Integrated Models in Hydrology and Meteorology - Transport in the Atmosphere-Vegetation-Soil Continuum - page 302

9
Integrated Models in Hydrology and Meteorology
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 ield-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.
9.1 SWAP
9.1.1 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 low below the groundwater level may include lateral drainage luxes,
provided that these luxes can be prescribed with analytical drainage formulas. The
model is very lexible 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 low
will be impeded when soil temperature descends below zero. To facilitate temporal
detailed studies on surface runoff and diurnal transpiration luxes, evapotranspiration
and rainfall data can be speciied at daily and shorter time intervals. At the model
lower boundary, various forms of head and lux based conditions are used.
In the horizontal plane, SWAP's main focus is the ield scale. At this scale most
transport processes can be described in a deterministic way, as a ield generally can
be represented by one microclimate, one vegetation type, one soil type and one drain-
age condition. Also cultivation sequences and farmer management decisions apply to
the ield scale. Both the physical characterization and the cultivation practices make
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