Climate change and its interaction with winegrowing

A Radio NZ article about University of Waikato student Electra Kalaugher and her work on climate change and dairy farms, and the accompanying video was particularly timely, because at about the same time I was answering a questionnaire sent to me by a student studying an MBA in Bordeaux. Her thesis is on climate change on winemaking and how it concerns the French legislation relating to the wine industry.

Below are her questions and my answers to them. My thanks to her for permission to post the information here...

1-Climate change has been affecting the wine industry, like all fields in agriculture. What is your experience in the vineyards of New Zealand so far?

Of those events that are supposed to be altered with climate change, in recent years I think we have seen wider swings in weather events, such as rainfall, snow, frosts and the like. We have had some periods of significant drought, as well as highly unusual heavy rainfall. We have seen some late season frosts, and unusually large amounts of snow in some areas. However, it remains to be seen whether these events are considered to be abnormal in the longer term.

2-Do you think New Zealand will benefit from the climate change since the warmer areas expand?

It is possible that new geographic areas will open up to winegrowing as a result of the overall warmer temperatures. However, this will have implications for the existing areas, where the warmer climate may mean that making wine styles associated with a particular region could be made more difficult. For example, the Marlborough style of Sauvignon blanc is associated with the cooler ripening period that the region has experience. If temperatures rise, the flavours in the wines will also change, and so the wine style.

This is one challenge, and another significant one is the chance of more extreme weather events. Of the possibilities, early season or late season frosts are a particular concern for the wine industry, as many areas are already prone to damaging frost events, so having them occur later into the growing season, and earlier as the season ends and harvest approaches, will have a direct impact on profitability.

Some forecasts for seasonal changes in precipitation point to less overall rainfall as a result of climate change in the eastern parts of New Zealand. Therefore, water will become an even more valuable resource, potentially limiting grape production.

Overall, I do not think that climate change will be a beneficial thing for the New Zealand wine industry, but the reality is that we will have to deal with it.

3-What are the challenges that the wine producers have been facing due to climate change effects?

I've mentioned some of these already - the possibility of frosts happening later in the beginning of the season and also happening before fruit is harvested. Water availability has been an issue with the establishment of newer vineyards, with water schemes needing to be developed to ensure a reasonably reliable water supply. Increased heat means that some grapevines will need to be grown slightly differently in order to retain the flavour profiles that are wanted in the wine. Severe flooding has had minor impacts on vines so far, but this will probably be more of an issue in the future.

4-What kind of changes should be made in the vineyards in order to adapt the shift in climate?

Viticulturally, it will be necessary to change the management of the vines to retain flavour profiles - for example, doing less leaf removal, or changing its timing. Trellising systems may need to be changed to help with this, as Vertical Shoot Positioning, which is the most widely used system in New Zealand, may give the fruit too much exposure.

Irrigation management (and linked with that, cover crop management) will have to be tweaked to ensure vines don't get water stressed at inappropriate times. More efficient ways of delivering water to the vines, and measuring soil and grapevine water status, need to be developed.

With frost events potentially happening when vines have more canopy on them, more efficient ways of dealing with frosts will be needed. If enough water can be found (which is unlikely for large vineyards), sprinkler systems will work, but most are using fans or helicopters at the moment, which rely on the presence of an inversion layer, which holds warm air. As well, it isn't certain how climate change will alter the occurrence and strength of inversion layers...

New vineyards should be planted with future shifts in climate in mind. This encompasses most aspects of vineyards, but also variety choice and potential wine styles to be produced.

5-As a viticulturist, what are your conclusions for the future concerning the climate change effects, for New Zealand and also globally?

In my mind at least, climate change is a reality that we should be ready for. Planning for its occurrence, using the latest forecasts (e.g. NIWA's Climate Change Scenarios for New Zealand), is the best we can do. 

The wine industry will be able to cope with climate change, but it will likely have an impact on the financial planning, with increased risk of crop loss and increased management costs. The possible changes to wine style also need to be considered carefully, as the consumer may want to stick with the current style, but it may not be able to be grown in the same area or it wouldn't be cost effective to do so given the extra labour inputs.

Frosts in California (and elsewhere!)

I have mentioned frosts before (August 14 and October 17, 2009), but some recent news brings this subject up again.

Early season frost is a big problem in New Zealand, but also in a lot of other growing regions around the world, such as in Ontario, which I've talked about before. The latest news from California, in an article from Western Farm Press, details the aftermath of a couple of frost events on April 8-10 in areas south of San Francisco. Damage estimates suggested that about one-quarter of the 10,500 hectares of grapes in the Paso Robles area will have a crop that won't be commercially worth harvesting.

