Process representation across tools

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building process representation overview tables + links to more specific pages about individual processes

Canopy interception and evaporation (vs throughfall)

Algorithm description	WRSM-Pitman	SPATSIM-Pitman	ACRU4	SWAT2012	MIKE-SHE, semi-distributed & fully distributed
Algorithm inputs (input data, parameters, model-calculated states/storages)	Rain Cover properties: max interception	Rain Cover properties: max interception	Rain PET Canopy storage (state) Cover properties: max interception (OR LAI)	Canopy interception is not explicitly modelled when using daily timestep modelling. It is implicitly considered in the ‘initial abstraction’, see infiltration & surface runoff below	Rain PET Canopy storage (state) Cover properties: LAI canopy interception coefficient
Function type	exponential & threshold	exponential & threshold	threshold		threshold
Thresholds	yes: timestep interception capacity (calculated)	yes: timestep interception capacity (calculated)	yes: timestep interception capacity (calculated)		yes: timestep interception capacity (calculated)

Infiltration into soil moisture (vs surface runoff or surface ponding)

Note: This excludes the case of a modelling unit (HRU, grid cell, area within a subcatchment, etc.) is designated as impervious. In this case, rain inputs would become surface runoff, potentially with a portion staying behind as surface storage/ponding if the area has attenuation specified (to represent roughness and flatness).

Algorithm description	WRSM-Pitman	SPATSIM-Pitman	ACRU4	SWAT2012	MIKE-SHE, semi-distributed, more conceptual	MIKE-SHE, fully-distributed, more physical
Algorithm inputs (input data, parameters, model-calculated states/storages)	Rain Rainfall distribution factor Soil moisture (state) Soil properties: Saturation soil moisture Infiltration rate distribution (min, max)	Rain Rainfall distribution factor Soil moisture (state) Soil properties: Saturation soil moisture Infiltration rate distribution (min, max)	Throughfall (rain-interception) Soil moisture within "infiltration depth"(state) Soil properties: Saturation soil moisture "Infiltration depth" parameter Macropore by-pass (clay cracking)	Throughfall (rain-interception) Soil moisture (state) Soil properties: Saturation soil moisture Curve number (SCS-CN) Macropore by-pass	Throughfall (rain-interception) Soil moisture (state) Soil properties: Saturation soil moisture Saturated hydraulic conductivity (Ksat), Macropore by-pass	Throughfall (rain-interception) Soil moisture (state) Soil properties: Saturation soil moisture Soil moisture retention curve Saturated hydraulic conductivity (Ksat), Macropore by-pass
Function type	non-linear & threshold	non-linear & threshold	power & threshold	power & threshold	linear (rate) & threshold	non-linear & threshold
Thresholds	yes: Max infiltration rate, Saturation soil moisture* *Saturation excess becomes interflow, not surface runoff	yes: Max infiltration rate, Saturation soil moisture* *Saturation excess becomes interflow, not surface runoff	yes: Saturation soil moisture* *Fraction of saturation excess becomes "delayed flow"~interflow, not "quickflow"~surface runoff	yes: Max infiltration rate (calculated), Saturation soil moisture	yes: Max infiltration rate (uses Ksat), Saturation soil moisture	yes: Max infiltration rate (calculated), Saturation soil moisture

Surface runoff to channel network

Note on surface runoff vs ponding and surface storage: Water reaching the land surface which does not infiltrate into soil in a timestep, will either become surface runoff or remain as surface ponding/surface storage. In some models (e.g. Pitman models) all water that does not infiltrate becomes surface runoff. This makes sense when the timestep is long (e.g. a month). If the model represents surface storage, then in subsequent model timesteps this water can evaporate, infiltrate, and/or become surface runoff in the next timestep. Some models have relatively short timesteps (subdaily, daily) compared to the rate at which water would move across a modelled land unit (which could be large, rough, and/or flat, slowing the flow rate), explaining why some water will be considered 'surface storage' in one timestep and then 'surface runoff' in the next timestep in the model. MIKE-SHE can also consider that land surfaces can be very rough, or have dips that trap water, and so some amount surface water will not be able to runoff at all, regardless of a time delay. This water will both evaporate and infiltrate over time.

Algorithm description	WRSM-Pitman	SPATSIM-Pitman	ACRU4	SWAT2012	MIKE-SHE, semi-distributed, more conceptual	MIKE-SHE, fully-distributed, more physical
Algorithm inputs (input data, parameters, model-calculated states/storages)	Surface water present* (state) *Month timestep: all water not infiltrating becomes runoff	Surface water present* (state) *Month timestep: all water not infiltrating becomes runoff	Surface water present* (state) Lag coefficient* *Lag coefficient separates "quickflow"~surface runoff from "delayed-flow"~interflow. Quickflow portion reaches the channel on the same day generated (rain day). The rest is lagged over subsequent days	Surface water present* (state) Surface path properties: Path length Path slope Path roughness (Manning's n)	Surface water present* (state) Surface path properties: Detention storage Path length Path slope Path roughness (Manning's n)	Surface water present* (state) Surface path properties: Detention storage Path length (from gridded topography) Path slope(from gridded topography) Path roughness (Manning's n)
Function type	(no transformation)	(no transformation)	(no transformation)	non-linear	non-linear & threshold	non-linear & threshold
Thresholds	no* *none after infiltration has been calculated	no* *none after infiltration has been calculated	no* *none after infiltration has been calculated	no* *none after infiltration has been calculated	yes: Detention storage	yes: Detention storage

