Studying the climatic drought in rice cultivation period in different parts of Guilan province using SPI index

The basis of monitoring drought in every region is reviewing the specifications of the occurred drought. In recent years, cutting the distributaries of Sepidrood river due to construction of several dams on the upstream has increased the effect of rainfalls in the province on sustainability of rice fields of Guilan province. This study is aimed at investigating the climate-related drought and studying the characteristics of this phenomenon in Guilan province and the difference between the severities of climate-related drought in different price fields of the region over a 35-year period. For this purpose, standardized precipitation index (SPI) was used. The precipitation data of thirty rain-gauge stations regarding the standardized precipitation in two periods, crop season and whole year periods, related to four regions including the central district of Guilan, east of Guilan, Foumanat, and west of Guilan were investigated. The results showed that a great area of the province has been involved in drought in the crop period in 2013, 2008, 1999, and 2014. The highest severity of drought in the crop period drought was related to Foumanat region during the water year 2007-2008 with a SPI value of -2.06. The evaluated value of this index in the crop period relative to its value during the whole year showed that in all of the four regions, severity of the drought in the crop period was more than its severity in the year period, and the frequency of drought occurrence in the crop period was over two times more than the year period. Also, calculation of SPI index in the crop period shows a more accurate performance than the 12-month period during which a significant part of the precipitation potential is wasted and lost from the agricultural system of the Guilan province.