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.

Modelling software tools: 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).

Basic model structures by tool

Characteristic	WRSM-Pitman	SPATSIM-Pitman	ACRU4	SWAT	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)

Tool intended uses & development focuses summary

Characteristic	WRSM-Pitman	SPATSIM-Pitman	ACRU	SWAT	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
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	Highly simplified groundwater modelling; Does not model groundwater pumping	Highly simplified deep groundwater modelling	(None documented for system as whole, only for certain process options within it.)
Intended applications