Development of a Daily Rainfall-Runoff Model to Simulate the Bukan Reservoir Inflow and Quantify the Effects of Severe Historical Drought Using WEAP Model and MultiObjective Calibration

Urmia Lake has faced a water shortage crisis and a sharp decline in water level due to decreasing precipitation and increasing water consumption in the agricultural sector. This study aims to develop a hydrological model to simulate the daily inflow of Bukan reservoir and simulate the water balance components for the upstream sub-basins of this reservoir through a new approach. In this study, two separate storages are considered for daily simulation of snow and root zone soil moisture, and multi-objective calibration (MOPSO) is applied to simultaneously maximize the simulation accuracy of observed river discharge and logarithm of river discharge. The results showed a relatively little trade-off between maximizing the two objective functions to estimate the optimal value of the calibration parameters. In other words, there is no significant error in the model that simultaneously prevents improving both objective functions. Results showed that the average Nash-Sutcliffe criterion for simulation of river discharge and the logarithm of river discharge were respectively 0.43 and 0.63 in the calibration and 0.54 and 0.57 in the validation step. Water balance modeling indicated that precipitation and inflow to the reservoir were decreased respectively by 32% and 40% in severe drought years and soil moisture and snow accumulation were reduced by 32% and 158%, respectively, compared to the long-term period. The developed model can predict the effects of climate change and climate variability on Bukan reservoir inflow and optimally allocate reservoir water to satisfy water demand.