Repository: Deltares/Wflow.jl (julia)

Issue:
Remove lower limit of zero for `sbm.runoff`
### Feature type

Changing existing functionality

### Improvement Description

The lower limit of `runoff` of the `SBM` concept is set at zero. This was implemented in the Python version of wflow_sbm, to avoid a very slow kinematic wave solution for surface flow computation (no distinction between a kinematic wave for overland and river flow). When in the Python version of wflow_sbm the kinematic wave for surface flow was split into a river and land component, the lower limit was removed for river runoff, but not for land runoff. It would be good to also remove this lower limit for land runoff, also because it may result in water balance errors.

### Implementation Description

Remove lower limit of zero for `sbm.runoff`.

### Additional Context

_No response_

Pull request:
## Issue addressed
Fixes #372 

## Explanation
See https://github.com/Deltares/Wflow.jl/issues/372.

## Checklist
- [x] Updated tests or added new tests
- [x] Branch is up to date with `master`
- [x] Tests & pre-commit hooks pass
- [x] Updated documentation if needed
- [x] Updated changelog.md if needed

Patch:
diff --git a/docs/src/changelog.md b/docs/src/changelog.md
index bc747bcb6..65f774665 100644
--- a/docs/src/changelog.md
+++ b/docs/src/changelog.md
@@ -24,8 +24,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Close netCDF `NCDataset` with state variables in extended BMI function `save_state`.
 
 ### Changed
-- Stop exposing scalar variables through BMI. The `BMI.get_value_ptr` function was
-  not working correctly for scalar model variables (a `view` was applied). Only a few scalar
+- Stop exposing scalar variables through BMI. The `BMI.get_value_ptr` function was not
+  working correctly for scalar model variables (a `view` was applied). Only a few scalar
   model parameters are defined, and it is not expected that exposing these variables is
   required (e.g. for model coupling) while code changes for these variables (including
   struct fields) are required.
@@ -35,6 +35,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   length `dl` at a ghost node should be set through the model parameter netCDF file
   (`riverlength_bc`), providing this boundary condition through the `[model]` settings in
   the TOML file (`model.riverlength_bc`) has been deprecated.
+- As part of the vertical `SBM` concept: 1) add variable `net_runoff` (land runoff minus
+  actual open water evaporation `ae_openw_l`) and 2) change the definition of variable
+  `runoff` by removing the subtraction of `ae_openw_l` (total land runoff). The variable
+  `net_runoff` is now input to the kinematic wave for overland flow (replaces the original
+  `runoff` variable as input). The lower limit of the original `runoff` variable was set at
+  zero, which may result in water balance errors. This lower limit was implemented in the
+  Python version of wflow\_sbm, to avoid a very slow kinematic wave solution for surface
+  flow computation (no distinction between a kinematic wave for overland and river flow).
+  When in the Python version of wflow\_sbm the kinematic wave for surface flow was split
+  into a river and land component, the lower limit was removed for river runoff
+  (`net_runoff_river`), but not for land runoff.
 
 ### Added
 - Total water storage as an export variable for `SBM` concept. This is the total water stored
diff --git a/docs/src/model_docs/params_vertical.md b/docs/src/model_docs/params_vertical.md
index fde92c15b..214fe3c17 100644
--- a/docs/src/model_docs/params_vertical.md
+++ b/docs/src/model_docs/params_vertical.md
@@ -115,7 +115,8 @@ profile `kv` is used and `z_layered` is required as input.
 | `exfiltustore` | water exfiltrating from unsaturated store because of change in water table | mm Δt``^{-1}`` | - |
 | `excesswatersoil` | excess water for non-compacted fraction | mm Δt``^{-1}`` | - |
 | `excesswaterpath` | excess water for compacted fraction | mm Δt``^{-1}`` | - |
-| `runoff` | total surface runoff from infiltration and saturation excess  | mm Δt``^{-1}`` | - |
+| `runoff` | total surface runoff from infiltration and saturation excess | mm Δt``^{-1}`` | - |
+| `net_runoff` | net surface runoff (`runoff` - `ae_openw_l`) | mm Δt``^{-1}`` | - |
 | `vwc` | volumetric water content per soil layer (including θᵣ and saturated zone)  | - | - |
 | `vwc_perc` | volumetric water content per soil layer (including θᵣ and saturated zone)  | % | - |
 | `rootstore` | root water storage in unsaturated and saturated zone (excluding θᵣ)  | mm| - |
diff --git a/src/flow.jl b/src/flow.jl
index c10087a93..d81873196 100644
--- a/src/flow.jl
+++ b/src/flow.jl
@@ -1644,7 +1644,7 @@ end
 """
     set_land_inwater(model::Model{N,L,V,R,W,T}) where {N,L,V,R,W,T<:SbmGwfModel}
 