Evapotranspiration (ET) from soil moisture (SM)

Note: More coverage of evapotranspiration related terminology and inputs across different tools can be found here

Algorithm description	WRSM-Pitman	SPATSIM-Pitman	ACRU4	SWAT2012	MIKE-SHE, semi-distributed, more conceptual	MIKE-SHE, fully-distributed, more physical
Algorithm inputs (input data, parameters, model-calculated states/storages)	S-Pan evaporation Soil moisture (state) Vegetation properties: "Crop" coefficient (vs pan) Pitman ET coefficient* Soil properties: Saturation soil moisture *determines linear decline of ET with soil moisture decline	S-Pan evaporation Soil moisture (state) Vegetation properties: "Crop" coefficient (vs pan) Pitman ET coefficient* Soil properties: Saturation soil moisture *determines linear decline of ET with soil moisture decline	A-Pan evaporation Soil moisture (state) Vegetation properties: "Crop" coefficient (vs pan) Root depth distribution Soil properties: Saturation soil moisture* Field capacity SM Wilting point SM *ET assumed to also decline if soil gets close to saturation, waterlogging, unless wetland plants	Remaining ET demand (PET - Canopy evap.) Soil moisture (state) Vegetation properties: LAI Root depth (max) Root distribution Demand redistribution coefficient Soil properties: Field capacity SM Wilting point SM	Remaining ET demand (PET - Canopy evap. - Ponded evap.) Soil moisture (state) Vegetation properties: "Crop" coefficient ET curtailment SM Root depth (max) Root distribution Soil properties: Field capacity SM Wilting point SM	Remaining ET demand (PET - Canopy evap. - Ponded evap.) Soil moisture (state) Vegetation properties: "Crop" coefficient ET vs SM curve parameter Root depth (max) Root distribution ET demand depth distribution Soil properties: Soil moisture retention curve
Function type	linear & threshold	linear & threshold	multi-part linear & threshold	non-linear & threshold	multi-part linear & threshold	non-linear & threshold
Thresholds	yes: ET demand, Wilting point SM	yes: ET demand, Wilting point SM	yes: ET demand, Wilting point SM	yes: yes: ET demand, Wilting point SM	yes: ET demand, Wilting point SM	yes: ET demand, Wilting point SM

Evapotranspiration (ET) from groundwater (GW)

Note: More coverage of evapotranspiration related terminology and inputs across different tools can be found here

Algorithm description	WRSM-Pitman (Sami GW)	SPATSIM-Pitman (Hughes GW)	ACRU4	SWAT2012	MIKE-SHE, semi-distributed, more conceptual	MIKE-SHE, fully-distributed, more physical
Algorithm inputs (input data, parameters, model-calculated states/storages)	riparian area only A-Pan evaporation Riparian area Aquifer storage (state) Vegetation properties: "Crop" coefficient (vs pan) Aquifer properties: Aquifer storage limit for ET	riparian area only Remaining ET demand (PET - ET from soil) Riparian area Aquifer storage (state) Vegetation properties: "Crop" coefficient (vs pan) Pitman ET coefficient* Aquifer properties: Aquifer storage limit for ET	riparian area only Indirect representation: Specified riparian zone HRU can receive a user-specified fraction of the aquifer outflow from connected upslope HRUs. This water is added to riparian HRU soil in the B-horizon, where it can be accessed for ET and can recharge GW. No ET (or capillary rise) is simulated from the GW store of the riparian HRU.	represented through capillary rise into the soil driven by ET demand PET Aquifer storage (state) Soil properties: Capillary rise rate coefficient Aquifer properties: Aquifer storage limit for capillary rise + all inputs for ET from soil	riparian area only represented through capillary rise into the soil driven by ET demand Remaining ET demand (PET - Canopy evap. - Ponded evap. - ET from soil) Aquifer storage (state) Aquifer properties: Aquifer storage limit for capillary rise + all inputs for ET from soil	capillary rise is calculated, but roots can also extend below the water table and withdraw directly Remaining ET demand (PET - Canopy evap. - Ponded evap. - ET from soil) Water table depth (state) Aquifer properties: Saturated hydraulic conductivity (Ksat) + vegetation property inputs for ET from soil
Function type	non-linear & threshold	non-linear & threshold		non-linear & threshold	non-linear & threshold	non-linear & threshold
Thresholds	yes: ET demand, Aquifer storage limit for ET	yes: ET demand, Aquifer storage limit for ET		yes: ET demand, Aquifer storage limit for capillary rise	yes: ET demand, Aquifer storage limit for capillary rise	yes: ET demand, Water table depth vs root depth