DassHydro · inoelloc · Aug 27, 2026 · Jul 30, 2026 · Jul 30, 2026
diff --git a/doc/source/math_num_documentation/forward_structure.rst b/doc/source/math_num_documentation/forward_structure.rst
@@ -35,7 +35,7 @@ Snow operator :math:`\mathcal{M}_{snw}`
     :align: center
     :width: 300
 
-.. dropdown:: zero (Zero Snow)
+.. dropdown:: Zero Snow (zero)
     :animate: fade-in-slide-down
 
     This snow operator simply means that there is no snow operator.
@@ -46,7 +46,7 @@ Snow operator :math:`\mathcal{M}_{snw}`
 
     with :math:`m_{lt}` the melt flux.
 
-.. dropdown:: ssn (Simple Snow)
+.. dropdown:: Simple Snow (ssn)
     :animate: fade-in-slide-down
 
     This snow operator is a simple degree-day snow operator. It can be expressed as follows:
@@ -1736,6 +1736,19 @@ surface discharge can inflow the current cell :math:`x` - each cell has a unique
     :align: center
     :width: 300
 
+.. _math_num_documentation.forward_structure.routing_module.zero:
+
+.. dropdown:: Zero Routing (zero)
+    :animate: fade-in-slide-down
+
+    This routing operator simply means that there is no routing operator.
+
+    .. math::
+
+        Q(x, t) = \alpha(x) q_t(x, t)
+
+    with :math:`\alpha` a conversion factor from :math:`mm.\Delta t^{-1}` to :math:`m^3.s^{-1}` for a single cell.
+
 .. _math_num_documentation.forward_structure.routing_module.lag0:
 
 .. dropdown:: Instantaneous Routing (lag0)

diff --git a/smash/_constant.py b/smash/_constant.py
@@ -17,21 +17,31 @@ def get_structure() -> list[str]:
 
 def get_rr_parameters_from_structure(structure: str) -> list[str]:
     rr_parameters = []
-    [rr_parameters.extend(MODULE_RR_PARAMETERS[module]) for module in structure.split("-")]
+    sm, hm, rm = structure.split("-")
+    rr_parameters.extend(SNOW_MODULE_RR_PARAMETERS[sm])
+    rr_parameters.extend(HYDROLOGICAL_MODULE_RR_PARAMETERS[hm])
+    rr_parameters.extend(ROUTING_MODULE_RR_PARAMETERS[rm])
 
     return rr_parameters
 
 
 def get_rr_states_from_structure(structure: str) -> list[str]:
     rr_states = []
-    [rr_states.extend(MODULE_RR_STATES[module]) for module in structure.split("-")]
+    sm, hm, rm = structure.split("-")
+    rr_states.extend(SNOW_MODULE_RR_STATES[sm])
+    rr_states.extend(HYDROLOGICAL_MODULE_RR_STATES[hm])
+    rr_states.extend(ROUTING_MODULE_RR_STATES[rm])
 
     return rr_states
 
 
 def get_rr_internal_fluxes_from_structure(structure: str) -> list[str]:
     rr_internal_fluxes = []
-    [rr_internal_fluxes.extend(MODULE_RR_INTERNAL_FLUXES[module]) for module in structure.split("-")]
+    sm, hm, rm = structure.split("-")
+    rr_internal_fluxes.extend(SNOW_MODULE_RR_INTERNAL_FLUXES[sm])
+    rr_internal_fluxes.extend(HYDROLOGICAL_MODULE_RR_INTERNAL_FLUXES[hm])
+    rr_internal_fluxes.extend(ROUTING_MODULE_RR_INTERNAL_FLUXES[rm])
+
     return rr_internal_fluxes
 
 
@@ -74,7 +84,7 @@ def get_neurons_from_hydrological_module(hydrological_module: str, hidden_neuron
     "vic3l",
 ]
 
-ROUTING_MODULE = ["lag0", "lr", "kw"]
+ROUTING_MODULE = ["zero", "lag0", "lr", "kw"]
 
 MODULE = SNOW_MODULE + HYDROLOGICAL_MODULE + ROUTING_MODULE
 
@@ -111,14 +121,7 @@ def get_neurons_from_hydrological_module(hydrological_module: str, hidden_neuron
 
