Climate change continues to increase the likelihood of extreme weather events, including heatwaves. It’s important to plan for these events in the vineyard, including during new vineyard establishment, to minimise the potential negative impact on winegrape quality, yield and the cost of vineyard operations.
‘A heatwave is when the maximum and minimum temperatures are unusually hot over three days. This is compared to the local climate and past weather.” Australian Bureau of Meteorology
What’s considered a heatwave in a cooler climate like the Yarra Valley, may be a typical summer’s day in the warm inland Riverland region; vines acclimatise accordingly.
How will extreme heat impact your business?
The degree and cost of potential damage to your crop will depend on when in the season the heatwave occurs. Depending on the stage of fruit development, excessive heat can cause loss of yield and/or result in fruit downgrades. A heatwave at flowering may reduce yield by disrupting pollination and fruitset.
Where do I find more information and resources on climate and weather?
How grapes get hot & why it matters
Sunburn
“40 - 43°C at the berry surface for just five minutes can cause sunburn of Chardonnay berries at full maturity”
The impact of sunburn on grape quality will depend on the degree of browning and any secondary bunch rot infections that take advantage of grape skin damage.
Learn moreWhat affects grape temperatures?
A range of factors will affect how hot the vines and grapes in your vineyard will get during a heatwave, some of which can be managed to a certain degree. Factors include:
- Air temperature
- The absorption of radiated heat by the grapes (which can be from direct sunlight or sun reflected from nearby surfaces, such as the soil)
- Heat loss through water evaporation or transpiration (evapotranspiration)
What is transpiration?
Transpiration is a plant’s self-cooling mechanism, where small pores on the surface of leaves (‘stomata’) open to allow water to evaporate. Approximately 80-90% of water loss in plants occurs this way. Water needs energy (in the form of heat) to evaporate, so any evaporation will cool the leaves and surrounding area.
What factors affect bunch temperature?
- Water available to the vine
- The strength of the sun and any radiation reflected from surrounding surfaces e.g. bare soil
- Wind speed
- Shade
- Berry/bunch size and how compact it is
- Berry colour – dark berries are affected more than white berries (getting up to 15°C warmer than ambient temperature)
Two key strategies to consider for protecting grapevines from extreme heat
Maximise cooling | Minimise radiative heat |
Irrigate vines to maximise transpiration from the leaves. Use vineyard sprinklers or misters to increase evaporation from vines and vineyard surfaces. | Plant cover crops between rows and under vines to reduce heat reflected from bare soil. Manage vine canopies to keep at least one leaf layer between grapes and sun. Consider artificial shading for high value crops. Apply sunscreen spray (check with winery first). |
The picture shows how a vineyard can be cooled with appropriate irrigation. Rows T4 (yellow) received less than 1ML/ha irrigation and are approximately 8°C hotter than row T0 (blue) which received about 6ML/ha.
Designing vineyards for heatwaves
Designing a new vineyard (or redeveloping an existing one) presents a great opportunity to consider how you can set it up to make the management of your vines during a heatwave easier and more cost-effective.
Choice | What we know |
Row orientation | Row orientation will impact the angle at which sunlight hits the berry surface as well as the availability of potentially cooling breezes. In warm to hot and sunny climates where VSP and other trellis systems with vertical canopy faces are used, a row orientation of east-west or northwest-southeast should be considered. |
Irrigation design | The system must deliver sufficient water to the entire vineyard in the event of a heat event. Use a licensed irrigation engineer/designer when planning the installation of any new irrigation system to ensure it has sufficient capacity and delivery rate. |
Grape variety | Some varieties cope better with extreme heat than others (e.g. Grenache, Mourvèdre, Carignan, Tempranillo, Nero d’Avola, Fiano). Traditional varieties, such as Pinot Noir and Riesling, struggle to maintain flavour and balance under high temperatures. The varieties most prone to sunburn are Chardonnay, Semillon, Cabernet Sauvignon and Merlot. |
Rootstock variety | Different rootstock varieties have varying tolerances to drought. Talk to your nursery for advice. |
Sources:
What irrigation tech solutions are growers using?
