Modelling tool capability overview

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A set of commonly used modelling tools in South Africa was reviewed for the WRC “Critical catchment model inter-comparison and model use guidance development” project. This set included major tools developed in South Africa: ACRU and the Pitman model-based tools, WRSM-Pitman and SPATSIM-Pitman. It also included two tools that were developed in the northern hemisphere, but have been used in South Africa and globally: SWAT and MIKE-SHE. Locally developed tools can have certain advantages from being designed with the South African context in mind, both in terms of local data availability and in terms of local climate characteristics, ecosystems, soils, geologic types, and land and water management practices (e.g. landscapes with many small farm dams). SWAT and MIKE-SHE have resourced development teams behind them that continually update the tools and adapt them to make use of developing globally available data sources, such as remotely sensed data, and generally improved access to greater computing power. This suite of tools covers a diversity of model structure and algorithm type options, but users should be aware there are many many tools available (see more examples)

The tables below summarise basic information about the tools in this set:

  • tool background & versions covered here
  • intended uses of the tool & development focuses
  • broad model structural characteristics across tools
  • overview of modelling capabilities across tools


These tables provide an overview. More detailed information about the structural options and capabilities of the tools is given across the other inter-comparison pages.

Tool background & intended uses

Modelling software tool background & version covered
Characteristic WRSM-Pitman SPATSIM-Pitman ACRU SWAT MIKE-SHE
Developed in South Africa yes yes yes no no
Current curator / developer Bailey & Pitman Water Resources Ltd Rhodes University, Institute of Water Resources (IWR) University of KwaZulu Natal, Centre for Water Resources Research (UKZN-CWRR) Texas A&M University & US Department of Agriculture (USDA) Danish Hydrologic Institute (DHI)
Free to access yes yes yes yes no*

free student licenses & free/reduced research licenses by arrangement

Version reviewed in wiki WRSM-Pitman version 2.9 SPATSIM GWv3 Global Options Threaded model ACRU 4 SWAT & ArcSWAT 2012 MIKE-SHE & MIKE Hydro River, version 2019 & 2020
Reference documents consulted

(see documentation links page)

Theory manual:

Bailey, A.K. (2015). WRSM2000/Pitman: Water Resources Simulation Model for Windows - Theory Manual (Water Research Commission).

User manual:

Bailey, A.K., and Pitman, W.V. (2016). WRSM/Pitman User’s Manual: WR2012 Volume 7 (Water Research Commission).

Theory documentation:

Hughes, D.A. (2004). Incorporating groundwater recharge and discharge functions into an existing monthly rainfall–runoff model. Hydrological Sciences Journal 49.

Hughes, D.A. (2013). A review of 40 years of hydrological science and practice in southern Africa using the Pitman rainfall-runoff model. Journal of Hydrology 501, 111–124.

Kapangaziwiri, E. (2007). Revised parameter estimation methods for the Pitman monthly rainfall-runoff model. MSc. Rhodes University.

User manual:

Hughes, D.A. (2019). SPATSIM v3 & IWR version of the Pitman model (IWR Rhodes University).

Theory manual:

Schulze, R.E. (1995). Hydrology and Agrohydrology: A Text to Accompany the ACRU 3.00 Agrohydrological Modelling System (Water Research Commission).

User manuals:

Clark, D.J., Smithers, J.C., Thornton-Dibb, S.L.C., and Lutchminarian, A. (2012). ACRU 4 User Manual: User Interface & Tutorials (Volume 3 of Deployment, Maintenance, & Further Development of SPATSIM-HDSF)

Schulze, R.E., and Davis, N.S. (2018). Practitioners’ Handbook for Undertaking Current and Projected Future Climate Related Risk and Vulnerability Modelling Assessments (an update of the ACRU user manual) (Schulze and Associates).

Theory manual:

Neitsch, S.L., Arnold, J.G., Kiniry, J.R., and Williams, J.R. (2011). Soil and Water Assessment Tool (SWAT) Theoretical Documentation, Version 2009 (Texas Water Resources Institute, Texas A&M University).

