Sends any data from the Hydro unit (stored in Hydro_data) to the IO unit, through the IO_setScalar interface, for checkpointing. Can retrieve the data upon restart in Hydro_init through the IO_getScalar interface. This is the API stub implementation.
IO_setScalar, which puts a scalar into the IO unit so it can make it into a checkpoint.
IO_updateScalars, which calls this function to let Hydro know it's time to checkpoint.
Here's what an implementation of this function might do: USE IO_interface, ONLY : IO_setScalar call IO_setScalar("time", simTime)