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 the major tools developed in South Africa, ACRU and the Pitman model-based tools (WRSM-Pitman and SPATSIM-Pitman), as well as two tools that were developed in the northern hemisphere, but have been used globally, SWAT and MIKE-SHE. Locally developed modelling tools can have certain advantages from being designed with the South African context in mind, both in terms of data availability and local climate characteristics, ecosystems, soils and geologic types, as well as land and water management practices. 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.
The two tables below summarise basic information about the tools in this set: the first gives intended uses and broad structural characteristics and the second gives an overview of modelling capabilities across the tools that are likely to be in demand for many typical use-cases.
| 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 access | yes | yes | yes | yes | no |
| Version reviewed | WRSM-Pitman version 2.9 | SPATSIM GWv3 Global Options Threaded model | ACRU 4 | SWAT & ArcSWAT 2012 | MIKE-SHE & MIKE Hydro River, version 2017 |
| Reference documents | Theory manual: (Bailey, 2015);
User manual: (Bailey and Pitman, 2016) |
Theory papers: (Hughes, 2004, 2013; Kapangaziwiri, 2007);
User manual: (Hughes, 2019) |
Theory manual: (Schulze, 1995);
User manuals: (Clark et al., 2012; Schulze and Davis, 2018) |
Theory manual: (Neitsch et al., 2011);
User manuals: (Arnold et al., 2012) |
Theory manuals:(DHI, 2017a, 2017b);
User’s manuals:(DHI, 2017d, 2017c) |
| Intended spatial scale
(catchment or model 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 |
| Spatial discretisation | Modules ('runoff' modules/subcatchments,
special sub-areas, channels, reservoirs) linked by routes |
Subcatchments + limited internal sub-area types | HRUs within subcatchments | HRUs within subcatchments | Fully distributed (gridded)
OR combinations of grids and zones for different process calculations within subcatchments (if all process zones align, would act like HRUs) |
| Intended subcat size < 1,000 km2 | Intended subcat size 5-50 km2;
HRU size < 30km2 |
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| Timestep | Monthly* | Monthly* | Daily | Daily, sub-daily | Daily, sub-daily
(dynamic timestep length, can vary across processes) |
| Intended modelling applications (as documented): | |||||
| Water balance estimation | yes | yes | yes | yes | yes |
| Design hydrology (flood peaks) | yes | yes | yes | ||
| Supply planning (general) | yes | yes | yes | yes | yes |
| Reservoir yield | yes | yes | yes | yes | yes |
| Irrigation planning | yes | yes | yes | yes | |
| Groundwater recharge | yes | yes | yes | yes | yes |
| Groundwater-surface water (GW-SW) interactions & pumping impacts | yes | yes | yes | ||
| Land cover change impacts | yes | yes | yes | yes | yes |
| Climate change impacts | yes | yes | yes | yes | yes |
| Application limitations (as documented) | Not for peak flow, flood assessment, or design hydrology | Not for peak flow, flood assessment, design hydrology | Not represent deep GW processes - not for GW pumping impact | Not represent deep GW processes | (None listed for the modelling system
as whole, only for certain process representation options.) |
| Specific development focuses particular to tool |
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The table below gives an overview of a range of capabilities of the modelling tools under review. This summary is supported by more detailed comparison of the structural and process algorithm differences between the modelling tools. Comparing the capabilities of a modelling tool to the needs of a modelling exercise is a critical step in tool selection. When a modelling tool lacks a capability that would be desirable, but not critical for the exercise, there may be ways to adapt the model set-up to account for this, such as adjusting parameter values for implicit representation of a feature or process the tool does not include explicitly.
| Capability | WRSM-Pitman | SPATSIM-Pitman | ACRU | SWAT | MIKE-SHE |
|---|---|---|---|---|---|
| Climate (rain & ET demand) | |||||
| Spatially variable across model domain | yes | yes | yes | yes | yes |
| Spatially variable within subcatchment | (limited) | no | yes | no | yes |
| Inter-annual variability in ET demand | 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 |
| components of the catchment and concept of a subcatchment
affects how the river is defined and the location of the outlet | |||
| semi-distributed subcatchments, each with an outlet
streamflow is directed to a particular channel unit (or catchment outlet)
semi-distributed land units |
land areas (modules) draining into a river network,
streamflow estimates available at each module outlet lumped land units |
flow paths defined by the topography and material of individual land units/cells
streamflow estimated at each cell and between cells and vertical units
distributed land units | |
| SPATSIM-Pitman
ACRU SWAT |
WRSM-Pitman | MIKE-SHE | |
| scale of representation
affects how the process is calculated and the meaning of parameter values | |||
| subcatchment | HRU | grid cell | |
| ACRU
SPATSIM-Pitman WRSM-Pitman |
SWAT
ACRU MIKE-SHE |
MIKE-SHE | |
| land cover type discretisation and representation
affects whether the land cover is explicitly represented and the ability to pinpoint/track specific impacts of a land cover type on the water balance | |||
| no restrictions
explicitly represents multiple land uses |
considerable restrictions
does not fully represent multiple land uses | ||
| ACRU
MIKE-SHE SWAT WRSM-Pitman |
SPATSIM-Pitman | ||
| connections between landscape units
affects the flow of water between land units before reaching the outlet | |||
| outflows routed to the catchment
(i.e. subcatchment units to catchment outlet) |
interaction of flow between subcatchments
(i.e. subcatchment to subcatchment interactions then routing to catchment outlet) | ||
| ACRU (unless a riparian zone is added)
SWAT |
SPATSIM-Pitman
WRSM-Pitman MIKE SHE | ||
| aquifer representation and connectivity
determines the spatial scale of groundwater flows | |||
| subcatchment scale | HRU scale | 3D modelling mesh
(user-defined grid cells) | |
| no regional aquifer water exchanges between subcatchments | no flow between subcatchments | all units can interact | |
| distributed MIKE-SHE
SWAT SPATSIM-Pitman WRSM-Pitman |
ACRU (with the exception of version 3) | distributed MIKE-SHE | |
| No channel transmission | Channel transmission
(contributes and redistributes water to the unsaturated zone, not the aquifer) | ||
| ACRU
MIKE-SHE SPATSIM-Pitman WRSM-Pitman |
SWAT | ||
| channel representation and connectivity
affects the interactions with the channel network | |||
| hydrodynamic model with limited hydraulic features
less options and opportunities for interactions with the channel network |
full hydraulic model
more options and opportunities for interactions with the channel network (trade off: increases model complexity, computational demands, and run-times) | ||
| ACRU
SWAT SPATSIM-Pitman WRSM-Pitman |
SWAT | ||
| reservoir representation and connectivity
affects the setup demand & accessibility of water storage for irrigation and inflows into the storage | |||
| Can include farm dams within a subcatchment
(practical and useful feature in some landscapes) |
Implied reservoir within the catchment
an internal water storage unit (ponds) are used to imply reservoirs, ponds cannot be used as a water supply for irrigation, ponds can act as flood control structures with outflow rules |
Does not include farm dams within a subcatchment
| |
| ACRU
SPATSIM-Pitman WRSM-Pitman |
SWAT | MIKE SHE | |