User manuals:

Winchell, M., Srinivasan, R., Di Luzio, J., and Arnold, J. (2013). ArcSWAT Interface for SWAT2012: User’s Guide (Texas Water Resources Institute, Texas A&M University).

Arnold, J.G., Kiniry, J.R., Srinivasan, R., Williams, J.R., Haney, E.B., and Neitsch, S.L. (2012). Soil & Water Assessment Tool (SWAT) - Input/Output Documentation, Version 2012 (Texas Water Resources Institute, Texas A&M University).

Theory manuals:

DHI (2019). MIKE SHE Manual, Volume 2: Reference Guide, MIKE 2019 (Danish Hydrologic Institute).

DHI (2019). MIKE 1D: DHI Simulaton Engine for 1D river and urban modelling - Reference Manual, MIKE 2019 (Danish Hydrologic Institute).

User manuals:

DHI (2019). MIKE SHE Manual, Volume 1: User Guide, MIKE 2019 (Danish Hydrologic Institute).

DHI (2019). MIKE Hydro River: User Guide, MIKE 2019 (Danish Hydrologic Institute).


These software tools have different development histories and somewhat different focuses, however all have adapted over time, adding features that allow them to be used in more contexts and have generally overlapping intended applications (see table below). The structural options and design of each tool will reflect the intended applications as well as the balance struck by the developers between potentially competing concerns and goals, such as achieving parsimony, including detailed representation of land cover differences to estimate the impacts of change, maintaining ease of use of the tool, facilitating quantification of model output uncertainty, ensuring applicability in data limited contexts, etc. For these reasons, despite the overlap in general intended uses, the tools offer some fairly different modelling strategies (see structure overview below). This impacts how they can be applied in specific settings (as documented in more detail here). For example, all the tools are capable of modelling the impacts of land use change to some degree, however WRSM-Pitman and SPATSIM-Pitman place greater limitations on the number and types of land cover that can be explicitly modelled compared to the other tools. A summary table of some key modelling capabilities across the tools is presented below.

Intended uses & development focuses summary
Characteristic WRSM-Pitman SPATSIM-Pitman ACRU4 SWAT2012 MIKE-SHE
Specific tool development focuses
  • Flexible network for managed systems with transfers,
  • Irrigated area representation
  • IAP & plantation forestry water use
  • Groundwater-surface water interaction (vegetation & GW pumping impacts)
  • Parsimony,
  • Uncertainty assessment & stochastic modelling,
  • Groundwater-surface water interaction (vegetation & GW pumping impacts)
  • Detailed land cover type representation,
  • Crop & irrigation detail,
  • IAP & plantation forestry water use, including deep rooted vegetation in riparian areas
  • Detailed land cover type representation,
  • Crop & irrigation detail,
  • Coupling to GIS tools
  • Spatial discretisation & distribution (climate, land cover, soil, geology, etc), fine scale processes,
  • Groundwater-surface water interaction,
  • Coupled hydraulic channel model & flooding processes
Intended applications:
Water balance estimation yes yes yes yes yes
Design hydrology & flood analyses no no yes yes yes
Supply planning (general) yes yes yes yes yes
Reservoir yield yes yes yes yes yes
Irrigation planning yes limited yes yes yes
Groundwater recharge yes yes yes yes yes
GW-SW interactions & GW pumping impacts yes yes no yes yes
Land cover change impacts yes yes yes yes yes
Climate change impacts yes yes yes yes yes
Application limitations
  • Monthly model: not applicable for peak flow, flood assessment, design hydrology
  • No irrigation direct from groundwater
  • Monthly model: not applicable for peak flow, flood assessment, design hydrology
  • No irrigation direct from groundwater
  • Simplified groundwater modelling;
  • Does not model groundwater pumping
  • Highly simplified deep groundwater modelling
(None documented for the modelling system as whole, only for certain process options within it. The learning curve for its use and computing power required can pose a practical limitation to its application )


Model structure & capabilities overview across tools

The table below gives a very basic overview of the type of model structure that can be built in each tool. More details about the model structure options across tools are presented here.

