Kludge to ignore diagnostic stomatal conductance from mosses.

Author: samsrabin

biogeochem/EDPatchDynamicsMod.F90

@@ -3191,7 +3191,28 @@ subroutine fuse_2_patches(csite, dp, rp)
     rp%frac_burnt           = (dp%frac_burnt*dp%area + rp%frac_burnt*rp%area) * inv_sum_area
     rp%btran_ft(:)          = (dp%btran_ft(:)*dp%area + rp%btran_ft(:)*rp%area) * inv_sum_area
     rp%zstar                = (dp%zstar*dp%area + rp%zstar*rp%area) * inv_sum_area
-    rp%c_stomata            = (dp%c_stomata*dp%area + rp%c_stomata*rp%area) * inv_sum_area
+    if (dp%IsAllMoss() .or. rp%IsAllMoss()) then
+       ! We set c_stomata to the unset real value in FatesPlantRespPhotosynthDrive() because mosses
+       ! are expected to have zero resistance. If exactly one fusing patch is all moss, take
+       ! c_stomata from that. This is not accurate, but it's only a diagnostic and for
+       ! one timestep at most (until the next call of FatesPlantRespPhotosynthDrive).
+       ! TODO:
+       !    * If keeping fates_unset_r8 kludge in FatesPlantRespPhotosynthDrive(), code up a way
+       !      to quickly recalculate c_stomata without having to call FatesPlantRespPhotosynthDrive()
+       !      again.
+       !    * Otherwise, c_stomata should always have meaningful values, so remove this special
+       !      handling and just calculate the new value as the area-weighted mean of the donor and
+       !      recipient patches.
+       if (.not. dp%IsAllMoss()) then
+          rp%c_stomata      = dp%c_stomata
+       else if (.not. rp%IsAllMoss()) then
+          rp%c_stomata      = rp%c_stomata
+       else
+          rp%c_stomata      = fates_unset_r8
+       end if
+    else
+       rp%c_stomata         = (dp%c_stomata*dp%area + rp%c_stomata*rp%area) * inv_sum_area
+    end if
     rp%c_lblayer            = (dp%c_lblayer*dp%area + rp%c_lblayer*rp%area) * inv_sum_area
 
     ! Radiation

biogeochem/FatesPatchMod.F90

@@ -241,6 +241,7 @@ module FatesPatchMod
       procedure :: FreeMemory
       procedure :: Dump
       procedure :: CheckVars
+      procedure :: IsAllMoss
 
   end type fates_patch_type
 
@@ -1286,6 +1287,33 @@ subroutine CheckVars(this, var_aliases, return_code)
 
     end subroutine CheckVars
 
+    !===========================================================================
+
+    function IsAllMoss(this)
+      !
+      ! DESCRIPTION:
+      !  Checks whether all cohorts on patch are moss
+
+      ! ARGUMENTS:
+      class(fates_patch_type), intent(inout) :: this
+
+      ! LOCALS:
+      type(fates_cohort_type), pointer :: currentCohort ! cohort object
+
+      ! RESULT:
+      logical :: IsAllMoss
+
+      IsAllMoss = .true.
+      currentCohort => this%tallest
+       do while(associated(currentCohort) .and. IsAllMoss)
+         if (prt_params%moss(currentCohort%pft) == ifalse) then
+           IsAllMoss = .false.
+         end if
+         currentCohort => currentCohort%shorter
+       end do
+
+    end function IsAllMoss
+
     !===========================================================================  
 
 end module FatesPatchMod

biogeophys/FatesPlantRespPhotosynthMod.F90

@@ -1137,7 +1137,9 @@ subroutine FatesPlantRespPhotosynthDrive (nsites, sites,bc_in,bc_out,dtime)
                         ! the inverse of mean leaf conductance
                         r_sb_leaves  = 1.0_r8/g_sb_leaves
 
-                        if (r_sb_leaves<bc_in(s)%rb_pa(ifp)) then
+                        ! Mosses have 0 stomatal resistance, so we actually do expect it to be less
+                        ! than boundary layer resistance
+                        if (r_sb_leaves<bc_in(s)%rb_pa(ifp) .and. .not. currentPatch%IsAllMoss()) then
                            write(fates_log(),*) 'Combined canopy resistance was somehow smaller than'
                            write(fates_log(),*) 'its boundary layer resistance component'
                            write(fates_log(),*) 'r_sb_leaves [s/m]: ',r_sb_leaves
@@ -1165,7 +1167,16 @@ subroutine FatesPlantRespPhotosynthDrive (nsites, sites,bc_in,bc_out,dtime)
                      ! is what is used in the field usually, so we track that form
                      ! vmol_cf :  s m**2/umol -> s/m (ideal gas conversion) [umol/m3]
 
-                     currentPatch%c_stomata  = vmol_cf / r_stomata
+                     if (currentPatch%IsAllMoss()) then
+                        ! Mosses have 0 stomatal resistance, so 1/r_stomata would be infinite
+                        ! and cause floating-point errors.
+                        ! TODO: Is there a better way to handle this? Conductance has units
+                        ! mol (H2O?) m-2 s-1, so can we just do the stoichiometry to get this based 
+                        ! on GPP and respiration?
+                        currentPatch%c_stomata = fates_unset_r8
+                     else
+                        currentPatch%c_stomata  = vmol_cf / r_stomata
+                     end if
 
                   else !if_any_lai