and spi9 in 2008. spi3,spi6 and spi9 showed severe wet at 2006 for all stations. the zoning maps of spi% showed that wetland gandoman up to 29-35.5% by spi3%,25-31.5% by spi6% and 26-29% by spi9% has been affected by drought. maps of different scales of spi% caused the different directions in expanding drought. trend changes was alternating by drought (spi12) and the average annual discharge data and increasing the drought was accompanied by the reduction in discharge and vice versa.