From 892b4f66a1ece8e76ab996646fe8511eeb354fbc Mon Sep 17 00:00:00 2001
From: mvdebolskiy <nomatdebol@gmail.com>
Date: Thu, 12 Mar 2026 12:02:53 -0600
Subject: [PATCH 1/2] make irrigate false a default for fates, restrict
 irrigate to be true with fates

---
 bld/CLMBuildNamelist.pm                       | 5 ++++-
 bld/namelist_files/namelist_defaults_ctsm.xml | 9 +++++----
 src/main/clm_driver.F90                       | 5 +++++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/bld/CLMBuildNamelist.pm b/bld/CLMBuildNamelist.pm
index d433ba8698..885e074c14 100755
--- a/bld/CLMBuildNamelist.pm
+++ b/bld/CLMBuildNamelist.pm
@@ -2084,13 +2084,16 @@ sub setup_logic_irrigate {
   my ($opts, $nl_flags, $definition, $defaults, $nl) = @_;
 
   add_default($opts,  $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, 'irrigate',
-                'use_crop'=>$nl_flags->{'use_crop'}, 'use_cndv'=>$nl_flags->{'use_cndv'},
+                'use_crop'=>$nl_flags->{'use_crop'}, 'use_cndv'=>$nl_flags->{'use_cndv'}, 'use_fates'=>$nl_flags->{'use_fates'},
                 'sim_year'=>$nl_flags->{'sim_year'}, 'sim_year_range'=>$nl_flags->{'sim_year_range'}, );
   if ( &value_is_true($nl->get_value('irrigate') ) ) {
      $nl_flags->{'irrigate'} = ".true.";
      if ( $nl_flags->{'sim_year'} eq "PtVg" ) {
         $log->fatal_error("irrigate=TRUE does NOT make sense with the Potential Vegetation dataset, leave irrigate=FALSE");
      }
+     if (&value_is_true($nl_flags->{'use_fates'})) {
+        $log->fatal_error("irrigate=TRUE is NOT possible with use_fates=TRUE, leave irrigate=FALSE");
+     }
   } else {
      $nl_flags->{'irrigate'} = ".false.";
   }
diff --git a/bld/namelist_files/namelist_defaults_ctsm.xml b/bld/namelist_files/namelist_defaults_ctsm.xml
index 25d4b53fac..26d392c0e6 100644
--- a/bld/namelist_files/namelist_defaults_ctsm.xml
+++ b/bld/namelist_files/namelist_defaults_ctsm.xml
@@ -200,10 +200,11 @@ attributes from the config_cache.xml file (with keys converted to upper-case).
 <stream_model_year_align_atm_c13  sim_year_range="1850-2000" >1700</stream_model_year_align_atm_c13>
 
 <!-- Irrigation default (Note, the use-cases also set this) -->
-<irrigate                                                             >.false.</irrigate>
-<irrigate               use_cndv=".false."  sim_year_range="1850-2100">.true.</irrigate>
-<irrigate phys="clm6_0" use_cndv=".false."  sim_year_range="1850-2000">.true.</irrigate>
-<irrigate phys="clm4_5" use_cndv=".false."  sim_year_range="1850-2100">.false.</irrigate>
+<irrigate                                                                                  >.false.</irrigate>
+<irrigate                                                              use_fates=".true."  >.false.</irrigate>
+<irrigate               use_cndv=".false."  sim_year_range="1850-2100" use_fates=".false." >.true.</irrigate>
+<irrigate phys="clm6_0" use_cndv=".false."  sim_year_range="1850-2000" use_fates=".false." >.true.</irrigate>
+<irrigate phys="clm4_5" use_cndv=".false."  sim_year_range="1850-2100"                     >.false.</irrigate>
 
 <!-- Saturation excess runoff for crops  -->
 <crop_fsat_equals_zero>.false.</crop_fsat_equals_zero>
diff --git a/src/main/clm_driver.F90 b/src/main/clm_driver.F90
index ad97911736..c43ca9a2ee 100644
--- a/src/main/clm_driver.F90
+++ b/src/main/clm_driver.F90
@@ -120,6 +120,7 @@ subroutine clm_drv(doalb, nextsw_cday, declinp1, declin, rstwr, nlend, rdate, ro
     use FATESFireFactoryMod   , only : scalar_lightning
     use FatesInterfaceTypesMod, only : fates_dispersal_cadence_none
     use CIsoAtmTimeseriesMod, only : C14BombSpike, C13TimeSeries
+    use shr_log_mod, only : errMsg => shr_log_errMsg
     !
     ! !ARGUMENTS:
     implicit none
@@ -822,6 +823,10 @@ subroutine clm_drv(doalb, nextsw_cday, declinp1, declin, rstwr, nlend, rdate, ro
 
        if (irrigate) then
 
+          if (use_fates) then
+            call endrun(msg=' ERROR: somehow use_fates and irrigate are both set to TRUE ' // &
+               errMsg(sourcefile, __LINE__))
+          endif
           ! ============================================================================
           ! Determine irrigation needed for future time steps
           ! ============================================================================

From 5213525c5450c6fd82eafa1ceb6ba1931a384aab Mon Sep 17 00:00:00 2001
From: mvdebolskiy <nomatdebol@gmail.com>
Date: Sat, 14 Mar 2026 11:10:00 -0600
Subject: [PATCH 2/2] Make errmsg more useful and shorter

---
 src/main/clm_driver.F90 | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/main/clm_driver.F90 b/src/main/clm_driver.F90
index c43ca9a2ee..04fff94669 100644
--- a/src/main/clm_driver.F90
+++ b/src/main/clm_driver.F90
@@ -824,8 +824,10 @@ subroutine clm_drv(doalb, nextsw_cday, declinp1, declin, rstwr, nlend, rdate, ro
        if (irrigate) then
 
           if (use_fates) then
-            call endrun(msg=' ERROR: somehow use_fates and irrigate are both set to TRUE ' // &
-               errMsg(sourcefile, __LINE__))
+             call endrun(msg=' ERROR: Can not have ' // &
+                             'use_fates = .true. and irrigate = .true. ' // &
+                             'Set one of them to .false. in your user_nl_clm. ' // &
+                             errMsg(sourcefile, __LINE__))
           endif
           ! ============================================================================
           ! Determine irrigation needed for future time steps