Computation of monthly runoff coefficients for Istanbul (Turkey)

Water demand for Istanbul is supplied both by impounded reservoirs located within its provincial boundaries and by water transfer from Western and Eastern regions in peripheral areas, located in South-West Black Sea region. The runoff coefficient defined as the ratio of the streamflow to the precipitation, plays a key role in the calculation of the surface water yield of water catchment areas. In this paper, we present the computation of monthly runoff coefficients for an accurate estimation of the yield of the catchment areas. We obtain statistical parameters for monthly temperatures and precipitation, based on 105-year data recorded at Istanbul Kandilli Observatory, modeled as Gaussian and Rayleigh distributed random variables, respectively. We run simulations to predict temperatures and precipitation over a horizon extending to 2100. We apply Turc’s formula and Thornthwaite method to obtain monthly runoff coefficients based on long-term data. The results are compared and discussed with the findings of previous researches