Abstract
Predicting of inflow discharge to reservoir dams is very important in achieving the purposes of reservoirs water planning. Due to climate change and human activities in the upstream of basins in recent years, the time series of discharge data has generally had downward trend. Therefore, estimating of the discharge in different statistical periods (long-term, medium-term and short-term) and analyzing it in the selection of project purposes has undeniable importance. In this study, the estimate of inflow discharge in 4 dams located in East Azerbaijan province (northwest of Iran) in different statistical periods was performed, and the effect of selecting each statistical period in the dams water resources planning was analyzed. The results showed that depending on the conditions of each basin, the selection of the appropriate discharge period will be different. But in general, choosing a short period of 15-20 years is appropriate and effective in achieving the goals of the project.