One of the many factors of weather or in the long-term course of the climate. Strong air movements can have both positive and negative effects on the vineyards. Hot, dry winds such as those in Australia or the Scirocco, which blows from the Sahara towards the Mediterranean and reaches southern European wine-growing areas, can be dangerous. Equally feared are cold winds in valleys, such as the notorious Mistral on the southern Rhone. At high stress levels, vines can also be subject to wind stress, resulting in lower yields, impaired growth of shoots, foliage and grapes. The vines close the stomata in the leaves to protect them from the wind, which results in reduced photosynthesis and later ripening of the grapes.
Due to lower wind force the humidity between the vines is also better preserved, which can be especially important in dry areas. Harmful effects are prevented by plant covers (protective trousers) made of plastic or wind breakers (barriers made of vegetation or artificial facilities). So-called wind machines (blowers) stir up the cold soil air and mix it with warmer layers above. This combats the dreaded radiation frost (frosty nights with no wind), which is common in California's Napa Valley, for example. Damp sea winds can have a positive moderating effect in dry or low-precipitation wine-growing regions such as areas of Portugal, California and South Australia. See also under frost, drought, thunderstorms, hail and climate.