Differentiation of local climate in the Alsatian vineyard

Abstract

Climatic and soil characteristics are the main factors affecting the qualitive potential of a vineyard. At the scale of a « terroir », it is important to know the variability of the local climate (mesoclimate). Therefore, we studied landscape parameters (altitude, slope, etc.) affecting the local c1imate of vineyards in Alsace (NE FRANCE), at six sites each representative of a« terroir» type during 1991,1992 and 1993. Climatic variables were measured hourly and daily throughout the growing season (April - September).

Wind speed was the climatic variable which was most affected by the landscape. The angle of opening of the landscape, its altitude and its orientation are the main factors differentiating the terroirs which were compared.

The variabiliy of global solar radiation depends on the slope, the orientation and the height of and distance to topographics elements. This variability depends on solar angle and is smallest in June.

We observed small differences for average seasonal temperature between sites. On the other hand, more detailed studies considering different daily weather conditions (cloudy versus clear weather) and measures per hour and day contributed to a better differentiation between sites. In cloudy weather conditions, temperatures depended on altitude only (thermic gradient -O,6°C/100 m). In clear weather conditions, night temperatures depended on the altitude and the slope of the site; day temperatures were also influenced by the orientation, and the angle of opening of the landscape and the characteristics of the soil surface.