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Our Vineyards Face a Changing Climate

Voices

John van der Linden01 February 2020

BB51

Hawke’s Bay is New Zealand’s second largest wine region after Marlborough, providing substantial income and employment within the vineyards, wineries and service industries and for the associated tourism, food, accommodation and travel sectors. 

Hawke’s Bay’s diverse range of geography, soils, meso-climates, skilled viticulturists and winemakers mean that the region produces fantastic wines from a wide range of varieties, and this is confirmed by the number of national and international awards the region regularly wins. 

The range of Hawke’s Bay special vineyard sites include the world-renowned Gimblett Gravels appellation with its unique combination of warm summer temperatures, low summer rainfall and stony, alluvial, low-fertility, free-draining soils which grow the classic red grape varieties such as Cabernet Sauvignon, Merlot, Cabernet Franc, Malbec and Syrah. 

Hawke’s Bay also has many great inland vineyard sites that have a high diurnal temperature fluctuation, which is very important for producing white wines such as Chardonnay, Albariño, Pinot Gris and Sauvignon Blanc. The warm daytime temperatures and the cooler night-time temperatures of these inland sites allow the white varieties to ripen slowly, while developing flavour, aroma and sugar in natural balance with the acid to give them freshness with fruit richness. 

Wine strongly expresses ‘Terroir’, or specifically the climate, soil and how the people grow grapes and make the wine. While climate and soil play a huge part in wine quality, it is also the people who decide what vines to grow where and how they are managed. With the changing climate and increased extreme weather events, it will also be the people who decide how to adapt their vineyards to these changes.

Hawke’s Bay produces a diverse range of wonderfully naturally balanced wines. If the climate changes and the growing seasons become too warm, then the resulting wines get out of natural balance with overripe flavours, high pH, low acid and high sugar (high alcohol). If the grapes are picked early in these conditions to get lower alcohol and higher acid, then the flavours, aromas and phenolics (tannin) will not be ripe. So what can we do? 

Adapting vineyards 

There are two main challenges to adapt our vineyards to changing climates. Firstly, making the current vineyards more resilient to the climate extremes and managing the vines to produce consistent wine styles. Secondly, exploring new sites, new varieties and new techniques to respond to the changing climate.

Here are the weather challenges to which our vineyards must adapt. 

Warmer winter temperatures. While there a fewer frosts, warmer winter temperatures will result in less winter chilling for the vines resulting in poor and uneven budbreak. This could lower yields, increase ripeness variability and reduce wine quality. Warmer winter temperatures can also increase pest pressure from reduced winter pest mortality and can increase the threat of new pests and diseases establishing in New Zealand.

Higher summer temperatures and higher light intensity. Higher summer temperatures can result in vine stress, sunburn of the fruit and a change in the flavour and structure of the wine. The grapes can ripen too quickly with the wine being out of natural balance, with high sugar resulting in high alcohol, lower flavour and low acid resulting in flabby, white wines without freshness and structure. 

This can be partially addressed by leaving more leaf cover over the fruit, however it is a fine balance, as too much shade can also change the flavour profile of the grapes and contribute to increased disease which also can affect quality and yield. Adopting slower ripening techniques, such as trimming to make smaller grape canopies can also slow sugar accumulation to achieve this natural balance.

The best long-term strategy in a warming climate is to find cooler, higher altitude inland sites to allow the grapes to ripen more slowly. Planting later ripening varieties in these warmer sites is another way that natural balance can be achieved.

More drought. While vineyards use less water than many other crops and some older vineyards on deeper soils are dry-farmed, younger vineyards on very stony sites still require irrigation.

Most water in Hawke’s Bay comes from artesian bores, however during droughts some of these bores must be shut off, resulting in water stressed vines and poor yields of poor-quality fruit. In the case of severe water stress, the vines will defoliate resulting in the compete loss of crop.

Storing water in dams is the way that many parts of the world adapt to drought, however productive land is required in a dam, and they are expensive.

The vine’s water requirement can be partially reduced by ‘conditioning’ them in spring by applying less frequent irrigations resulting in smaller diameter xylem vessels that will help it cope with water stress later in the season. The use of seaweed sprays also helps the vine cope with some degree of water stress. 

Another key vine conditioning technique involves burying an irrigation dripline 30 cm below the soil surface. Water is applied directly to the deeper vine roots only when required and this results in less water loss due to evaporation, less weed competition and encourages a larger, deeper root system that in-turn becomes less reliant on regular irrigation. The other key benefit of a deeper root system is that they will not absorb water from heavy rainfall events as the grapes ripen, thus avoiding dilution, splitting and rots later in the season.

Water scheduling for some vineyards is now carried out using a scientific instrument called a ‘pressure chamber’ to directly measure the vine water stress, rather than methods in the past that only measured the soil moisture content. This means that the vines are watered only when required and this improves quality and helps builds vine resilience … and obviously conserves water.

Drought can lead to more fires and smoke taint in wines from forest fires is an issue that Australia regularly faces. New Zealand has also had fires near vineyards recently and so smoke taint is a real threat that could result in complete crop loss.

One positive of drier summers is less disease pressure for some diseases such as botrytis, downy mildew and Phomopsis, however the incidence and severity of other diseases such as powdery mildew may increase.

Protecting the soil. A healthy soil is essential to make quality wine, so viticulturists protect and build healthy soils by adding organic matter to help it hold nutrients, water, sequester carbon and to encourage microbial activity for nutrient cycling. This practice will partially help buffer against drought.

New sites, varieties and techniques. As the climate changes, viticulturists need to explore new sites, new grape varieties, including new clones and rootstocks, and continually evolve vine management techniques. As temperatures increase, more white varieties will be planted in cooler, inland, higher-altitude sites to retain acid freshness, flavour, aroma and natural wine balance. 

Outstanding Chardonnay, Pinot Gris and Sauvignon Blanc vineyards are now grown in the inland, elevated Crownthorpe and Maraekakaho valleys, as well as pockets of central Hawke’s Bay. Chenin Blanc and the Spanish white variety Albariño are recent additions to these plantings, with experimental plantings of other varieties too. On the hotter plains, viticulturists are experimenting with later ripening varieties like Grenach, Tempranillo, Petite Verdot, Durif, Tannat and some Italian varieties such as Barbera. 

While the changing climate can be viewed as a threat, it is also an opportunity to continually improve the wines. Given the fantastic natural resources of Hawke’s Bay, our skilled viticulturists and winemakers will adapt to these climate challenges to continue to bring you your favourite wine to enjoy for many decades to come. And who knows, in a few years you might even discover a new favourite variety from a new site!

John grew up in the Esk Valley and has been involved with growing grapes since age 9. He developed and managed his own vineyards and lectured at EIT for 10 years in horticulture and viticulture. He has been a viticulturist for Church Road Winery, Crossroads, Yealands Estate and the Villa Maria family of wines. 

John van der Linden01 February 2020

BB51

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