Environmental Engineering Reference
In-Depth Information
Using suitable techniques it is possible to choose sites which have the best
microclimates and so give better wines. In areas which are near the margin of climatic
suitability because of low temperatures, steep south-facing slopes can be used that will
receive a greater input of solar radiation at the micro-scale and so enhance the sugar-
producing quality. In the Mosel valley and the Rheingau many of the south-facing slopes
are covered with vineyards to take advantage of this greater thermal input (Plate 1). As
frost can cause damage to blossom in spring or affect the mature grapes in autumn, sites
need to be chosen that minimize frost incidence. Frost in these seasons is most likely to
be caused by radiation losses during clear skies with dry air. Cold air can drain
downslope, giving the lowest temperatures in the valley bottom sites. For the vines a
safer location is at some distance above the valley floor. It has proved possible to increase
warmth by retaining stones within the rows of vines. They absorb sunlight during the day
and release this heat in the evening, rather like storage heaters. Shelter from wind is also
important, so that sites protected from the prevailing or dominant winds are most
advantageous. In Portugal, where winds can be a problem, vines are grown in forest
clearings in the Dão region, and on the exposed Atlantic coast at Colares, near Lisbon,
they are protected by plaited cane fences.
By using natural features or providing artificial ones the microclimates in vine-
growing areas can be made more favourable to improve the yield and quality of the
grapes.
Figure 8.13
Night-time energy exchanges. The magnitude of
the components will vary greatly, depending upon weather
conditions such as cloud amounts, wind speed and humidity.
Of much greater importance at night is what happens to the air as it cools through contact
with the ground surface. As the air becomes cooler it gets denser. If the surface is flat the
cold air remains at ground level to give the normal temperature inversion. However, on a
slope the cool air may move downslope as a katabatic wind or density current, increasing
in strength and volume until it meets a physical barrier, such as a wall or embankment, or
until it is no longer colder than its surroundings. Once the cold air stops moving it
