Drought in the Vineyard
From afternoons at the lake to clinking ice cubes in a glass, sizzling summer days mean everyone looks for a little water to cool off, including grape vines. But this summer California declared water rationing, resulting in restrictions for residents and agricultural businesses alike. And when drought conditions hit wine country, viticulturalists must adapt their practices to help their vines make it through the growing season.
How Do Grapevines Use Water?
Just like humans, grapevines use water to transport nutrients and regulate temperature. Essential minerals dissolve in ground water, making them available for the roots to absorb and move them through the vine’s vascular system.
The vine also uses water to regulate its temperature in a process called transpiration, or the evaporation of water through the leaves, which facilitates the exchange of oxygen and CO2.
Without water, these processes stop, and the vine eventually dies.
Vineyards Designed for Drought
Combating the effects of drought start at the vineyard’s inception. Vineyard planning and design can include adjusting row orientation and planting density, both choices can reduce water requirements.
Most drought-prone growing regions install drip irrigation to better regulate water application, but not all vineyards depend on irrigation. Some use a technique called dry farming. Dry farming means that the vines grow using only the water from annual rainfall.
Many old vineyards planted 50+ years ago are dry farmed. Regional climate, vineyard location, soil structure, rootstock, and planting density determine whether a vineyard can be dry farmed. These vines have deep root systems that make them more drought tolerant.
As for the plants themselves, vines have different water requirements, and vineyard managers select rootstocks with robust drought resistance for areas prone to water restrictions. Even choices around cultivar, or the grape variety that gets planted, plays a role in water use. Some varieties are more drought resistant and heat loving than others. Grenache, for example, thrives in a long, hot growing season.
What Happens to Vineyards During a Drought?
During a drought, vineyard managers monitor evapotranspiration, or the amount of water that evaporates from the vine and ground area around the plant. Viticulturalists can measure how much water a vineyard block loses during a given time period, say one week, and then determine how much water needs to be replaced through irrigation.
Drought conditions can mean winegrowers are unlikely to be able replace 100% of the water loss. Instead, they make calculated decisions for their vineyard irrigation schedule and how much water to use in a process called regulated deficit irrigation (RDI). Depending on where the vine is in its growing cycle, it can handle more or less water stress. This affects wine quality.
For example, when red varieties are just ripening and turning from green to purple in a process called veraison, a little water stress can be beneficial. Limiting water at this stage reduces the number of cells in the berry, resulting in smaller berries. Smaller berries means a lower yield (total crop), but the skin-to-juice ratio will increase, potentially improving the flavor and aroma intensity in the final wine because flavor and aroma compounds are found in grape skins.
Growing Grapes During a Drought.
Growing grapes is something like running a gauntlet: fungal diseases, pests, viruses, erosion - all are part of a series of challenges viticulturalists face each year. Drought is nothing new to those living in California’s wine country, and winegrowers are fortunate to have a range of tools and robust research available to help them get through another challenging growing season.