Disaggregating the Effects of Climatic Variability and Dam Construction on River Flow Regime

The objective of this study is to investigate the changes in the river flow regime under the influence of dam construction and climatic variability and disaggregate their individual effects. Daily discharge, temperature, and precipitation data were collected from Qaranqo River basin in East Azerbaijan (Iran) for the period of 1971–2017. To disaggregate the effects of climatic variability and dam construction, daily river discharge data after dam construction were simulated using an Artificial Neural Network (ANN). Then, with the use of Indicators of Hydrologic Alteration (IHA) and annual indexes, river flow regime changes were examined. Results showed that monthly flows in all months except for July, August, and September, decreased. Also, annual maximum flows (except for a maximum of 1 day) decreased and minimum flows (except for a minimum of 1 day) increased. The Julian dates of minimum and maximum flows had also preceded, in which both dam construction and climatic variability were influential. Both dam construction and climatic variability were equally effective for monthly flows, extreme flows, and Julian dates of extreme flows. However, dam construction played a greater role in the changes of high and low pulses, and fall and rise of flow hydrograph. The two indexes of relative and absolute ranges of variation of intra-annual parameters had decreased, while the non-uniformity coefficient, concentration degree, complete accommodation coefficient, and Richards-Baker index had increased, which were mainly affected by climatic variability. In the Environmental Flow Components (EFC) in the group of low monthly flows in most months, there was little difference between observed data and simulated data, which indicated the role of climatic variability in the river flow regime. By contrast, there was a significant difference in peak, duration, and time of large and small floods, which indicated the role of the dam construction in these components. Climate variability had the most role in changes of monthly low flows, extreme low flows, and high flows of river flow regime, while in small and large floods, the role of dam construction was significant. It can be concluded that the effect of climatic variability on flow regime in the Qaranqo River basin, was greater than the effect of dam construction.