Dynamical Time Step Adaptation
MOHID Land uses an adaptive time-stepping method in its main hydrodynamic cycle. Within an iterative cycle, if the water volume — of reach or overland flow or porous media — varies more than a user defined percentage during two consecutive time steps, the model automatically decreases the time step. Thereafter the model recalculates the current solution with a smaller time step for the affected process (reach or overland flow or porous media). This process is repeated until the volume variation is less than the user defined value mentioned above. The time step dynamically increases again when the model verifies that flow is “stable”. For example within the module "Drainage Network" the time step may be reduced to very short intervals during flush events. This procedure avoids the occurrence of negative volumes and optimizes the time it takes to make a certain simulation, without compromising model stability. Time steps of the processes — computed in the different sub-models — can be chosen differently, adding more to the optimization of the computational cost.
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