The Bordeaux climate could be classified as oceanic-temperate, with moderate temperatures in both winter and summer. There are on average 2,000 hours of sunshine per annum. The nearby Atlantic Ocean has a major effect on the difference between day and night temperatures. Cool nights in the summer help to keep acidity levels in the grapes high, also helping ensure that they stay healthy. Cool night-time temperatures also have an important effect on the aromas and flavours produced in the grapes.
The Weather
As the weather warms up in March or April the buds on the vines start to burst. At this time of the year frosts can be a problem. In 1991, a large part of the crop was lost due to temperatures as low as -7 degrees Celsius in mid-April.
Annual rainfall is about 700-800 mm. Summers are often sunny and dry, the weather is normally very pleasant, although temperatures have been known to reach 40 degrees Celsius!
Excessive or untimely rain and other problems like hail (especially in spring and summer) cause more harm as the growing season progresses. Rain during the later stages of the growth cycle is not desirable because the roots carry water directly to the grapes, thus diluting the final wine. However, this depends on the type of soil. Gravely soil allows rainwater to drain away very quickly, whereas clay-based soil retains water. At this stage, moist soil can encourage nearly ripe grapes to rot.
A particular problem is hailstorms, which can wipe out the whole crop in minutes. The hailstones can easily be as big as eggs - damaging more than just the vines. Hailstorms are very localized, so generalizations should not be made about their effects throughout a given region or vintage.
The ideal weather for harvesting is dry and slightly windy. The wind helps evaporate the morning dew and the grapes can be gathered in perfect condition. Moisture and rain not only cause grapes to become diluted, but water can also cause grey rot. Great wine can only be made from first class grapes and so quality-conscious viticulturists try to do everything they can to avoid rot and produce top quality grapes. Hand picking will allow us to only process the healthy grapes. Rain, however, causes many other complications to the vintage routines, too.
It must be said as well that global climatic change seems generally to make the weather conditions and waterfall more variable from one year to another.
