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 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 overseas, but have been used across various contexts globally, SWAT and MIKE-SHE. Locally developed modelling tools can have certain advantages from being designed with the South African context in mind, in terms of local 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 help to continually update the tools and adapt them to make use of developing globally available data sources, such as remote sensing data and linked products, 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 these tools: 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.

Background & basic characteristics of reviewed modelling tools
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

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
  • Flexible network for tracking managed system transfers,
  • GW-SW interaction,
  • IAP & plantation forestry water use
  • Parsimony,
  • Uncertainty assessment,
  • GW-SW interactions
  • Land cover type representation,
  • Crop & irrigation detail,
  • IAP & plantation forestry water use
  • Land cover type representation,
  • Crop & irrigation detail,
  • Coupling to GIS tools
  • Spatial discretisation & fine scale processes,
  • GW-SW interaction,
  • Coupled hydraulic channel model with overbank flood process representation


Modelling tool capabilities overview
Capability WRSM-Pitman SPATSIM-Pitman ACRU SWAT 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