This global feature is automatically added when the Account for gravity in liquid velocity check box is selected at the interface level in the Physical Model section. It defines the gravity forces from the Acceleration of gravity value, g, for the computation of the liquid water flux, gl:

See Hygroscopic Porous Medium for details about the other terms in the equation above.

The Acceleration of gravity (SI unit m/s) should be set to a global quantity. It is set by default to -gconstez in 2D axisymmetric and 3D models, and -gconstey in 2D models.