 # % Following ROUTING_MODULE order
 ROUTING_MODULE_RR_PARAMETERS = dict(
-    zip(ROUTING_MODULE, [[], ["llr"], ["akw", "bkw"]])  # % lag0  # % lr  # % kw
-)
-
-# % Following MODULE order
-MODULE_RR_PARAMETERS = dict(
-    **SNOW_MODULE_RR_PARAMETERS,
-    **HYDROLOGICAL_MODULE_RR_PARAMETERS,
-    **ROUTING_MODULE_RR_PARAMETERS,
+    zip(ROUTING_MODULE, [[], [], ["llr"], ["akw", "bkw"]])  # % zero, lag0, lr, kw
 )
 
 # % Following SNOW_MODULE order
@@ -151,15 +154,12 @@ def get_neurons_from_hydrological_module(hydrological_module: str, hidden_neuron
 
 # % Following ROUTING_MODULE order
 ROUTING_MODULE_RR_STATES = dict(
-    zip(ROUTING_MODULE, [[], ["hlr"], []])  # % lag0  # % lr  # % kw
+    zip(ROUTING_MODULE, [[], [], ["hlr"], []])  # % zero, lag0, lr, kw
 )
 
-# % Following MODULE order
-MODULE_RR_STATES = dict(**SNOW_MODULE_RR_STATES, **HYDROLOGICAL_MODULE_RR_STATES, **ROUTING_MODULE_RR_STATES)
-
 # % Following ROUTING_MODULE order
 ROUTING_MODULE_NQZ = dict(
-    zip(ROUTING_MODULE, [1, 1, 2])  # % lag0  # % lr  # % kw
+    zip(ROUTING_MODULE, [1, 1, 1, 2])  # % zero, lag0, lr, kw
 )
 
 # % Following SNOW_MODULE order
@@ -197,13 +197,7 @@ def get_neurons_from_hydrological_module(hydrological_module: str, hidden_neuron
 
 # % Following ROUTING_MODULE order
 ROUTING_MODULE_RR_INTERNAL_FLUXES = dict(
-    zip(ROUTING_MODULE, [["qup"], ["qup"], ["qim1j"]])  # % lag0  # % lr  # % kw
-)
-
-MODULE_RR_INTERNAL_FLUXES = dict(
-    **SNOW_MODULE_RR_INTERNAL_FLUXES,
-    **HYDROLOGICAL_MODULE_RR_INTERNAL_FLUXES,
-    **ROUTING_MODULE_RR_INTERNAL_FLUXES,
+    zip(ROUTING_MODULE, [[], ["qup"], ["qup"], ["qim1j"]])  # % zero, lag0, lr, kw
 )
 
 ### STRUCTURE ###

diff --git a/smash/core/model/model.py b/smash/core/model/model.py
@@ -141,6 +141,7 @@ class Model:
         routing_module : `str`, default 'lr'
             Name of routing module. Should be one of:
 
+            - ``'zero'``
             - ``'lag0'``
             - ``'lr'``
             - ``'kw'``

