WinePedia - The Wine Encyclopedia

Site and Topography

The site of a vineyard mediates between the predominant soil and the overall climate of the region. By dint of a particular aspect, the climate may have, say, a more south-facing aspect than is general, or the soil may be modified by erosion. The winding Mosel valley offers many sites; the best are those with a southerly aspect on a hillside. The flatter parts of the region make less fine, less intense wine.

Other factors can also be decisive. Isolated hills encourage airflow, thus reducing the chance of frosts in late spring. Rivers also reduce the likelihood of frosts because they tend to raise the prevailing temperature slightly through airflow. Altitude can also be decisive; a rise of 330 feet (100 in) reduces the average temperature by 2'F (0.6'C). Site can be modified by human intervention. Trees are often planted to act as windbreaks. Eroded soil can be taken from the foot of a slope back up to the top.

THE RHEINGAU-A CLASSIC
EXAMPLE OF THE IMPORTANCE OF SITE
Although it is quite a large region, the Rheingau in Germany is a good example of how site can modify the overall climate and situation of a wine region. In this case, it turns an area in what is a very marginal latitude into one of the country's prime wine regions. The site modifies the position in a number of ways:

1.) The river Rhine, which generally flows south north through Germany, turns east-west at this point. This gives some riverside slopes a southerly aspect, maximizing sun exposure at the warmest part of the day.
2.) The Taunus Mountains to the north protect the vineyards from the cold winds that blow down from the Arctic.
3.) The river provides airflow, reducing air pockets, thus limiting the development of frosts.
4.) The river provides some reflected light onto the slopes, which is crucial to aid the final ripening in a cool northern fall.
5.) The river encourages mists in some years, which are necessary for the development of "noble rot" to make great botrytized sweet wines.