Analyzing the impacts of climate change on the river discharge regime is very important to doing successful water management and further adaptions strategies. The aim of this study is to analysis impact of climate change on the river discharge regime over Iran. To this end, daily flows from 124 hydrometric stations during 1982-2013 were obtained from the Iranian Water Resources Management. Stream flow regime classification carried out based on six hydrological indices that included a number of flow characteristics and represent the flow regimes as ephemeral, intermittent, and perennial. To understanding characteristics of the flow regimes, Flow Duration Curves (hereafter FDC) for different stream regimes analyzed. To assess the impact of climate change on river discharge regime, the area average annual anomalies of the precipitation and temperature time series analyzed. The result of applying the Hierarchical Ward clustering method on six hydrological indices shows that the124 hydrometric stations can classified into three clusters including ephemeral, intermittent, and perennial stream regimes. The spatial distribution of the stream regimes types show that most of hydrometric stations over Iran fall in the Intermittent followed by the Ephemeral groups. The Perennial streams located on the southwestern part of Caspian Sea in the north and southwestern part of country where precipitation is high. FDC for different stream regimes indicated that the streams in the ephemeral flow regime shows a sharp curved shape indicating the flashiness characteristics of the streams, while the streams in the ephemeral flow regime shows a less steep curve, implying non-flashy streams. The streams in the ephemeral flow regime show more variability than the streams in the perennial flow regimes. The area average anomalies of precipitation, temperature, and streamflow in the time period of 1979-2013, have calculated. Based on the studied period can be divided into two different periods: a wet and cold period (1979-1998) and a dry and hot period (1999-2013).
