fractRunOff = 1. _d 0
fractRunOff = land_fractRunOff
& + fractRunOff*grdWexcess*land_rhoLiqW
& + (1. _d 0-fractRunOff)*grdWexcess
& + fractRunOff*grdWexcess*enthalpGrdW
& + (1. _d 0-fractRunOff)*grdWexcess*enthalpGrdW
_RL groundWnp1, grdWexcess, fractRunOff