Variability in Time and Space: Flow Regimes and Seasonality Indices in the Mountainous Rivers of Northern Iran

ABSTRACT This research investigates the spatiotemporal changes in river flow regime seasonality in northern Iran and evaluates its spatiotemporal changes. The Seasonality Index (SI) was used to evaluate the level of seasonality present in monthly river flow data, and the spatial pattern and variability of their characteristics were investigated. The northeastern parts of the study area have the highest CV and SI values, with heavy rainfall affecting water yield values and snowmelt‐fed rivers in some areas. The SI values ranged from 0 to 0.77, with the highest values observed in the northeastern parts of the region. The Baladeh, Razan, and Ploor stations had a “seasonal” flow regime influenced by the timing of snow melting from the Alborz Mountain foothills. The SI‐k map matches the SI index, showing higher annual water yield seasonality in the northeast of Mazandaran. The study concludes that the spatiotemporal changes of the SI in Mazandaran province demonstrate higher water yield values in the central region, with the northeastern area having high CV and SI values. The study demonstrates the importance of understanding the seasonality of hydrological characteristics of the rivers for water management and disaster risk reduction in the region. The findings suggest that water yield patterns are changing in the region and that these may impact water availability, flood risk management, and ecosystem services.