Any grower worth his weight in quality secateurs should know what the frost risk is when looking to develop a vineyard, and if the risk is perceived as being great enough, some sort of management system will be planned for the development

Results of a severe spring frost - all green tissues of the vine are completely decimated

If the frosts are mild, then passive means, such as having bare soil between the rows in the spring, which will maximise heat accumulation during the day and release at night, can give from 0.5 to 1.0°C protection (of course, careful decision making in site selection is the best means of passive management!).

Active means of management include such things as taking advantage of an inversion layer (where a layer of warm air sits above the cold air at vine level, and which tend to form on still nights with clear skies) and sending up a helicopter to push the warm air down to mix with the cold.

However, if the frosts are very frequent, then installing a permanent system becomes cost effective, such as the wind machines I've already written about, or using water sprinkled over the vines.

A frost fan installed in Central Otago. Plenty of snow-capped mountains around the area!

There are some big differences between the wind and water methods. The movement of air method relies on mixing the warmer air in an inversion layer with the cold air on the ground. This works great unless 1) the inversion layer doesn't have enough warm air to raise the temperature of the cold air to above freezing or 2) there is no inversion layer.

The former is heartbreaking, as you might be successfully fighting off the freezing temperatures, then just before dawn and the temperature rise that comes with it, the inversion layer is all used up and the grape buds freeze.

The latter has the same outcome, but then you don't have to spend all night running around trying to combat the frost!!

In some cases, the conditions are not right for an inversion layer to form, or the cold might be coming in as a mass of freezing air, for example, from nearby hills or mountains that have recently been covered by snow (this appears to be what happened in California recently). In this case, since there is no warm air around, fans and helicopters won't help. However, the application of water to the plants will work for all types of frost events.

The idea behind the application of water is that as water goes from liquid to solid form (freezes) it releases heat (heat of fusion).

So as long as water is freezing on the plants, heat is being released, effectively keeping the temperature at 0°C. Plant tissues can survive this temperature and even a bit lower without damage, so as long as enough water is supplied to always have some in the process of crystallising, the ice, and grape buds or shoots inside, will be kept from temperatures that might damage them.

Two types of post-mounted micro-sprinklers - these use quite a bit less water than the traditional impact-type overhead sprinklers

The down side is that if enough water is not applied, the temperature can continue to decrease, so if the application system breaks, or the water runs out, before the air temperature rises sufficiently, you can lose the new growth.

In the foreground row visible in this picture there is a number of vines where less growth is visible. This is because the sprinkler at the top of the post (centre left in the photo) failed during a frost event, meaning that the vines were not continuously covered with water - thus once the freezing stopped, the temperature of the ice and tissues within dropped to damaging levels. Note that there is a frost fan in the background - the fan isn't able to cover the area that these vines are in, so the sprinklers were put in to provide protection there.

My preference, if I were to plant in an area that was prone to frost events, would be to use water sprinklers. However, in some cases there wouldn't be enough water available for this. Large dams can be build to provide a source of water, but sprinkling even a hectare of ground with water for a decent frost can require up to 40 cubic metres of water per hour depending on the system used!

The concerning thing is that with global changes to climate, we should be prepared for more extreme weather events - in this context, we need to be ready for more severe frosts later in the season. Seeing as how some grape growing regions in New Zealand can have a potentially damaging frost in almost every month of the year (historically, anyway), this isn't good news!!!

Hands up those who thought being a viticulturist was a cushy job!!

How low is low enough?

First of all, let me say how lucky I feel for my family and home to have made it through the Christchurch earthquake with so little effect - my best wishes go to those that were not so fortunate!

However, despite the 7.1 magnitude earthquake, the vines continue developing! And about 10 hours after it hit, we were out in the vineyard, finishing up the pruning! This because we're on a pretty warm site for Canterbury, and the buds were showing signs of pushing, making it more difficult to prune. At this stage, the buds start getting more susceptible to being rubbed off, so pulling brush can be a very time-consuming affair if they get too far along!

So once that was finished, I could put on a lime-sulfur spray, which should help control any carryover powdery mildew that could have been left as dormant hyphae on canes left for the coming season.

