Integrated Applications - Transport in the Atmosphere-Vegetation-Soil Continuum - page 300

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(b)

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Figure 8.8 Temporal development of latent heat lux (a) and sensible heat lux (b)
during a 30-day dry-down. Comparison of climatological conditions (clim.) and heat
wave conditions (HW) for grass and forest. Unstressed luxes are identical to those
given in Table 8.6 . Grass and forest differ not only in unstressed lux, but also in
rooting depth.

the irst signs of reduction of evapotranspiration is due only to the shallower rooting
depth of the grass. From day 12 onward the evapotranspiration starts to fall and stays
below the value of the forest. The evapotranspiration decreases approximately log-
arithmically in time (see Teuling et al., 2006 ). Through the constraint of the energy
balance, a decrease in the evapotranspiration leads to an increase in sensible heat lux
( Figure 8.8b ). Because the initial sensible heat lux of the grass was below that of the
forest, it takes some additional days before the sensible heat lux of the grass exceeds
that of the forest (approximately 2 weeks after the start of the dry down).