-Set `inwater` of the lateral land component for the `SbmGwgModel` type.
+Set `inwater` of the lateral land component for the `SbmGwfModel` type.
 """
 function set_land_inwater(model::Model{N,L,V,R,W,T}) where {N,L,V,R,W,T<:SbmGwfModel}
     @unpack lateral, vertical, network, config = model
@@ -1657,10 +1657,22 @@ function set_land_inwater(model::Model{N,L,V,R,W,T}) where {N,L,V,R,W,T<:SbmGwfM
     end
 
     lateral.land.inwater .=
-        (vertical.runoff .* network.land.xl .* network.land.yl .* 0.001) ./
+        (vertical.net_runoff .* network.land.xl .* network.land.yl .* 0.001) ./
         lateral.land.Δt .+ drainflux
 end
 
+"""
+    set_land_inwater(model::Model{N,L,V,R,W,T}) where {N,L,V,R,W,T<:SbmModel}
+
+Set `inwater` of the lateral land component for the `SbmModel` type.
+"""
+function set_land_inwater(model::Model{N,L,V,R,W,T}) where {N,L,V,R,W,T<:SbmModel}
+    @unpack lateral, vertical, network = model
+    lateral.land.inwater .=
+        (vertical.net_runoff .* network.land.xl .* network.land.yl .* 0.001) ./
+        lateral.land.Δt
+end
+
 """
     set_land_inwater(model)
 
@@ -1794,7 +1806,7 @@ function surface_routing(
     @unpack lateral, vertical, network, clock = model
 
     @. lateral.land.runoff = (
-        (vertical.runoff / 1000.0) * (network.land.xl * network.land.yl) / vertical.Δt +
+        (vertical.net_runoff / 1000.0) * (network.land.xl * network.land.yl) / vertical.Δt +
         ssf_toriver +
         # net_runoff_river
         (
diff --git a/src/sbm.jl b/src/sbm.jl
index ece500ec6..ba508ddb5 100644
--- a/src/sbm.jl
+++ b/src/sbm.jl
@@ -136,8 +136,10 @@
     excesswatersoil::Vector{T}
     # Excess water for compacted fraction [mm Δt⁻¹]
     excesswaterpath::Vector{T}
-    # Total surface runoff from infiltration and saturation excess [mm Δt⁻¹]
+    # Total surface runoff from infiltration and saturation excess (excluding actual open water evaporation) [mm Δt⁻¹]
     runoff::Vector{T}
+    # Net surface runoff (surface runoff - actual open water evaporation) [mm Δt⁻¹]
+    net_runoff::Vector{T}
     # Volumetric water content [-] per soil layer (including θᵣ and saturated zone)
     vwc::Vector{SVector{N,T}} | "-"
     # Volumetric water content [%] per soil layer (including θᵣ and saturated zone)
@@ -632,6 +634,7 @@ function initialize_sbm(nc, config, riverfrac, inds)
         excesswatersoil = fill(mv, n),
         excesswaterpath = fill(mv, n),
         runoff = fill(mv, n),
+        net_runoff = fill(mv, n),
         net_runoff_river = fill(mv, n),
         vwc = svectorscopy(vwc, Val{maxlayers}()),
         vwc_perc = svectorscopy(vwc_perc, Val{maxlayers}()),
@@ -1071,14 +1074,12 @@ function update_after_subsurfaceflow(sbm::SBM, zi, exfiltsatwater)
 
         ustoredepth = sum(@view usld[1:n_usl])
 
-        runoff = max(
+        runoff =
             exfiltustore +
             exfiltsatwater[i] +
             sbm.excesswater[i] +
             sbm.runoff_land[i] +
-            sbm.infiltexcess[i] - sbm.ae_openw_l[i],
-            0.0,
-        )
+            sbm.infiltexcess[i]
 
