Modelling tool capability overview
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
| 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 | 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.
| Characteristic | WRSM-Pitman | SPATSIM-Pitman | ACRU4 | SWAT2012 | MIKE-SHE |
|---|---|---|---|---|---|
| Specific tool development focuses |
|
|
|
|
|
| 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 |
|
|
|
|
(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.
| 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*
|
Monthly*
|
Daily | Daily, subdaily | Daily, subdaily*
|
| Spatial discretisation (model spatial units) | Modules connected by routes
|
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.
| 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 |