diff --git a/bld/build-namelist b/bld/build-namelist
index 6ce53e55b3..50dc73eb09 100755
--- a/bld/build-namelist
+++ b/bld/build-namelist
@@ -2962,9 +2962,17 @@ if ($maxzen>0.0) {
 # upper boundary specifier
 my $ubc_ver;
 if (($chem =~ /waccm_ma/ or $chem =~ /waccm_tsmlt/ or $chem =~ /waccm_t4ma/) and !$waccmx) {
-    $ubc_ver = 'waccmchem';
+    if ($phys =~ /cam7/) {
+	$ubc_ver = 'waccm7chem';
+    } else {
+	$ubc_ver = 'waccmchem';
+    }
 } elsif ($chem =~ /waccm_sc/ or ($model_top eq "ht" and $chem =~ /ghg_mam/)) {
-    $ubc_ver = 'waccmsc';
+    if ($phys =~ /cam7/) {
+	$ubc_ver = 'waccm7sc';
+    } else {
+	$ubc_ver = 'waccmsc';
+    }
 }
 if (defined $ubc_ver) {
     add_default($nl, 'ubc_specifier', 'ver'=>$ubc_ver);
diff --git a/bld/namelist_files/namelist_defaults_cam.xml b/bld/namelist_files/namelist_defaults_cam.xml
index 007e115d8e..2e1b4da8bd 100644
--- a/bld/namelist_files/namelist_defaults_cam.xml
+++ b/bld/namelist_files/namelist_defaults_cam.xml
@@ -2098,6 +2098,13 @@
 <ubc_specifier ver="waccmsc">
   'T->MSIS','Q->2.d-8vmr','CH4->2.d-10vmr'
 </ubc_specifier>
+<!-- WACCM7 -- do not include water vapor for now -->
+<ubc_specifier ver="waccm7chem">
+  'T->MSIS','CH4->2.d-10vmr','F->1.0D-15mmr','HF->1.0D-15mmr','H->MSIS','N->MSIS','O->MSIS','O2->MSIS','H2->TGCM','NO->SNOE'
+</ubc_specifier>
+<ubc_specifier ver="waccm7sc">
+  'T->MSIS','CH4->2.d-10vmr'
+</ubc_specifier>
 
 <!-- Boundary data for Tropopheric Chemistry -->
 <fstrat_file    >atm/cam/chem/trop_mozart/ub/ubvals_b40.20th.track1_1996-2005_c110315.nc</fstrat_file>
diff --git a/bld/namelist_files/use_cases/1850_cam_lt.xml b/bld/namelist_files/use_cases/1850_cam_lt.xml
index 410607c93a..3de46f32f0 100644
--- a/bld/namelist_files/use_cases/1850_cam_lt.xml
+++ b/bld/namelist_files/use_cases/1850_cam_lt.xml
@@ -12,10 +12,12 @@
 <flbc_list>'CO2','CH4','N2O','CFC11','CFC12','CFC11eq'</flbc_list>
 
 <!-- Low top upper boundary conditions -->
+<!-- Remove for now
 <ubc_specifier>'Q:H2O->UBC_FILE'</ubc_specifier>
 <ubc_file_path>atm/cam/chem/ubc/b.e21.BWHIST.f09_g17.CMIP6-historical-WACCM.ensAvg123.cam.h0zm.H2O.1849-2014_c240604.nc</ubc_file_path>
 <ubc_file_input_type>CYCLICAL</ubc_file_input_type>
 <ubc_file_cycle_yr>1850</ubc_file_cycle_yr>
+ -->
 
 <!-- ozone data :  -->
 <prescribed_ozone_datapath>   'atm/cam/ozone_strataero'  </prescribed_ozone_datapath>
diff --git a/bld/namelist_files/use_cases/hist_cam_lt.xml b/bld/namelist_files/use_cases/hist_cam_lt.xml
index 79da9c39c7..f34c10eb3c 100644
--- a/bld/namelist_files/use_cases/hist_cam_lt.xml
+++ b/bld/namelist_files/use_cases/hist_cam_lt.xml
@@ -11,9 +11,11 @@
 <flbc_list>'CO2','CH4','N2O','CFC11','CFC12','CFC11eq'</flbc_list>
 
 <!-- Low top upper boundary conditions -->
+<!-- Remove for now
 <ubc_specifier>'Q:H2O->UBC_FILE'</ubc_specifier>
 <ubc_file_path>atm/cam/chem/ubc/b.e21.BWHIST.f09_g17.CMIP6-historical-WACCM.ensAvg123.cam.h0zm.H2O.1849-2014_c240604.nc</ubc_file_path>
 <ubc_file_input_type>'SERIAL'</ubc_file_input_type>
+ -->
 
 <!-- ozone data -->
 <prescribed_ozone_datapath>   'atm/cam/ozone_strataero'                                                         </prescribed_ozone_datapath>
diff --git a/src/physics/cam7/physpkg.F90 b/src/physics/cam7/physpkg.F90
index 2ef8abdc6a..78d1deba92 100644
--- a/src/physics/cam7/physpkg.F90
+++ b/src/physics/cam7/physpkg.F90
@@ -159,12 +159,14 @@ subroutine phys_register
     use surface_emissions_mod, only: surface_emissions_reg
     use elevated_emissions_mod, only: elevated_emissions_reg
     use ctem_diags_mod, only: ctem_diags_reg
+    use upper_bc,       only: ubc_fixed_conc
 
     !---------------------------Local variables-----------------------------
     !
     integer  :: m        ! loop index
     integer  :: mm       ! constituent index
     integer  :: nmodes
+    logical  :: has_fixed_ubc ! for upper bndy cond
     !-----------------------------------------------------------------------
 
     ! Get physics options
@@ -191,11 +193,12 @@ subroutine phys_register
     ! Register water vapor.
     ! ***** N.B. ***** This must be the first call to cnst_add so that
     !                  water vapor is constituent 1.
+    has_fixed_ubc = ubc_fixed_conc('Q') ! check for fixed concentration upper boundary condition
     if (moist_physics) then
-       call cnst_add('Q', mwh2o, cpwv, 1.E-12_r8, mm, &
+       call cnst_add('Q', mwh2o, cpwv, 1.E-12_r8, mm, fixed_ubc=has_fixed_ubc, &
             longname='Specific humidity', readiv=.true., is_convtran1=.true.)
     else
-       call cnst_add('Q', mwh2o, cpwv, 0.0_r8, mm, &
+       call cnst_add('Q', mwh2o, cpwv, 0.0_r8, mm, fixed_ubc=has_fixed_ubc, &
             longname='Specific humidity', readiv=.false., is_convtran1=.true.)
     end if