Model spatial & temporal scale overview by tool
Characteristic WRSM-Pitman SPATSIM-Pitman ACRU4 SWAT2012 MIKE-SHE
Intended scale of catchment or modelled area Local to regional:

no suggested min-max model size

Local to regional:

10-10,000’s of km2 

more typical: 100-1,000’s km2

Field to regional:

no suggested min-max model size

Field to regional:

no suggested min-max model size

Field to regional:

no suggested min-max model size

Timestep Monthly*


A daily version has been developed. Limited use to-date.

Monthly*


A daily version has been developed. Limited use to-date

Daily Daily, subdaily Daily, subdaily*


Calculation timesteps are dynamic and vary by process. All outputs saved for the same use-selected step.

Spatial discretisation (model spatial units) Modules connected by routes


(“runoff” modules + special area modules + channel modules create subcatchments)

Subcatchments + limited internal sub-area types HRUs within subcatchments HRUs within subcatchments Grid cells (3D),

with optional calculation simplifications: surface flow modelled for zones, interflow & groundwater modelled for storage reservoirs within subcatchments.

Suggested model unit scales Runoff module:  < 1,000 km2 (none listed) Subcatchments: 5-50 km2

HRUs:  < 30km2

(none listed) (none listed)

Despite having largely overlapping intended uses in general, there is notable diversity in model structure (table above) and across the sets of modelling capabilities in this set of tools (table below). Some key points arising from the capabilities comparison are:

  • No one tool had all the capabilities listed.  All the tools have differing sets of advantages over the others.
  • Although both based on the same predecessor model structure and sharing many basic process algorithms, WRSM-Pitman and SPATSIM Pitman have diverged in capabilities across several aspects. These differences are linked to WRSM’s modular network structure compared to the SPATSIM version’s focus on the subcatchment as the primary unit for process representation. For example, a WRSM model can include user-defined artificial water transfers between channel units in a model network, which SPATSIM does not include.
  • Only MIKE-SHE has a fully coupled hydraulic model, allowing it to model channel-floodplain interactions in more detail. Other tools can represent some aspects of overbank flooding and the fate of the flood water, but only for their wetland modules.
Model tool capabilities summary
General term WRSM-Pitman SPATSIM-Pitman ACRU4 SWAT2012 MIKE-SHE
Climate (rain & PET)
Spatially variable across model domain yes yes yes yes yes
Spatially variable within subcatchment (limited) no yes no yes
Inter-annual variability in PET no yes yes yes yes
Land cover & change
Processes explicitly linked to land cover (limited) (limited) yes yes yes
Multiple land cover types included (limited) (limited) yes yes yes
Cover has explicit location in subcatchment (limited) no (limited) (limited) yes
Cover can vary over model run timespan yes no (limited) no (limited)
Irrigation + dynamic demand & supply yes yes yes yes yes
Potential direct ET from GW (deep root) yes yes (limited) (limited) yes
Peak flows & flooding
Max daily or subdaily peak flow est. no no yes yes yes
Explicit impacts of channel capacity on flow (limited) (limited) (limited) (limited) yes
Calculation of flooded area extent (limited) no (limited) (limited) yes
Flood water subject to infiltration, ET, etc (limited) no yes no yes
Reservoirs, dams & channel flow modification
Reservoirs explicitly modelled yes yes yes yes yes
Facility to represent many small dams no yes yes (limited) no
Abstractions & external inputs yes yes yes yes yes
Internal transfers between model units yes no yes yes (limited)
GW representation & GW-SW interactions
Dynamic, 2-way, GW-SW exchange yes yes no yes yes
GW table elevation predicted (limited) (limited) no (limited) yes
GW pumping included yes yes no yes yes
Wetlands & riparian zones
Wetland processes included yes yes yes yes yes
On-channel wetlands yes yes yes yes yes
Off-channel wetlands (fed by channel spill) yes yes yes no yes
GW fed (receive GW from surrounding) (limited) (limited) (limited) (limited) yes
Other catchment & vegetation processes
Sediment movement no no yes yes yes
Water quality no no yes yes yes
Crop yield no no yes yes no
Uncertainty & parameter calibration
In-built tools for uncertainty, parameter sensitivity, & auto-calibration (batch runs) no yes no no yes