Abstract Aims: Conversion of orchards and agricultural lands in urban areas to residential and commercial areas has made a wide range of hydrological changes in urban watersheds. The aim of this research is to provide an Urban Distributed Hydrological Balance Model (UDHBM) to investigate the urban runoff in some parts of Tehran, including Tajrish and Elahiye. Methods: To reach this goal, at first, we broke down the runoff amount of upstream mountain and urban areas from measured values. The HEC-HMS Model has been used to determine the volume of net runoff and flood produced in metropolitan areas. The annual water balance model considering rainfall, evaporation and other necessary inputs, have been made after defining the amount of flood in metropolitan areas. In the next step, a sensitivity analysis has been carried out on the main factors affecting the model to obtain a better understanding of the behavior of the model by changing these factors. Findings: Results of this sensitivity analysis showed that this model has the most sensitivity to the rain factor and soil hydraulic conductivity. The results of comparing estimated values and urban runoff observations show minimum root-mean-square error and maximum correlation coefficient of 89% with a significance level of 5%. Conclusion: This means that the UDHBM model has a good ability to calculate the runoff volume based on water balance for each land usage including residential houses and buildings, streets, parks and urban green spaces.

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