Geoscience Reference
In-Depth Information
Vineyard microclimate
APPLICATIONS
There are two popular beliefs about wine cultivation. First, that the vine thrives in a harsh environment and, second,
that the best-quality wines are produced in regions of marginal cultivation. The importance of soil characteristics is
often stressed, with drainage and physical composition of the soil being most significant, but climate and weather
conditions undoubtedly play a major part. Vines will grow only within certain climatic limits, with cool, moist climates
like that of southern Britain forming the northern boundary and the semi-arid climates of a Mediterranean-style climate,
such as California or South Australia, forming the tropical limits. Superimposed on this broad climatic zone,
viticulturalists find that microclimate can play a role in determining the quality of the grapes. Grapes need adequate
warmth, protection from spring frosts, abundant sunshine in summer, and shelter from wind at critical times in the
growing season.
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 equator-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 of Germany, many of the south-facing slopes are covered with vineyards
to take advantage of this greater thermal input (
Plate 8.3
).
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 wind 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, quality and value of the grapes.
trees without accumulating. A classic example of a frost
hollow has been found in the Austrian Alps. A lime-
stone sinkhole with a steep back wall facing north-east
allowed cold air to become stagnant.
Figure 8.13
shows
temperatures at different levels on one particular night.
Towards west-south-west the sinkhole is intersected by a
col which allows the stagnant cold air to remain in the
lowest 50 m of the basin. Temperatures as low as -51
C
have been recorded when the ground was snow-covered.
Even coastal Antarctica is usually much warmer than that!
The frequent occurrence of frost has affected vegetation,
so that few trees grow near the base, to give an inverted
vegetation gradient.
the Mosel valley, Germany.
Photo: Peter Smithson
