diff --git a/physics/sfc_diff.f b/physics/sfc_diff.f
index e25506a09..ce8b6decb 100644
--- a/physics/sfc_diff.f
+++ b/physics/sfc_diff.f
@@ -258,6 +258,13 @@ subroutine sfc_ex_coef_run                                        &
             endif
 ! - Calculate the roughness length for heat (see eq.(1) of \cite zheng_et_al_2012 ) .
 ! mg, sfc-perts: add surface perturbations to z0max over land
+!! Following Gehne et al. (2018) \cite gehne_et_al_2018, a perturbation of the momentum
+!! roughness length (z0pert) is added using a logrithmic scaling. The spatial pattern of
+!! z0pert is drawn from a normal distribution with a standard deviation of 0.14 while is 
+!! bounded between -0.5 and 0.5. Similarly, a perturbation of the ratio between the roughness
+!! length for heat to the momentum roughness length (ztpert) is added. The spatial pattern
+!! of ztpert is drawn from a normal distribution with a standard deviation of 0.08.
+
             if ( islimsk(i) == 1 .and. z0pert(i) /= 0.0 ) then
               z0max = z0max * (10.**z0pert(i))
             endif
diff --git a/physics/sfc_drv.f b/physics/sfc_drv.f
index 513aae26e..0c7a11320 100644
--- a/physics/sfc_drv.f
+++ b/physics/sfc_drv.f
@@ -590,6 +590,13 @@ subroutine lsm_noah_run                                            &
 
 !  perturb vegetation fraction that goes into sflx, use the same
 !  perturbation strategy as for albedo (percentile matching)
+!! Following Gehne et al. (2018) \cite gehne_et_al_2018, a perturbation of vegetation
+!! fraction is added to account for the uncertainty. A percentile matching technique
+!! is applied to guarantee the perturbed vegetation fraction is bounded between 0 and
+!! 1. The standard deviation of the perturbations is 0.25 for vegetation fraction of
+!! 0.5 and the perturbations go to zero as vegetation fraction  approaches its upper 
+!! or lower bound.
+
         vegfp  = vegfpert(i)                    ! sfc-perts, mgehne
         ! sfc perts, mgehne
         if (pertvegf(1)>0.0) then
diff --git a/physics/sflx.f b/physics/sflx.f
index d9ae482ca..19caa0fca 100644
--- a/physics/sflx.f
+++ b/physics/sflx.f
@@ -426,6 +426,15 @@ subroutine gfssflx                                                & !  ---  inpu
 !            z0, czil, xlai, csoil )                                       !
 
 !  --- ...  bexp sfc-perts, mgehne
+!! Following Gehne et al. (2018) \cite gehne_et_al_2018, a perturbation of LAI
+!! "leaf area index" (xlaip) and a perturbation of the empirical exponent parameter
+!! b in the soil hydraulic conductivity calculation (bexpp) are added to account for
+!! the uncertainties of LAI and b associated with different vegetation types and soil 
+!! types using a linear scaling. The spatial pattern of xlaip is drawn from a normal 
+!! distribution with a standard deviation of 0.25 while makes the LAI between 0 and 8.
+!! The spatial pattern of bexpp is drawn from a normal distribution with a standard 
+!! deviation of 0.4, and is bounded between -1 and 1.
+
       if( bexpp < 0.) then
          bexp = bexp * max(1.+bexpp, 0.)
       endif