Preface

The ecohydrological model SWAP has a history of more than 50 years (Heinen et al. 2024). In 1974 R.A. (Reinder) Feddes and colleagues published a scientific paper on the numerical modelling of root water uptake in soils (Feddes et al. 1974). During it’s history regularly updates were spread with derived acronyms SWATRE, SWACROP, SWAP93, and SWAP: Feddes et al. (1978); Belmans et al. (1983); Wesseling et al. (1991); Kabat et al. (1992); Van den Broek et al. (1994); Van Dam et al. (1997); Kroes et al. (2001, 2017; 2003).

SWAP is used by researchers, engineers and students in the field of environmental science. Researchers employ the interactions between soil, water, plant and atmosphere as simulated by SWAP and the easy way in which the model can be adapted to specific research questions. Environmental engineers use the model as published and employ the practical boundary conditions of the model. In education SWAP is used to demonstrate typical transport situations in the biosphere. Students, ranging from Bachelor to PhD level, practice with the model. Some PhD students use SWAP as a research platform, to which they add innovative concepts.

At Wageningen University and Research (WUR) fundamental and applied research are closely entangled. Scientists and students of various environmental disciplines and from all continents collaborate intensively. This creates much synergy, of which SWAP is one of the products.

Since the last releases in 2017-2022 a large number of new ideas have been tested with SWAP. Currently in environmental research much attention is paid to the food-water-energy nexus. In this research interaction between soil hydrology and crop growth plays a key role. In WaterVision Agriculture (Hack–ten Broeke et al. 2016) (in Dutch: ‘Waterwijzer Landbouw’) we bring together the Dutch experience on how crop growth is affected by soil, climate and stresses due to lack of oxygen, lack of water or due to excess of salts. In the frame of WaterVision Agriculture we release this new SWAP version in which we implemented versatile improvements of recent years.

Our exciting journey does not end here. The future will bring new challenges. Therefore we supply SWAP with a well-structured source code and invite users to implement and test their own ideas. We very much appreciate feedback on the use of SWAP and suggestions for further improvements.

How to cite

Working Group SWAP. 2026. SWAP: theory and user guide; version 4.3.023. Wageningen Environmental Research, Wageningen, the Netherlands. Available at: https://swap.wur.nl/.

The SWAP team

Belmans, C., J. G. Wesseling, and R. A. Feddes. 1983. “Simulation of the Water Balance of a Cropped Soil: SWATRE.” Journal Article. Journal of Hydrology 63 (3-4): 271–86. https://doi.org/10.1016/0022-1694(83)90045-8.

Feddes, R. A., E. Bresler, and S. P. Neuman. 1974. “Field Test of a Modified Numerical Model for Water Uptake by Root Systems.” Journal Article. Water Resources Research 10: 1199–206. https://doi.org/10.1029/WR010i006p01199.

Feddes, R. A., P. J. Kowalik, and H. Zaradny. 1978. Simulation of Field Water Use and Crop Yield. Simulation Monographs. Book. Pudoc. Wageningen, The Netherlands.

Hack–ten Broeke, M. J. D., J. G. Kroes, R. P. Bartholomeus, et al. 2016. “Quantification of the Impact of Hydrology on Agricultural Production as a Result of Too Dry, Too Wet or Too Saline Conditions.” Journal Article. Soil 2: 391–402. https://doi.org/10.5194/soil-2-391-2016.

Heinen, M., M. Mulder, J. van Dam, et al. 2024. “SWAP 50 Years: Advances in Modelling Soil-Water-Atmosphere-Plant Interactions.” Journal Article. Agricultural Water Management 298. https://doi.org/10.1016/j.agwat.2024.108883.

Kabat, P., B. J. van den Broek, and R. A. Feddes. 1992. “SWACROP: A Water Management and Crop Production Simulation Model.” Journal Article. ICID Bulletin 41: 61–84.

Kroes, J. G., P. J. T. van Bakel, J. Huygen, and T. Kroon en R. Pastoors. 2001. Actualisatie van de Hydrologie Voor STONE 2.0. Rapport 298. Book. Alterra, Wageningen, The Netherlands.

Kroes, J. G., and J. C. van Dam. 2003. Reference Manual SWAP Version 3.03. Alterra Report 773. Book. Alterra, Wageningen, The Netherlands.

Kroes, J. G., J. C. van Dam, R. P. Bartholomeus, et al. 2017. SWAP Version 4; Theory Description and User Manual. Report 2780. Book. Wageningen Environmental Research, Wageningen, The Netehrlands. https://doi.org/10.18174/416321.

Van Dam, J. C., J. Huygen, J. G. Wesseling, et al. 1997. Theory of SWAP Version 2.0. Simulation of Water Flow, Solute Transport and Plant Growth in the Soil-Water-Atmosphere-Plant Environment. Technical Document 45. Book. Alterra, Wageningen, The Netherlands.

Van den Broek, B. J., J. C. van Dam, J. A. Elbers, et al. 1994. SWAP 1993, Input Instructions Manual. Report 45. Book. Department of Water Resources, Wageningen Agricultural University, Wageningen, The Netherlands.

Wesseling, J. G., J. A. Elbers, P. Kabat, and B. J. van den Broek. 1991. SWATRE; Instructions for Input. Internal Note,. Book. Winand Staring Centre, Wageningen, The Netherlands.