diff --git a/AGCM.rc.tmpl b/AGCM.rc.tmpl
index a5c985d2..3a285b00 100644
--- a/AGCM.rc.tmpl
+++ b/AGCM.rc.tmpl
@@ -535,7 +535,8 @@ RECORD_REF_TIME: >>>REFTIME<<< >>>FCSTIME<<<
 
 # Choice for Land Surface Model
 #      1 : Catchment
-#      2 : CatchmentCNCLM40
+#      2 : Catchment-CN4.0 (CNCLM40)
+#      4 : Catchment-CN5.1 (CNCLM51)
 # ------------------------------------------------------------
 LSM_CHOICE: @LSM_CHOICE
 
@@ -558,7 +559,7 @@ LSM_CHOICE: @LSM_CHOICE
 # -------   not from this file.                            -------
 # Atmosphere-Land CO2 coupling
 # ----------------------------
-# USE_CNNEE: 0 #  options : 0 (default); 1 (Chem uses NNEE from CatchmentCN, NOTE you must add USE_CNNEE: 1 to CO2_GridComp.rc and AMIP/CO2_GridComp.rc,
+# USE_CNNEE: 0 #  options : 0 (default); 1 (Chem uses NEE from CatchmentCN, NOTE you must add USE_CNNEE: 1 to CO2_GridComp.rc and AMIP/CO2_GridComp.rc,
 #                           in GOCART/ESMF/GOCART_GridComp/CO2_GridComp/ before you build the model.)
 #
 # ----------------------------------------------------------------
@@ -610,6 +611,10 @@ MAPL_ENABLE_BOOTSTRAP: @BOOT
 @MODELATMCATCHCNCLM40_INTERNAL_CHECKPOINT_FILE:  catchcn_internal_checkpoint
 @MODELATMCATCHCNCLM40_INTERNAL_CHECKPOINT_TYPE:  @CHECKPOINT_TYPE
 
+@MODELATMCATCHCNCLM51_INTERNAL_RESTART_FILE:     catchcn_internal_rst
+@MODELATMCATCHCNCLM51_INTERNAL_CHECKPOINT_FILE:  catchcn_internal_checkpoint
+@MODELATMCATCHCNCLM51_INTERNAL_CHECKPOINT_TYPE:  @CHECKPOINT_TYPE
+
 @MODELATMMOIST_INTERNAL_RESTART_FILE:            moist_internal_rst
 @MODELATMMOIST_INTERNAL_CHECKPOINT_FILE:         moist_internal_checkpoint
 @MODELATMMOIST_INTERNAL_CHECKPOINT_TYPE:         @CHECKPOINT_TYPE
diff --git a/HISTORY.AGCM.rc.tmpl b/HISTORY.AGCM.rc.tmpl
index 7eb012c8..4abbd3b9 100644
--- a/HISTORY.AGCM.rc.tmpl
+++ b/HISTORY.AGCM.rc.tmpl
@@ -282,6 +282,8 @@ PC@HIST_IMx@HIST_JM-DC.LM: @AGCM_LM
 @HIST_CATCHCN               'CNNPP'          , 'SURFACE'     ,
 @HIST_CATCHCN               'CNGPP'          , 'SURFACE'     ,
 @HIST_CATCHCN               'CNSR'           , 'SURFACE'     ,
+@HIST_CATCHCN               'CNAR'           , 'SURFACE'     ,
+@HIST_CATCHCN               'CNHR'           , 'SURFACE'     ,
 @HIST_CATCHCN               'CNNEE'          , 'SURFACE'     ,
 @HIST_CATCHCN               'CNXSMR'         , 'SURFACE'     ,
 @HIST_CATCHCN               'CNADD'          , 'SURFACE'     ,
diff --git a/gcm_run.j b/gcm_run.j
index 4e7aeb62..50859d25 100755
--- a/gcm_run.j
+++ b/gcm_run.j
@@ -334,7 +334,7 @@ chmod +x linkbcs
 
 @GCMRUN_CATCHCNset LSM_CHOICE = `grep LSM_CHOICE:  AGCM.rc | cut -d':' -f2`
 @GCMRUN_CATCHCNif ($LSM_CHOICE == 2) then
-@GCMRUN_CATCHCN  grep -v "'CNFROOTC'" HISTORY.rc > Hist_tmp.rc && mv Hist_tmp.rc HISTORY.rc
+@GCMRUN_CATCHCN  grep -v "'CNFROOTC'" HISTORY.rc | grep -v "'CNAR'" | grep -v "'CNHR'" > Hist_tmp.rc && mv Hist_tmp.rc HISTORY.rc
 @GCMRUN_CATCHCNendif
 #######################################################################
 #                  Setup executable
diff --git a/gcm_setup b/gcm_setup
index 573ab63f..98b68d06 100755
--- a/gcm_setup
+++ b/gcm_setup
@@ -1434,14 +1434,14 @@ LSM_BCS:
 # things out with something. So we use the default Land settings.
 
