Assessing the hydrological drought of Zayande Rood Basin

Increased or decreased rainfall compared to long-term average conditions, caused two phenomena such as floods and droughts. Drought is one of the climatic events that exhibit different forms in the vast expanse of Iran and influence natural life of habitants. Drought, rising temperatures and evapotranspiration, increased consumption patterns and poor management are the fundamental elements of a water crisis.ZayandeRood river because of these reasons is faced with severe economic challenges, social and management of water resources. In this paper, the surface water supply index (SWSI) was investigated catchment hydrological drought. The results showed that the years 1377 and 1378 are the most arid years in the basin that the amounts of SWSI are -2.52 and -2.55. The most humid year is 1371 and the amount of SWSI is 2.88 the frequency of the SWSI was demonstrated that during the period, with 43% of the basin has the highest frequency in normal conditions and after it been poor drought which has a frequency of 22%. Calculations have shown that in 31% of cases, the severity of drought conditions in the area have been different.The findings indicate that the climatic drought is the vital effective factor in the Zayande Rood Basin’s water crisis with high intensity and stability in relation to its past.
According to SWSI, in a period of 23 years there exists drought state for 7 years (31%). Normal state for 10 years (43%) and humid state (26%) for 6 years. The lowest SWSI volume was in the year 1999 at -2.55 indicating the most intense hydrologic drought and 1992 with 2.88 as the most humid year in the study region.Despite other factors like water-consumption pattern, population growth, industrial use and water transfer to other regions the causation of drought is due to the climate and hydrologic droughts, the natural phenomenon. Drawing policies based on appropriate scientific water management knowledge accompanied with risk management indexes the damage level on this Basin can be reduced.