Estimation of Water Balance Components and Analysis of Variations Using Modeling and Remote Sensing Approaches (Hashtgerd Study Area, Alborz Province)

In management and planning of water resources, hydrological models are suitable tool that can be very effective in simulating hydrological processes such as water balance. Distributed hydrological models simulate each of the water balance parameters by discretization and solving equations in each cell. In the present study, the WetSpass-M distributed model is used to estimate and evaluate the components of the water balance in Hashtgerd study area in Alborz province. The model was implemented in monthly basis and for a 20 year period. In order to calibrate and validate the model, first the monthly flow data of the hydrometric station were used as observational data. The remote sensing approach (SEBAL algorithm) was applied to re-estimate evapotranspiration. Then, the results of the two approaches were evaluated and compared. According to the model results in the Hashtgerd study area, the mean annual values of evapotranspiration and groundwater recharge were estimated to be 347.3 and 272.6 MCM, respectively. Furthermore, the mean annual values of evapotranspiration for plains and mountains were respectively 241 and 106.3 MCM. The mean annual recharge rate in the plains was equal to 197 MCM, while it was estimated to be 75.6 MCM for mountains. The variations analysis of model outputs was performed based on the standard deviation for the water balance parameters in plains and mountains. The results showed that the most variations during the simulation period were observed respectively in the irrigation component, evapotranspiration, recharge, and rainfall.