 if ($DATA_ATMOS == TRUE) then
-  set LSM_BCS = "NL3"
-  set LSM_CHOICE  = 1
-  set LSM_BCS      = "NL3"
-  set LSM_PARMS    = ""
-  set EMIP_BCS_IN  = "NL3"
-  set EMIP_OLDLAND = "#DELETE"
-  set EMIP_NEWLAND = ""
-  set EMIP_MERRA2  = "MERRA2_NewLand"
+  set LSM_BCS        = "NL3"
+  set LSM_CHOICE     = 1
+  set LSM_BCS        = "NL3"
+  set LSM_PARMS      = ""
+  set EMIP_BCS_IN    = "NL3"
+  set EMIP_OLDLAND   = "#DELETE"
+  set EMIP_NEWLAND   = ""
+  set EMIP_MERRA2    = "MERRA2_NewLand"
   set HIST_CATCHCN   = "#DELETE"
   set GCMRUN_CATCHCN = "#DELETE"
 else
@@ -1479,12 +1479,12 @@ endif
 # Enter Catch-Carbon
 # ----------------------
 LSM_CHOICE:
-echo "Enter the choice of ${C1} Land Surface Model${CN} using: ${C2}1${CN} (Default: Catchment) or ${C2}2${CN} (CatchmentCN-CLM4.0 (CN_CLM40))"
+echo "Enter the choice of ${C1} land surface model${CN} using: ${C2}1${CN} (Default: Catchment), ${C2}2${CN} (Catchment-CN4.0), or ${C2}4${CN} (Catchment-CN5.1)"
 set   LSM_CHOICE = $<
 if( .$LSM_CHOICE == . ) set LSM_CHOICE  = 1
-if(  $LSM_CHOICE != 1 & $LSM_CHOICE != 2 ) then
+if(  $LSM_CHOICE != 1 & $LSM_CHOICE != 2 & $LSM_CHOICE != 4 ) then
     echo
-    echo "${C1} Catchment Model${CN} must be set equal to ${C2}1${CN} or ${C2}2${CN}!"
+    echo "${C1} Land surface model${CN} must be set equal to ${C2}1${CN}, ${C2}2${CN}, or ${C2}4${CN}!"
     goto LSM_CHOICE
 else
     echo
@@ -1492,7 +1492,7 @@ endif
 if( $LSM_CHOICE == 1 ) then
     set HIST_CATCHCN   = "#DELETE"
     set GCMRUN_CATCHCN = "#DELETE"
-else if( $LSM_CHOICE == 2 ) then
+else if( $LSM_CHOICE == 2 || $LSM_CHOICE == 4 ) then
     set HIST_CATCHCN   = ""
     set GCMRUN_CATCHCN = ""
 endif
@@ -2739,9 +2739,13 @@ endif
 /bin/mv $EXPDIR/RC/GEOS_SurfaceGridComp.rc $EXPDIR/RC/GEOS_SurfaceGridComp.tmp
 cat $EXPDIR/RC/GEOS_SurfaceGridComp.tmp | sed -e 's?# GEOSagcm=>?            ?g' > $EXPDIR/RC/GEOS_SurfaceGridComp.rc
 
-if( $LSM_CHOICE == 2 ) then
+if( $LSM_CHOICE == 2 || $LSM_CHOICE == 4 ) then
     /bin/mv $EXPDIR/RC/GEOS_SurfaceGridComp.rc $EXPDIR/RC/GEOS_SurfaceGridComp.tmp
-    cat $EXPDIR/RC/GEOS_SurfaceGridComp.tmp | sed -e '/^ *LAND_PARAMS:/ s/NRv7.2/CN_CLM40/' > $EXPDIR/RC/GEOS_SurfaceGridComp.rc
+    if(     $LSM_CHOICE == 2 ) then
+	cat $EXPDIR/RC/GEOS_SurfaceGridComp.tmp | sed -e '/^ *LAND_PARAMS:/ s/NRv7.2/CN_CLM40/' > $EXPDIR/RC/GEOS_SurfaceGridComp.rc
+    elseif( $LSM_CHOICE == 4 ) then
+	cat $EXPDIR/RC/GEOS_SurfaceGridComp.tmp | sed -e '/^ *LAND_PARAMS:/ s/NRv7.2/CN_CLM51/' > $EXPDIR/RC/GEOS_SurfaceGridComp.rc
+    endif
 endif
 
 if( $LSM_BCS == "ICA" ) then
diff --git a/linkbcs.tmpl b/linkbcs.tmpl
index 7610c99d..78b988e5 100644
--- a/linkbcs.tmpl
+++ b/linkbcs.tmpl
@@ -58,6 +58,7 @@ setenv BCRSLV    @ATMOStag_@OCEANtag
 
 @GCMRUN_CATCHCNif ( -f $BCSDIR/$BCRSLV/lnfm_clim_@AGCM_IMx@AGCM_JM.data  ) /bin/ln -sf $BCSDIR/$BCRSLV/lnfm_clim_@AGCM_IMx@AGCM_JM.data lnfm.data
 @GCMRUN_CATCHCN/bin/ln -s $BCSDIR/land/shared/CO2_MonthlyMean_DiurnalCycle.nc4
+@GCMRUN_CATCHCN/bin/ln -s $BCSDIR/land/shared/ctsm51_params.c210923_forCNCLM.nc
 
 
 set MERRA2OX_SPECIES = "#"