Different time-stepping schemes are used for horizontal scalar advection when wetting and drying occur (vertical
advection always uses the method). To guarantee consistency
with continuity, the method must be used for scalar advection. This is formally first-order
accurate in time, so results are more accurate when second-order Adams-Bashforth is used if there
is no wetting and drying. Therefore, the wetdry Boolean is set according to:
(0): No wetting and drying, employ AB2 for horizontal scalar advection
(1): Wetting and drying: employ -method for horizontal scalar advection.
Depending on the stratification at the surface and the grid size it is often desirable to employ wetdry = 1 so as to ensure consistency with continuity and avoid spurious oscillations in the temperature and salinity fields.