Assessment of the flow regime of the Simineh River using the Indicators of Hydrologic Alteration (IHA) approach

Rivers play a crucial role as vital water resources in meeting drinking water, agricultural, and industrial needs, as well as in maintaining aquatic ecosystems. The flow regime of rivers is influenced by both natural and human factors. Human activities such as dam construction, river diversion, and land use changes have significantly impacted river flow regimes. Rivers provide essential needs for all vital activities and ecological processes. The riverbed shape, flow dynamics, and erosion-sedimentation processes are linked to the river's natural structure and function. Maintaining features such as flow rates and seasonal variations is crucial for river ecosystem sustainability. Ecologists consider river flow and its variability as key factors influencing many fundamental ecological processes in river ecosystems. However, in the context of climate change and increased human activities, the hydrological characteristics of natural rivers have undergone significant changes. Dams and reservoirs, and their impact on the diversion and regulation of flow upstream and downstream, are the main factors contributing to the loss of river continuity. In this study, the changes in the flow regime of the Simineh River at the Dashband hydrometric station in the Lake Urmia basin were analyzed using the Indicators of Hydrologic Alteration (IHA) model, and the values and variations of 33 hydrological parameters were calculated. The results showed that most monthly flow rates exhibited a significant decreasing trend. Specifically, the flows in October, November, February, and March showed a sharp decline with a negative slope and a 95% significance level over the statistical period. Although flows in June and July had a positive slope, the trend was not statistically significant. The minimum flow indices over 1-, 3-, 7-, 30-, and 90-day periods showed a significant downward trend (p < 0.01), indicating a reduction in baseflow. Maximum flows also showed a decreasing trend, although it was not statistically significant. The number of zero-flow days (slope 3.4) and the duration of low pulse events (slope 2.82) exhibited a significant increasing trend (p < 0.01), reflecting intensified hydrological drought conditions. The timing of maximum flow occurrence was delayed (slope 0.7, p = 0.005), while the changes in the timing of minimum flows were not significant. The baseflow index showed a slight decline (slope 0.001) but was not statistically significant (p = 0.25). Additionally, both the rise and fall rates of flow increased significantly (slopes 0.021 and 0.005, respectively), indicating greater flow instability. The number of flow reversals decreased significantly (slope 1.1, p = 0.01), possibly due to a reduction in the frequency of sudden flood events. The findings of this study, highlighting changes in the natural flow regime of the Simineh River, demonstrate that hydrologic alteration indices can serve as effective tools in water resource management; analyzing changes in each index (such as baseflow reduction, increase in zero-flow days, or shift in peak flow timing) provides important management applications in planning for drinking water supply, agriculture, drought control, and aquatic ecosystem protection across different dimensions of water management.

The trend of changes in certain indicators shows an increase in hydrological fluctuations and instability in the river's flow regime, which may be attributed to the impacts of climate change or human activities such as water diversion, excessive withdrawals, and potential land-use changes. These results indicate that the flow regime of the Simineh River at the Dashband station has undergone significant changes in recent years, which could pose a serious threat to aquatic ecosystems and water supply in the future. The findings of this study show that the river flow in the Dashband-Bukan basin, particularly in the spring months, has significantly decreased, the number of dry days and the duration of drought periods have increased, the timing of maximum flow events has been delayed, and flow variability has increased. Additionally, the base flow of the river has consistently decreased. To complement these findings, it is suggested that the relationship between river flow changes and climatic parameters be investigated, the effects of human activities and land-use changes on the watershed’s water regime be analyzed, and flow prediction models be developed considering various climate change scenarios. From a management perspective, it is necessary to review the water allocation pattern, prioritize environmental needs, and focus on integrated management of surface and groundwater resources. Overall, water resource management policies should be updated considering climate change, and adaptation strategies should be implemented with the involvement of local communities and stakeholders to ensure greater effectiveness. Therefore, the need for water resource management and the adoption of optimal policies to protect natural and sustainable flows in this basin is essential.