. SWAP version 4; Theory description and user manual. Wageningen, Wageningen Environmental Research, Report 2780. 244 pp.; 57 fig.; 17 tab.; 312 ref. SWAP 4 simulates transport of water, solutes and heat in the vadose zone. It describes a domain from the top of canopy into the groundwater which may be in interaction with a surface water system. The program has been developed by Wageningen Environmental Research and Wageningen University, and is designed to simulate transport processes at field scale and during entire growing seasons. This is a new release with recent developments on atmosphere, soil water and crop growth interactions.This manual describes the theoretical background, model use, input requirements and output tables. • Acquisition, duplication and transmission of this publication is permitted with clear acknowledgement of the source.• Acquisition, duplication and transmission is not permitted for commercial purposes and/or monetary gain.• Acquisition, duplication and transmission is not permitted of any parts of this publication for which the copyrights clearly rest with other parties and/or are reserved.Wageningen Environmental Research assumes no liability for any losses resulting from the use of the research results or recommendations in this report. Wageningen Environmental Research Report 2780 | ISSN 1566-7197Photo cover: The picture on the front cover shows SWAP's core processes in the soil below a grass vegetation positioned in a rural area with different land uses. ContentsPreface 7 and hence the dynamics of light interception. During crop development a part of the living biomass dies due to senescence (Chapter 7).Grass growth is special: it is perennial, very sensitive to nitrogen, and grass is either grazed or mowed. Therefore SWAP includes a separate WOFOST module for grass, which simulates these special grass features (Chapter 7).SWAP simulates transport of salts, pesticides and other solutes that can be described with basic physical relations: convection, diffusion, dispersion, root uptake, Freundlich adsorption and first order decomposition. In case of advanced pesticide transport, including volatilization and kinetic adsorption, SWAP can be used in combination with PEARL. In case of advanced transport of nitrogen and phosphorus, SWAP can be used in combination with ANIMO or Soil-N (Chapter 8).SWAP may simulate soil temperature analytically, using an input sine function at the soil surface and the soil thermal diffusivity. In the numerical approach, SWAP takes into account the influence of soil moisture on soil heat capacity and soil thermal conductivity. The top boundary condition may include air temperatures or soil surface temperatures (Chapter 9).The snow module calculates the accumulation and melting of a snowpack when the air temperature is below a threshold value. The water balance of the snow pack includes storage, incoming snow and rain and outgoing melting and sublimation. Melting may occur due to air temperature rise or heat release from rainfall. When a snowpack is p...

• Acquisition, duplication and transmission of this publication is permitted with clear acknowledgement of the source.• Acquisition, duplication and transmission is not permitted for commercial purposes and/or monetary gain.• Acquisition, duplication and transmission is not permitted of any parts of this publication for which the copyrights clearly rest with other parties and/or are reserved.Wageningen Environmental Research assumes no liability for any losses resulting from the use of the research results or recommendations in this report. such as transformation in water and in sediment, volatilization from the water layer and transport in the water layer and in sediment by advection, dispersion and diffusion. Several processes describing the fate of the active ingredient depend on the temperature. Until now the change of temperature was described in a simple way by using monthly averaged temperatures. The temperature of the sediment equated the temperature of the water layer. This description of the temperature does not consider the daily change of the temperature in the water layer, and neither the change in daily average during the month. The concepts for describing the temperature in the water layer and in the sediment were improved, enabling enhanced incorporation of the effect of temperature on exposure concentrations.The improved description of the temperature in the water layer is based on quantification of contributions of all relevant terms of the energy budget of the water system. These terms are incoming and outgoing shortwave and longwave radiation, sensible and latent heat exchange between air and water, precipitation, potential heat exchange between water and sediment and external sources, such as incoming drainage water. In this improved temperature concept it is assumed that the water layer is perfectly mixed, hence the temperature is constant for each time horizontally and vertically in the entire water layer. The temperature of sediment is assumed equal to the water temperature. The improved temperature model then comprises a 1D bulk model.The improved concept for temperature in TOXSWA was tested using an existing model implementation of the 1D bulk model. De temperatures calculated by TOXSWA agreed well with temperatures determined with the 1D bulk model.The effect of use of the improved temperature module was evaluated by executing calculations of the TOXSWA model using the two options, i.e. the option of the 1-D bulk model as well as the option of the monthly averaged temperatures. Notable differences were calculated for the impact on transformation and volatilization. Depending on the change of temperature in the month using the improved concept of temperature can result in higher or lower exposure concentrations.The improved description of the effect of temperature on diffusion not only considered the improved description of the temperature as a function of time, but also the introduction of dependency of the diffusion coefficient on temperature. Test calculations showed that introduct...

Both in land evaluation and in water management quantitative methods, GIS and simulation modelling are well-known techniques for quantifying the effects of changes, such as land use or climate change.For hydrological management decisions information is often required on the effect of those decisions on agricultural production. To serve the needs of different types of users, like water authorities, provinces, drinking water companies and the National Department of Infrastructure and Water Management we developed a toolbox named WaterVision Agriculture as an instrument that can determine effects on crop yield and the farm economy as a result of drought, too wet or too saline conditions for both current and future climatic conditions. WaterVision Agriculture is based on the hydrological simulation model SWAP, the crop growth model WOFOST and farm management and economic assessments such as DairyWise for dairy farming. The WaterVision Agriculture (WVA) project resulted in two products, namely i) an easily applicable tool (also called the WVA-table) and ii) the operational models for hydrology and crop growth SWAP and WOFOST for calculating effects on field scale combined with calculating farm economic results and indirect effects. SWAP simulates water transport in the unsaturated zone using meteorological data, boundary conditions (like groundwater level or drainage) and soil parameters. WOFOST simulates crop growth as a function of meteorological conditions and crop parameters. Using the combination of these process-based models and methods for describing crop management and economic value we derived a meta-model, i.e. a set of easily applicable simplified relations for assessing crop growth as a function of 3 soil type and groundwater level. These relations are based on multiple model runs for at least 72 soil units and the possible groundwater regimes in the Netherlands. The easily applicable tool (WVA-table) uses this meta-model.Applying the meta-model of WaterVision Agriculture should allow for better decisions on land use or soil and water management because the instrument can help to quantify the effects of changes in climate, land use, hydrological conditions or combinations of these effects on agricultural production.

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