The rain in spring and early summer fuels plant growth, while the dry conditions later on push the plants to focus more on producing fruit, according to a study published online Monday in the journal Nature Climate Change.
The drought has historically been crucial to achieving the temperatures necessary for the best grapes.
Indeed, there is a solid correlation between early harvests and high-quality wines, with the best wines often being those from when the temperatures are so high the grapes are harvested early.
Since 1981, the average temperatures have been rising to the point that the late-season drought is no longer necessary to achieve the ideal temperature for harvesting.
Over the last few decades, the average harvesting date has crept up an average of about 10 days, according to lead author Benjamin Cook, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory and NASA's Goddard Institute for Space Studies.