Effect of ENSO Phenomenon on Variability of Surface Water Resources in Hamedan Province

Investigation of the factors affecting streamflow is of great importance in water resources studies. In recent years, the impacts of large-scale climatic phenomena on river discharges and study of their variations via ENSO phenomenon have been noticed by many researchers. In this study, the influence of ENSO events on stream flow rates of 14 hydrometric stations were studied in Hamadan region using the indices of TNI and MEI. The results showed that the amounts of streamflows in the all hydrometric stations had different reactions to the ENSO phenomenon. The obtained results on the bases of the TNI and MEI indices, confirmed the variability of the streamflows from the Enso phenomenon in 11 and 10 months of the studied years, respectively. Investigation of density or percentage of the occurrence of the La Nina phases of the ENSO’s indices in the studied area showed that in 64.12 and 43.89 percents of the cases, the La Nina phase of TNI and MEI indices were dominant, respectively. Also fitting a regression model to streamflow discharges in the hydrometric stations and ENSO indices showed that about 75 percent of the dicharge variations could be expressed by the TNI index in the study region, while the MEI index could express about 51 percent of these variations. In general, it can be concluded that using the TNI index to express the monthly streamflow variations in Hamedan province is more suitable than the MEI index.