diff --git a/smash/fcore/forward/forward_db.f90 b/smash/fcore/forward/forward_db.f90
@@ -26781,6 +26781,10 @@ SUBROUTINE SIMULATION_CHECKPOINT_D(setup, mesh, input_data, parameters&
       END SELECT
 ! Routing module
       SELECT CASE  (setup%routing_module) 
+      CASE ('zero') 
+! 'zero' module
+        checkpoint_variable_d%ac_qz = checkpoint_variable_d%ac_qtz
+        checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
       CASE ('lag0') 
 ! 'lag0' module
         CALL LAG0_TIME_STEP_D(setup, mesh, options, returns, t, &
@@ -27748,6 +27752,10 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
       END SELECT
 ! Routing module
       SELECT CASE  (setup%routing_module) 
+      CASE ('zero') 
+! 'zero' module
+        checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
+        CALL PUSHCONTROL3B(1)
       CASE ('lag0') 
 ! 'lag0' module
         CALL PUSHREAL4ARRAY(checkpoint_variable%ac_qz, SIZE(&
@@ -27756,7 +27764,7 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
         CALL LAG0_TIME_STEP(setup, mesh, options, returns, t, &
 &                     checkpoint_variable%ac_qtz, checkpoint_variable%&
 &                     ac_qz)
-        CALL PUSHCONTROL2B(1)
+        CALL PUSHCONTROL3B(2)
       CASE ('lr') 
 ! 'lr' module
 ! % To avoid potential aliasing tapenade warning (DF02)
@@ -27773,7 +27781,7 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
 &                   ac_rr_parameters(:, rr_parameters_inc+1), h1, &
 &                   checkpoint_variable%ac_qz)
         checkpoint_variable%ac_rr_states(:, rr_states_inc+1) = h1
-        CALL PUSHCONTROL2B(2)
+        CALL PUSHCONTROL3B(3)
       CASE ('kw') 
 ! 'kw' module
 ! % akw
@@ -27786,29 +27794,33 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
 &                   ac_rr_parameters(:, rr_parameters_inc+1), &
 &                   checkpoint_variable%ac_rr_parameters(:, &
 &                   rr_parameters_inc+2), checkpoint_variable%ac_qz)
-        CALL PUSHCONTROL2B(3)
+        CALL PUSHCONTROL3B(4)
       CASE DEFAULT
-        CALL PUSHCONTROL2B(0)
+        CALL PUSHCONTROL3B(0)
       END SELECT
       CALL STORE_TIME_STEP(setup, mesh, output, returns, &
 &                    checkpoint_variable, t)
     END DO
     DO t=end_time_step,start_time_step,-1
       CALL STORE_TIME_STEP_B(setup, mesh, output, output_b, returns, &
 &                      checkpoint_variable, checkpoint_variable_b, t)
-      CALL POPCONTROL2B(branch)
+      CALL POPCONTROL3B(branch)
       IF (branch .LT. 2) THEN
         IF (branch .NE. 0) THEN
-          CALL POPREAL4ARRAY(checkpoint_variable%ac_qz, SIZE(&
-&                      checkpoint_variable%ac_qz, 1)*SIZE(&
-&                      checkpoint_variable%ac_qz, 2))
-          CALL LAG0_TIME_STEP_B(setup, mesh, options, returns, t, &
-&                         checkpoint_variable%ac_qtz, &
-&                         checkpoint_variable_b%ac_qtz, &
-&                         checkpoint_variable%ac_qz, &
-&                         checkpoint_variable_b%ac_qz)
+          checkpoint_variable_b%ac_qtz = checkpoint_variable_b%ac_qtz + &
+&           checkpoint_variable_b%ac_qz
+          checkpoint_variable_b%ac_qz = 0.0_4
         END IF
       ELSE IF (branch .EQ. 2) THEN
+        CALL POPREAL4ARRAY(checkpoint_variable%ac_qz, SIZE(&
+&                    checkpoint_variable%ac_qz, 1)*SIZE(&
+&                    checkpoint_variable%ac_qz, 2))
+        CALL LAG0_TIME_STEP_B(setup, mesh, options, returns, t, &
+&                       checkpoint_variable%ac_qtz, &
+&                       checkpoint_variable_b%ac_qtz, &
+&                       checkpoint_variable%ac_qz, checkpoint_variable_b&
+&                       %ac_qz)
+      ELSE IF (branch .EQ. 3) THEN
         h1_b = 0.0_4
         h1_b = checkpoint_variable_b%ac_rr_states(:, rr_states_inc+1)
         CALL POPREAL4ARRAY(h1, mesh%nac)
@@ -29720,6 +29732,9 @@ SUBROUTINE SIMULATION_CHECKPOINT(setup, mesh, input_data, parameters, &
       END SELECT
 ! Routing module
       SELECT CASE  (setup%routing_module) 
+      CASE ('zero') 
+! 'zero' module
+        checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
       CASE ('lag0') 
 ! 'lag0' module
         CALL LAG0_TIME_STEP(setup, mesh, options, returns, t, &

