Remove lower limit of zero for sbm.runoff

docs/src/changelog.md

@@ -35,6 +35,14 @@ 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.
+- Remove lower limit of zero for computation of `runoff` variable of `SBM` vertical concept
+  as it may result in water balance errors. As part of the `runoff` computation, actual open
+  water evaporation `ae_openw_l` is subtracted, which may result in negative `runoff`
+  values. 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, but not for land runoff.
 
 ### Added
 - Total water storage as an export variable for `SBM` concept. This is the total water stored

docs/src/model_docs/params_vertical.md

@@ -115,7 +115,7 @@ 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, saturation excess and actual evaporation (`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| - |

src/sbm.jl

@@ -136,7 +136,7 @@
     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, saturation excess and actual open water evaporation [mm Δt⁻¹]
     runoff::Vector{T}
     # Volumetric water content [-] per soil layer (including θᵣ and saturated zone)
     vwc::Vector{SVector{N,T}} | "-"
@@ -1071,14 +1071,12 @@ 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] - sbm.ae_openw_l[i]
 
         # volumetric water content per soil layer and root zone
         vwc = sbm.vwc[i]

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 +94,12 @@ 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.runoff) ≈ 0.23657364759232993f0
+    @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