The Simulation of Discharge in Upper Helmand Basin of Afghanistan Using Multi-objective Optimization and FLEX Conceptual Model

Hirmand River is the main drainage system in the southern part of Afghanistan and has a significant impact on the socio-economic life of Sistan region. The assessment of water potential of Hirmand River is essential for long term period, which requires the use of rainfall-runoff model. The present study focuses on simulating the daily discharge of the upper Helmand basin of Afghanistan using the conceptual model FLEX in combination with multi-objective optimization, which has not been considered in previous studies. At first, the discharge was evaluated integrally by lumped model considering one objection function. Then it was simulated using semi-distributed model by adding the logarithm of the flow to the objection function. The results of this study indicates that the model is efficient in the semi-distributed mode by using two objection functions for calibration of parameters. The coefficients of NS, NS-log in the calibration and validation period were estimated to be 0.86, 0.92, 0.76 and 0.81, respectively. Pareto front analysis gave the best optimum set for each parameter used in model simulation. The model gives satisfactory results based on monthly calibration and can be used to investigate the drought and climate change research of studied basin.