Growers are using some great new technologies that have been tried and tested on farm as part of Wine Australia’s agtech adoption program to increase water use efficiency and manage grape yield and quality. Explore the grower experiences below:
Tried and tested water management tools
Wine Australia’s agtech program has worked with tech developers and growers to test water saving and scheduling technology across multiple vineyards. Here is a summary of tools that have been tested for you to consider.
Managing heat in established vineyards
As heat events become more likely, consider what you can do ahead of time during the growing season to prepare your vines for maximum protection and recovery when excessive heat strikes.
Action guidelines for vineyard managers
Before | During | After |
Irrigate | Irrigate to maintain the soil moisture levels needed to prevent wilting and support cooling evapotranspiration. | Irrigate |
Cease deficit irrigation | Monitor for pests and diseases | |
Reconsider any scheduled leaf removal or canopy manipulation |
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Further explanation of the guidelines above
Early season management
Irrigation
Irrigate to support healthy canopy development capable of protecting bunches from the sun later in the season. Test your irrigation infrastructure capacity and consider improvements. Be mindful of water availability and budgets to ensure you have a sufficient amount remaining for a heatwave event ― consider conserving soil moisture by mulching or mowing/spraying midrow swards.
Canopy
Consider sun protection when managing canopies for fruit quality, quantity and disease management ― only one leaf layer is required to protect fruit from sun exposure.
Consider adding foliage wires for additional support if fruit is being exposed to the sun by canopy rolling (more common in young or cane pruned vines).
In hot, sunny climates VSP trellising is not recommended. If already installed, consider retrofitting additions to increase bunch shading (see diagrams under trellis type in this fact sheet).
Mid-row and vineyard floor
Bare dirt will reflect more sunlight onto vines and bunches than soil covered with vegetation. Vineyards with stubble or mown swards and mulch under vines suffer less heat damage. If short on water, consider tossing mown swards under vines to provide mulch.
Click for a range of cover crop topics, including ‘How cover crops affect ground temperatures’ and ‘Cover crops and water use’.
Immediately BEFORE a heatwave
Irrigation
Refill the rootzone soil profile as much as possible.
A 2018 trial of in-canopy misting (ICM), under-vine sprinklers (UVS) and drip irrigation (SI) during a warm night before a predicted heat wave lowered canopy temperatures by 5 - 12ºC, depending on the combination of treatments and site (warm inland vs cooler). Explore your options in this trial summary.
Sunscreens
Spraying sunscreen compounds onto the canopy has been shown to reduce leaf temperature (without any effect on yield) whilst also increasing juice sugar and acids. The sunscreens aim to reduce direct and reflected radiation, whilst also reducing transpirational water loss during the heat of the day.
Sunscreens should be applied before the heat event and only when a heat event is expected. Always check with your winery before applying sunscreens to determine which product is allowed and ensure stock is on hand between flowering and harvest. Only apply at temperatures of 28ºC or less.
When a sunscreen is applied before a heat event:
- Grapes may maintain quality (rather than being downgraded)
- Ripening may be earlier
- Winery processing of the grapes may be easier
Read the findings from a demonstration trial of sunscreen products on Semillon in the Hunter Valley
Canopy
Reconsider any scheduled thinning or leaf removal.
In hot, sunny climates, leaf removal should be avoided or only leaves from the eastern side of N-S rows removed.
Immediately AFTER a heatwave
When monitoring for damage, remember that heat damage may take a few days to be visible.
Irrigation
Irrigate to top up soil moisture levels and reduce vineyard temperatures.
Pest and disease monitoring
Sun damage to grape skin can leave it open to attack by secondary infections (e.g. botrytis and other rots). Stay vigilant and be prepared to take action, especially if the heat event is followed by rain.
If resources (e.g. labour, water, irrigation system capacity) are limited, prioritise blocks for reducing heat damage by considering the following factors:
- Crop value
- Stage of vine development (which will affect the impact of the heat)
- Soil depth and texture
- Block aspect
- Age and type of grape scion and rootstock
Australia's Wine Future: A Climate Atlas
A free online resource of climate information for all Australian Geographic Indications (GIs), containing climate projections and detailed information about how the climate may change in the near, mid and long-term horizons.
Read more and download