Climate and Wine Quality: Rainfall

The general implications of rain for viticulture are discussed under rainfall.

Opinions differ as to optimum rainfall amounts during ripening. Most agree that any severe water stress at that stage is deleterious. On the other hand, heavy rain can lead to temporary juice dilution and sometimes to incomplete ripening, especially if accompanied by lack of sunshine. Wet ripening periods commonly signal poor vintages. Heavy rain close to maturity is especially damaging, because it can cause berry splitting and subsequent fungal infection of the bunches (see botrytis bunch rot). This occurs most typically in certain varieties with tight bunches, such as Chenin Blanc and Zinfandel, and where the vines were under drought stress prior to the rain. hail at this time can be devastating.