SWAP, a model to simulate transport of water, solutes and heat in unsaturated/saturated soils and crop growth

Submitted by joost.wolf on Tue, 04/12/2011 - 11:50
Program type
Soil dynamics and crop growth simulation model
Available since

SWAP simulates transport of water, solutes and heat in the vadose zone in interaction with vegetation development. The model employs the Richards equation including root water extraction to simulate soil moisture movement in variably saturated soils. Concepts are added to account for macroporous flow and water repellency. SWAP considers for solute transport the basic processes convection, dispersion, adsorption and decomposition. For more extensive studies which for instance include volatilization or nutrient transformations, SWAP generates soil water fluxes for detailed chemical transport models as PEARL for pesticides and ANIMO for nutrients. SWAP simulates soil heat flow taking into account actual heat capacities and thermal conductivities. The generic crop growth module WOFOST is incorporated to simulate leaf photosynthesis and crop growth. The soil moisture, heat and solute modules exchange status information each time step to account for all kind of interactions. Crop growth is affected by the actual soil moisture and salinity status on a daily basis. An extensive test protocol ensures the numerical code quality of SWAP.

For more information, see:



Scale of application
Spatial resolution
Key outputs

Total biomass, yield, evapo-transpiration, soil water flow, solute transport and heat transport in soil

Time horizon
Growth period
Time step of modeling
Required to run


Required to develop


Database I/O
text editor
Applications & Use

The SWAP model is suitable to select viable water management options, to perform regional studies employing geographical information systems, and to illustrate transport processes for education and extension. In recent years SWAP has been employed to explore alternative flow and transport concepts, to analyze laboratory and field experiments, and to evaluate management options with respect to field scale water and solute movement. Published, typical examples are given by Van Dam et al. (2008) for:

Field scale water and salinity management , Irrigation scheduling,  Transient drainage conditions,
Plant growth affected by water and salinity,  Pesticide leaching to ground water and surface water,
Regional drainage from top soils towards different surface water systems,  Optimization of surface water management,
Effects of soil heterogeneity,
SWAP also serves to generate soil water fluxes for pesticide and nutrient models. The model can be used to explore new flow and transport concepts for agro- and ecohydrology and on the analysis of laboratory and field experiments.

For more information, see the SWAP website:


Jos van Dam
Wageningen University Soil Physics, Ecohydrology and Groundwater Management Group, Droevendaalse steeg, Wageningen, The Netherlands