         # volumetric water content per soil layer and root zone
         vwc = sbm.vwc[i]
@@ -1119,6 +1120,7 @@ function update_after_subsurfaceflow(sbm::SBM, zi, exfiltsatwater)
         sbm.exfiltsatwater[i] = exfiltsatwater[i]
         sbm.exfiltustore[i] = exfiltustore
         sbm.runoff[i] = runoff
+        sbm.net_runoff[i] = runoff - sbm.ae_openw_l[i]
         sbm.vwc[i] = vwc
         sbm.vwc_perc[i] = vwc_perc
         sbm.rootstore[i] = rootstore


Test patch:
diff --git a/server/test/client.jl b/server/test/client.jl
index 5f0f31d2e..45051e81f 100644
--- a/server/test/client.jl
+++ b/server/test/client.jl
@@ -33,8 +33,8 @@ end
 
 @testset "model information functions" begin
     @test request((fn = "get_component_name",)) == Dict("component_name" => "sbm")
-    @test request((fn = "get_input_item_count",)) == Dict("input_item_count" => 192)
-    @test request((fn = "get_output_item_count",)) == Dict("output_item_count" => 192)
+    @test request((fn = "get_input_item_count",)) == Dict("input_item_count" => 193)
+    @test request((fn = "get_output_item_count",)) == Dict("output_item_count" => 193)
     to_check = [
         "vertical.nlayers",
         "vertical.θᵣ",
diff --git a/test/bmi.jl b/test/bmi.jl
index b5e46fb1e..66a97ad46 100644
--- a/test/bmi.jl
+++ b/test/bmi.jl
@@ -20,8 +20,8 @@ tomlpath = joinpath(@__DIR__, "sbm_config.toml")
 
         @testset "model information functions" begin
             @test BMI.get_component_name(model) == "sbm"
-            @test BMI.get_input_item_count(model) == 192
-            @test BMI.get_output_item_count(model) == 192
+            @test BMI.get_input_item_count(model) == 193
+            @test BMI.get_output_item_count(model) == 193
             to_check = [
                 "vertical.nlayers",
                 "vertical.θᵣ",
diff --git a/test/run_sbm.jl b/test/run_sbm.jl
index fed99f23e..148e524b6 100644
--- a/test/run_sbm.jl
+++ b/test/run_sbm.jl
@@ -77,9 +77,12 @@ end
 
     @test sbm.θₛ[50063] ≈ 0.48755401372909546f0
     @test sbm.θᵣ[50063] ≈ 0.15943120419979095f0
-    @test sbm.runoff[50063] == 0.0
-    @test sbm.soilevap[50063] == 0.0
+    @test mean(sbm.runoff) ≈ 0.0416027711985709f0
+    @test mean(sbm.soilevap) ≈ 0.00616346765710303f0
+    @test mean(sbm.actevap) ≈ 0.5393128846181061f0
+    @test mean(sbm.actinfilt) ≈ 1.4860556930083888f0
     @test sbm.snow[5] ≈ 3.592840840467347f0
+    @test mean(sbm.snow) ≈ 0.035197394854698104f0
     @test sbm.total_storage[50063] ≈ 559.70849973344f0
     @test sbm.total_storage[429] ≈ 597.4578475404879f0 # river cell
 end
@@ -91,9 +94,13 @@ model = Wflow.run_timestep(model)
     sbm = model.vertical
     @test sbm.θₛ[50063] ≈ 0.48755401372909546f0
     @test sbm.θᵣ[50063] ≈ 0.15943120419979095f0
-    @test sbm.runoff[50063] == 0.0
-    @test sbm.soilevap[50063] ≈ 0.006358004660566856f0
+    @test mean(sbm.net_runoff) ≈ 0.23657364759232993f0
+    @test mean(sbm.runoff) ≈ 0.2369017651524159f0
+    @test mean(sbm.soilevap) ≈ 0.015275916086112940
+    @test mean(sbm.actevap) ≈ 0.29716147685525746f0
+    @test mean(sbm.actinfilt) ≈ 0.08829600284076534f0
     @test sbm.snow[5] ≈ 3.667748983774868f0
+    @test mean(sbm.snow) ≈ 0.03209680141455693f0
     @test sbm.total_storage[50063] ≈ 559.7935411649405f0
     @test sbm.total_storage[429] ≈ 617.0062092646873f0 # river cell
 end