The best wine growing regions in the world tend to lie between the 30° and 50° latitude on both sides of the equator. Wine producing areas are divided into two climactic types, maritime and continental. The maritime climate is characterized by proximity to a large body of water, such as an ocean. Compared with a continental climate, it has higher rainfall, higher humidity and less daily/seasonal temperature variation due to the “moderating” impact of the body water. A continental climate tends to be drier and sometimes sunnier, and experiences more daily and seasonal temperature variation.
To produce grapes suitable for wine making the annual mean temperature needs to be at least 50°F. A lower average mean temperature means the winter is probably too severe and the vines will suffer serious damage, or the summer is probably too cool for the grapes to adequately ripen. Vines begin to grow when the temperature is about 50°F (if it is colder they remain dormant) and they flower when the average daily temperature is about 66°F.
An area’s temperature variations from the highs of the day to the cool of the nights (diurnal temperature shift) also impact a wine’s characteristics. Greater temperature variations produce grapes with high acid and high sugar content as the exposure to sunlight increases ripening while the sudden drop in temperature at night preserves the balance of natural acids in the grape. If the nights are warm, you’d end up with ripe but very low acid grapes, resulting in big, “jammy”, alcoholic wine – which is not that appealing to most people.
The amount of water a vine needs depends upon a variety of factors including its age, size, the ability of the soil to retain water, the humidity, etc. Adequate water is particularly important in the spring, when the vines are about to flower and in the early summer when early summer at the onset of ripening.