Powdery mildew infections on dormant canes - the dark blotches are areas where the fungal hyphae have gotten into the shoot tissue during the season

Then came the job of getting ready for spring frosts! This takes the form of mowing the cover crop as closely as possible, so that as much solar energy as possible can be absorbed during the day, and the also released at night. A higher growing cover crop can insulate the soil from gathering the sun's energy during the day, and also keep it from radiating that heat at night, causing an increased frost risk.

So as the grass was relatively high, I had to do a first pass, and then another cut with the mower.

Closeup of the first (upper third) and second pass (lower two-thirds) of the mower. You can see that I've cut the grass shorter than it's been in a while as it's more yellow than the grass in the background.

A longer view of the row (sorry for the "Batman" angle!). First pass on the right, and second on the left.

So we're still a ways away from budbreak (meaning green tissue visible on the buds), and therefore the most sensitive time for the shoots to freezing temperature, but even now they are starting to be more susceptible to frosts. I will be keeping the grass as short as possible over the next few months!!

Frost in the late throes of ripening

Just a quick note about late season frosts, while they're happening in Niagara. In New Zealand, early season frosts are a common problem, but not so much late season ones. I've already written about the use of wind machines in the dormant season (Aug14), but this season Niagara is in the situation of having many grapes (Chardonnay, Riesling, Cabernet franc, Syrah...) still out on the vines, and yet temperatures are dipping to below zero.

One reasonably strong frost event can kill all the green leaves on the vines, which means that the ripening process effectively stops (a small amount of sugar may accumulate in the berries due to the vines dipping into their carbohydrate reserves, which isn't good for long term vine health, sugar concentration may increase due to berry shrivelling, and then there may be small changes to acidity and flavour). Leaving the fruit on the vine won't help when you're trying to make normal table wines (icewines are a special case!), and if the vine tries to push a bit more sugar into the fruit using its reserves, it will be less resistant to cold temperatures during the winter, and may suffer a bit in the early season following.

So the fruit has to come off, ready or not!

To prevent the leaves from making an early departure, the wind machines can be used (providing there is an appropriate inversion layer) to keep the temperature dipping below zero, and keeping the leaves on the vines so they can photosythesise a bit more, hopefully ripening the fruit.

Even though the daytime temperatures are cool at best right not, there can be a significant amount of activity in the vines and fruit if it's sunny. The sun's radiation can heat fruit and the leaves to above the air temperature, so enzymes can be rockin' along quite nicely if it's not overcast or too windy.

Ironically, clear skies and lack of wind are exactly the kind of conditions under which frosts form, so what you want during the day isn't what you want and night!

We're keeping our finger's crossed for still air and sunshine during the day and clouds and a gentle breeze at night!!

Wind Machines

Since I'm here in Ontario for a while, one does get to touring around vineyards (and wineries!) a bit.

In NZ, wind machines are popping up all over the viticultural landscape, as the most common type of frost occurring in the spring are radiation frosts. Something that moves the air can be very effective in avoiding freeze damage to the vines, because in such a frost cold air develops near the ground, but warmer air accumulates on top of that cold air. This is called an inversion layer, with the warm air stacked on top of the cold.

A wind machine sticks up far enough above the ground (say, 10m) to draw this warmer air down and mix it with the colder air. In most cases, there is a significant reservoir of heat in the inversion layer, meaning that the mixed air is warm enough to prevent freezing of the vine tissues for many hours.

Helicopters are also used to mix the cold and warm layers, but if a vineyard is in a location that is hit consistently with frosts, it can be worth the capital cost to buy, install, and maintain the fans.

So in NZ there are a lot of wind machines being put in to help manage spring freeze events, but here in the Niagara region, they are also putting them in. However, spring frosts are not so much of a concern here (due to the general climate and also the location of the vineyards). So why are people investing in these expensive machines?

Here the main problem is freezing temperatures during the dormant season. Grapes can be very hardy plants, surviving very low temperatures (for certain species, this can be down to less than -40 degrees C!), but vinifera vines tend to be more tender, with a critical temperature of around -18C. So if the temperature in a region tends to get lower than this on a regular basis, you had better have some methods to manage the vines to prevent damage!

One method relies on the presence of the inversion layer, which can appear in the middle of winter as well as in the early spring (or autumn). By mixing the air, freezing temperatures low enough to damage dormant vine tissues can be avoided, leading to productive vines the next season. Without some form of protection, crop losses can be 100 percent, with the added burden of having to re-train the vines (if you're lucky) or re-plant them (if you're not lucky!).

I will write on other strategies to avoid winter freeze damage in another post...