diff --git a/smash/fcore/forward/forward_openmp_db.f90 b/smash/fcore/forward/forward_openmp_db.f90
@@ -28030,6 +28030,10 @@ SUBROUTINE SIMULATION_CHECKPOINT_D(setup, mesh, input_data, parameters&
       END SELECT
 ! Routing module
       SELECT CASE  (setup%routing_module) 
+      CASE ('zero') 
+! 'zero' module
+        checkpoint_variable_d%ac_qz = checkpoint_variable_d%ac_qtz
+        checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
       CASE ('lag0') 
 ! 'lag0' module
         CALL LAG0_TIME_STEP_D(setup, mesh, options, returns, t, &
@@ -28997,6 +29001,10 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
       END SELECT
 ! Routing module
       SELECT CASE  (setup%routing_module) 
+      CASE ('zero') 
+! 'zero' module
+        checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
+        CALL PUSHCONTROL3B(1)
       CASE ('lag0') 
 ! 'lag0' module
         CALL PUSHREAL4ARRAY(checkpoint_variable%ac_qz, SIZE(&
@@ -29005,7 +29013,7 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
         CALL LAG0_TIME_STEP(setup, mesh, options, returns, t, &
 &                     checkpoint_variable%ac_qtz, checkpoint_variable%&
 &                     ac_qz)
-        CALL PUSHCONTROL2B(1)
+        CALL PUSHCONTROL3B(2)
       CASE ('lr') 
 ! 'lr' module
 ! % To avoid potential aliasing tapenade warning (DF02)
@@ -29022,7 +29030,7 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
 &                   ac_rr_parameters(:, rr_parameters_inc+1), h1, &
 &                   checkpoint_variable%ac_qz)
         checkpoint_variable%ac_rr_states(:, rr_states_inc+1) = h1
-        CALL PUSHCONTROL2B(2)
+        CALL PUSHCONTROL3B(3)
       CASE ('kw') 
 ! 'kw' module
 ! % akw
@@ -29035,29 +29043,33 @@ SUBROUTINE SIMULATION_CHECKPOINT_B(setup, mesh, input_data, parameters&
 &                   ac_rr_parameters(:, rr_parameters_inc+1), &
 &                   checkpoint_variable%ac_rr_parameters(:, &
 &                   rr_parameters_inc+2), checkpoint_variable%ac_qz)
-        CALL PUSHCONTROL2B(3)
+        CALL PUSHCONTROL3B(4)
       CASE DEFAULT
-        CALL PUSHCONTROL2B(0)
+        CALL PUSHCONTROL3B(0)
       END SELECT
       CALL STORE_TIME_STEP(setup, mesh, output, returns, &
 &                    checkpoint_variable, t)
     END DO
     DO t=end_time_step,start_time_step,-1
       CALL STORE_TIME_STEP_B(setup, mesh, output, output_b, returns, &
 &                      checkpoint_variable, checkpoint_variable_b, t)
-      CALL POPCONTROL2B(branch)
+      CALL POPCONTROL3B(branch)
       IF (branch .LT. 2) THEN
         IF (branch .NE. 0) THEN
-          CALL POPREAL4ARRAY(checkpoint_variable%ac_qz, SIZE(&
-&                      checkpoint_variable%ac_qz, 1)*SIZE(&
-&                      checkpoint_variable%ac_qz, 2))
-          CALL LAG0_TIME_STEP_B(setup, mesh, options, returns, t, &
-&                         checkpoint_variable%ac_qtz, &
-&                         checkpoint_variable_b%ac_qtz, &
-&                         checkpoint_variable%ac_qz, &
-&                         checkpoint_variable_b%ac_qz)
+          checkpoint_variable_b%ac_qtz = checkpoint_variable_b%ac_qtz + &
+&           checkpoint_variable_b%ac_qz
+          checkpoint_variable_b%ac_qz = 0.0_4
         END IF
       ELSE IF (branch .EQ. 2) THEN
+        CALL POPREAL4ARRAY(checkpoint_variable%ac_qz, SIZE(&
+&                    checkpoint_variable%ac_qz, 1)*SIZE(&
+&                    checkpoint_variable%ac_qz, 2))
+        CALL LAG0_TIME_STEP_B(setup, mesh, options, returns, t, &
+&                       checkpoint_variable%ac_qtz, &
+&                       checkpoint_variable_b%ac_qtz, &
+&                       checkpoint_variable%ac_qz, checkpoint_variable_b&
+&                       %ac_qz)
+      ELSE IF (branch .EQ. 3) THEN
         h1_b = 0.0_4
         h1_b = checkpoint_variable_b%ac_rr_states(:, rr_states_inc+1)
         CALL POPREAL4ARRAY(h1, mesh%nac)
@@ -30969,6 +30981,9 @@ SUBROUTINE SIMULATION_CHECKPOINT(setup, mesh, input_data, parameters, &
       END SELECT
 ! Routing module
       SELECT CASE  (setup%routing_module) 
+      CASE ('zero') 
+! 'zero' module
+        checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
       CASE ('lag0') 
 ! 'lag0' module
         CALL LAG0_TIME_STEP(setup, mesh, options, returns, t, &

diff --git a/smash/fcore/forward/md_simulation.f90 b/smash/fcore/forward/md_simulation.f90
@@ -856,6 +856,11 @@ subroutine simulation_checkpoint(setup, mesh, input_data, parameters, output, op
             ! Routing module
             select case (setup%routing_module)
 
+                ! 'zero' module
+            case ("zero")
+
+                checkpoint_variable%ac_qz = checkpoint_variable%ac_qtz
+
                 ! 'lag0' module
             case ("lag0")
 

diff --git a/smash/tests/baseline.hdf5 b/smash/tests/baseline.hdf5