Drought is one of the most destructive and important climate phenomena, whose impact is usually more important on a regional scale. The importance of this phenomenon in the Karkheh basin is more obvious due to its size and important role in providing the country's water resources. In this research, the aim of eva‎luating hydrological drought using standard flow index (SSI) in the time scale of one month by choosing the best fitted statistical distribution based on goodness of fit tests and linear moments for each station, regional analysis of intensity, duration and The frequency of hydrological drought in Karkheh basin is 30 years (1365-1395). For this purpose, the monthly discharge data of the hydrometric stations obtained from the site of the Ministry of Energy were used and the results showed that severe drought and severe drought rarely occurred in the region, but the mild drought accounted for the largest share and this An alarm for proper management in order to prevent the harmful damages of drought is that due to factors such as land use change, dam construction, climate change, excessive water harvesting the region has experienced drought and according to the results of the research This situation has taken a large share in the years 1387 to 1394. In this study, the drought threshold limit of -0.5 is considered, and the intensity and duration of the two important features of drought are used to predict future droughts, and it is worth noting that why the phenomenon of drought occurs every year and continuously. to give and we analyzed the duration of this phenomenon as an occurrence. Next, after clustering the stations in SPSS software, the area was divided into two groups, and after checking the homogeneous areas using the software provided by Hosking, three awkward stations were removed from the 26 stations of the first group, and H1 was smaller From 1.5 , this group reached homogeneity, but the second group was awkward with 6 stations without stations, and at the smaller H1 level of 1.5, its homogeneity was further confirmed after the regional analysis, the appropriate regional distribution for the intensity and duration of both groups. Pearson type three was selected. Then regional growth curves were drawn using regional distribution parameters. These curves indicated that the first region, which includes most of the northern part of the basin, has a shorter period of drought. Finally, due to the non-correlation of the characteristics of the basin with the flood index of the region, which was concluded from the correlation matrix, a suitable regional model was not obtained. It is worth mentioning that in this research, unlike previous studies, which usually used the gamma distribution, the best distribution was selected after fitting the statistical distributions.

سعيد سلطاني كوپائي , رضا مدرس

وحيد چيت ساز

سعيد پورمنافي , عليرضا گوهري