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 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

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