Hydro geo-sphere integrated hydrologic model in modeling of wide basins

Simulation of large basins (over 1000 km²) can have a significant impact on the planning of large-scale water resources management. However, due to the increasing volume of calculations and the increasing heterogeneity of the different parts of these basins, the simulation of these basins has always faced challenges. Also, in areas with severe withdrawal of water resources, the importance of simulating and having the ability to predict future changes in the area is twofold, while these severe withdrawals lead to more complicated issues and more difficulty in simulations. The aim of this study is to evaluate ability of hydro geo-sphere fully integrated hydrologic model in simulating a large basin area (Hamadan-Bahar) with a total area of 2456 km² and in severe withdrawal from groundwater resources. In this study, fully integrated surface/subsurface flow modeling was performed using hydro geo-sphere model. Simultaneous solving of surface and groundwater flow equations in this model and also the calculation of actual evapotranspiration as a function of soil moisture in each unit of evaporation zone improves simulation of interdependent processes such as aquifer drainage and feeding, which is one of the most difficult issues in the modeling. To obtain the initial conditions, the model was performed in steady-state mode using 20-year average of rainfall data and withdrawal from the aquifer. Then, to implement the model in a non-steady state and evaluate its performance in daily stresses, the model was performed during the period of 1992–2005 and parameters were calibrated. Validation phase was performed during the period of 2006–2010, which indicated the acceptable ability of this model in hydrologic simulation of the study area.