From 528af347b9846b2dae36c65543ba68f8a5d7b61f Mon Sep 17 00:00:00 2001
From: Matthew Hoffman <mhoffman@lanl.gov>
Date: Thu, 7 May 2026 13:38:31 -0600
Subject: [PATCH] Add option for crevasse water depth to be proportional to
 melt rate

This commit adds a new possible value for
config_crevasse_water_depth_source that allows the crevasse water depth
to be directly proportional to the instantaneous local SMB melt rate.
This is meant to be used as a very crude parameterization that provides
water to crevasses when and where melting occurs, without any
consideration of crevasse water mass balance.  It could be used for
something like monthly mean SMB to provide water to crevasses in the
melt season and not otherwise.
---
 components/mpas-albany-landice/src/Registry.xml            | 4 ++--
 .../mpas-albany-landice/src/mode_forward/mpas_li_calving.F | 7 +++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/components/mpas-albany-landice/src/Registry.xml b/components/mpas-albany-landice/src/Registry.xml
index a6bf14cc9664..6791531aa156 100644
--- a/components/mpas-albany-landice/src/Registry.xml
+++ b/components/mpas-albany-landice/src/Registry.xml
@@ -301,14 +301,14 @@
 		/>
                 <nml_option name="config_crevasse_water_depth_source" type="character" default_value="scalar" units="unitless"
                             description="Source of water depth in crevasses for use with crevasse-depth calving law."
-                            possible_values="'data' (read from input file), 'scalar' (specified by config_crevasse_water_depth), or 'scaled_smb' (a specific fraction of negative SMB)"
+                            possible_values="'data' (read from input file), 'scalar' (specified by config_crevasse_water_depth), 'scaled_smb_cumulative' (accmulates a specific fraction of negative SMB until SMB is no longer negative, at which point it resets), or 'scaled_smb_instantaneous' (proportional to instantaneous negative SMB)."
                 />
                 <nml_option name="config_crevasse_water_depth" type="real" default_value="0.0" units="m"
                             description="Water depth in crevasses for Nick et al. (2010) crevasse depth calving law."
                             possible_values="any non-negative real value"
                 />
                 <nml_option name="config_smb_fraction_to_water_depth" type="real" default_value="1.0" units="unitless"
-                            description="Fraction of surface mass balance to convert to retain as water depth in crevasses for Nick et al. (2010) crevasse depth calving law."
+                        description="Fraction of surface mass balance to convert to retain as water depth in crevasses for Nick et al. (2010) crevasse depth calving law.  When 'config_crevasse_water_depth_source'='scaled_smb_cumulative', this is a scaling of the melt volume on each time step.  When 'config_crevasse_water_depth_source' = 'scaled_smb_instantaneous', this is a direct proportionality between the negative SMB and crevasse water depth.  For example, a value of 4.7472e4 would convert a melt rate of 0.001053 kg/m2/s (10 cm/day, a representative Greenland ablation zone melt rate) to a 50 m crevasse water depth (a representative crevasse depth).  This option is meant to be used for situations like monthly mean melt rates."
                             possible_values="any non-negative real value"
                 />
                 <nml_option name="config_ismip6_retreat_k" type="real" default_value="-170.0" units="m (m^3 s^-1)^-0.4 deg. C^-1"
diff --git a/components/mpas-albany-landice/src/mode_forward/mpas_li_calving.F b/components/mpas-albany-landice/src/mode_forward/mpas_li_calving.F
index 6f4ef09fe1d9..451c4715f62e 100644
--- a/components/mpas-albany-landice/src/mode_forward/mpas_li_calving.F
+++ b/components/mpas-albany-landice/src/mode_forward/mpas_li_calving.F
@@ -4074,7 +4074,7 @@ subroutine crevasse_depth_calving(domain, err)
          crevasseWaterDepth(:) = config_crevasse_water_depth
       elseif (trim(config_crevasse_water_depth_source) == "data") then
          ! Do nothing. This was already retrieved above.
-      elseif (trim(config_crevasse_water_depth_source) == "scaled_smb") then
+      elseif (trim(config_crevasse_water_depth_source) == "scaled_smb_cumulative") then
          where (sfcMassBalApplied < 0.0_RKIND)
              crevasseWaterDepth = crevasseWaterDepth + &
                  (-1.0_RKIND * config_smb_fraction_to_water_depth * &
@@ -4082,8 +4082,11 @@ subroutine crevasse_depth_calving(domain, err)
          elsewhere
              crevasseWaterDepth = 0.0_RKIND
          endwhere
+      elseif (trim(config_crevasse_water_depth_source) == "scaled_smb_instantaneous") then
+         crevasseWaterDepth = config_smb_fraction_to_water_depth * max(0.0_RKIND, -1.0_RKIND * sfcMassBalApplied)
       else
-         call mpas_log_write("config_crevasse_water_depth_source must be set to 'scalar', 'data', or 'scaled_smb'.", MPAS_LOG_ERR)
+         call mpas_log_write("config_crevasse_water_depth_source must be set to 'scalar', 'data', 'scaled_smb_cumulative', " // &
+                             "or 'scaled_smb_instantaneous'.", MPAS_LOG_ERR)
          err = 1
          return
       endif