Rapid urban expansion, land use change, and climate variability have significantly influenced the hydrological behavior of many watersheds surrounding large metropolitan areas. In Tehran, several mountainous and semi urban basins are increasingly exposed to short duration intense rainfall events that can trigger flash floods. Among these basins, the Kan River basin located in western Tehran plays an important role in regional hydrology, sediment transport, and flood generation processes. Understanding the temporal variability of precipitation and the behavior of peak river discharge in this basin is therefore essential for improving flood management and water resources planning. Despite the importance of this watershed, comprehensive analyses that simultaneously examine precipitation variability, annual peak discharge trends, and flood characteristics remain limited. Accordingly, this study aims to analyze precipitation trends, evaluate annual peak discharge behavior, and investigate the characteristics of recorded flood events in the Kan River basin in order to provide a clearer understanding of the basin’s hydrological response and its implications for flood management.
In this research, long term observational data including daily and monthly precipitation records, meteorological data, annual peak discharge values, and flood event information from hydrometric and meteorological stations within the Kan River basin were used. First, temporal variations of precipitation were analyzed at both annual and seasonal scales to identify dominant rainfall patterns and interannual variability. Subsequently, the time series of annual peak discharge was evaluated to determine the behavior of extreme flow conditions. In the next step, flood events were examined through the analysis of flood hydrographs. Key hydrological indicators such as peak discharge magnitude, time to peak, flood duration, and hydrograph shape were extracted and analyzed to better understand the watershed response to rainfall events. This methodological framework enables a combined assessment of precipitation variability and hydrological response, which is particularly important for watersheds that are susceptible to flash flooding.
The results indicate that precipitation in the Kan River basin exhibits considerable interannual and intra annual variability. A significant portion of the annual precipitation occurs during the cold and transitional seasons, mainly from October to May, while summer months contribute only a small fraction of the total annual rainfall. This temporal distribution corresponds to the semi arid Mediterranean type climate that characterizes the Tehran region. The analysis of annual peak discharge and flood events also reveals that the watershed is highly responsive to intense rainfall events. In several cases, flood hydrographs demonstrate rapid increases in discharge within short periods, indicating the potential for flash flood formation. Such behavior is typical of mountainous watersheds where steep slopes and limited infiltration capacity can accelerate runoff generation.
The integrated analysis of precipitation patterns, peak discharge trends, and flood hydrograph characteristics provides a comprehensive picture of the hydrological behavior of the Kan River basin. Compared with studies that focus only on rainfall variability or discharge trends separately, this research offers a more holistic perspective on the mechanisms governing flood generation in the basin. Furthermore, the findings are consistent with previous studies conducted in the Tehran region that highlight the dominant role of cold season precipitation and extreme rainfall events in shaping regional flood regimes. By combining multiple datasets and hydrological indicators, the present study contributes to a better understanding of watershed dynamics and flood processes in semi arid mountainous environments.
The outcomes of this research can support improved flood risk management, watershed planning, and infrastructure design in the Kan River basin. Knowledge of precipitation variability and peak discharge behavior can help authorities better anticipate flood hazards and develop more effective mitigation strategies. Moreover, the methodology applied in this study may be useful for similar watersheds in other semi arid regions where hydrological responses are strongly influenced by seasonal rainfall patterns and extreme events.