عنوان مقاله [English]
In the midst of extreme events, the droughts are gradually taking place and over time, they leave behind their effects. Among the drought monitoring methods, Nalbanti proposed SDI method based on the analysis of drought characteristics based on the quantity of cumulative river volumes.This method has been used to analyze the drought characteristics of many countries such as the United States, India, Iran, Iraq and Greece.
Materials and methods
The average of annual rainfall mean in Kermanshah province is 437 that In recent years, due to climate changes and temperature increase, rainfall during the wet season has increased and it decreased during the dry season.The difference in river volumes between the wet and dry seasons has led to the occurrence of drought.The purpose of this study is to investigate the continuity and severity of hydrological droughts using River FlowDrought Index (SDI) based on periods of 3, 6, 12, 18 and 24 months in this province.In this researchwere used statistics and information about the hydrometric station of water resources management in Iran.To achieve this goalwas used daily discharge data from 10 hydrometric stations for a period of 31 years (1981-2011).The result of the river flow index showed that at the stations of Totashi, Shah gozar, Arangharb, Doab, Plochehr, Khers Abad, DuabMerk and Ghorbaghestan, wet years began in 1363 and continued until 1998.And the beginning of the drought at the stations of Totashi, Arangharb, Plochehr, Khars Abad, DuabMerk and Ghorbaghistan from 1998 and continued to the recent years (2011).
Results and discussion
Comparison of Pearsolaiman and Shahgozar stations in terms of drought status indicates that drought status of Shah gozar is milder than Pearsolaimanstation And in general, it has no severe drought and At both stations is seen in years wet.In other words, the drought condition is normal and the drought values are not considered based on SDI above -1.562, and the situation has been similar and close to the two stations. By counting and comparing the number, severity and frequency of occurring droughts at Shah gozarand Pearsolaimanstations based on the SDI index, it has been observed that in the years 2004-2011 there has been a continuous period of drought for the Shahgozarand at the station Pearsolaimanis a continuous five-year drought period from 2007 to 2011.According to the results of this index, all hydrometric stations of the studied area have been at least once witnessto severe drought. Also , almost all of Kermanshah province is talented to drought risk.Shahgozar and Duab watersheds were more susceptible to drought and more exposed to drought.Since the statistical period of 1998-2003, the area has been affected by drought, which is consistent with the flow values obtained from these years.In other words, in these years, the region was more affected by moderate to mild droughts.
The hydrological drought trend has increased over time in different regions of the province, so that in 1989 most of the area was normal in terms of drought, but in 2011, a large part of the province was moderated by drought.The drought trend is rising in the selectedstatistical range in this region.