This chapter shows how the methods discussed in the previous chapters are applied in hydrological and meteorological models. The SWAP (Soil, Water, Atmosphere, Plant) model is an example of a field-scale ecohydrological model (Section 9.1). In Section 9.2 various aspects of land–surface models as used in weather and climate models are discussed.

Introduction

SWAP simulates transport of water, solutes and heat in the vadose zone (Kroes et al., 2008; Van Dam et al., 2008). The model includes vegetation growth, as affected by meteorological and hydrological conditions. The upper boundary of the model domain is a plane just above the canopy. The lower boundary corresponds to a plane in the shallow groundwater (Figure 9.1). In this model domain the transport processes are predominantly vertical; therefore SWAP is a one-dimensional, vertical directed model. The flow below the groundwater level may include lateral drainage fluxes, provided that these fluxes can be prescribed with analytical drainage formulas. The model is very flexible with regard to input data at the upper and lower boundaries. At the top general data on rainfall, irrigation and evapotranspiration are used. For frost conditions a simple snow storage module has been implemented and soil water flow will be impeded when soil temperature descends below zero. To facilitate temporal detailed studies on surface runoff and diurnal transpiration fluxes, evapotranspiration and rainfall data can be specified at daily and shorter time intervals. At the model lower boundary, various forms of head and flux based conditions are used.