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Professor Dr Hans Reiner Schultz is internationally one of the most important researchers on the consequences of climate change in viticulture. In an interview with Alexander Lupersböck, the dean of the Geisenheim University of Applied Sciences (Rheingau) reports on current findings, necessary changes and average temperatures in Geisenheim, which used to be measured in the Adelaide Hills in Australia.Where do you currently see the greatest challenges for the wine world due to the climate crisis?
Schultz: Temperatures are rising globally, more so in the northern hemisphere because the land mass is larger. But there is no patent remedy for all wine-growing regions. You have to look at each one individually because they react very differently. This also has to do with the geographical location on a continent. The development of the water balance alone is extremely different from region to region. The ratio of precipitation to potential evaporation has changed greatly in some regions, but not at all in others. In Geisenheim, Bordeaux and California, for example, evaporation has changed, but precipitation has not. On the east coast of America it is the other way round: there is more summer precipitation while evaporation remains the same. If the air temperature increases by 1 °C, the potential evaporation increases by seven percent; if we were to reach the goal of a warming of 2 °C, evaporation would increase by 14 percent - and this water has to come down again somewhere. This means that the risk of heavy rainfall events increases accordingly.
The wine-growing zones are shifting further north. How far can this go?
Schultz: In the old viticulture books it says: the 50th parallel is the border. It runs right through Geisenheim. We are always talking about the average temperatures from April to October. Wine production needs an average of at least 12 °C. Austria is around 16 °C, in 2018 it was 18 °C. Further north it gets cooler, but I have longer daylight. In 2018, the average temperature during the growing season in Geisenheim was 18 °C. This corresponds to what we measured at the beginning of this century in Santiago de Chile or in the Adelaide Hills in South Australia. Both places are on the 34th parallel. Geisenheim is much further away from the equator and has two hours more daylight - so you can see that the length of the day can compensate for a lot.
What other influences play a role?
Schultz: Mostly the winter temperatures are ignored. Warsaw, for example, is well over 12 °C in the summer months, but in winter it can drop to minus 20 °C and the vines freeze to death. In eastern Germany you can also see that there is more frequent frost. But winters that are too mild mean a higher potential for pests. And: It is important that the vine gets a certain cold stimulus in winter, otherwise budding in spring will be too uneven. The flowering period is also a neuralgic phase. If it is too cool, it endangers the yields. Not every vintage will be as warm as the past three; there can always be a year like 2021. Today we are hardly used to de-acidifying, but 30 or 40 years ago this would have been a good vintage.
What can winegrowers do about rising temperatures and the drought?
Schultz: I say a little exaggeratedly: There is always something you can do in agriculture. Irrigation is often thought of. But this will soon come to an end in many wine-growing regions because vines, as a luxury good, take water away from the necessary agriculture. Irrigation can at most have an intermediate function. In research, we need to pay much more attention to drought-tolerant rootstocks. Today, almost all the rootstocks used still come from breeding against phylloxera. That was over 120 years ago! Today, one has to look at the existing, natural gene pool of the Vitis species with molecular biological tools under completely different aspects. There is much more drought tolerance than in the rootstocks we use today. Since there are only a few institutions addressing the issue, it is an urgent, international task to tackle this research in a collaborative way.
Without piwis, we will not manage to comply with the EU's Green Deal.
Fungal resistance of grape varieties alone is not enough?
Schultz: Without piwis, we will not be able to comply with the EU's Green Deal. Saving 50 percent of plant protection products is a challenge - especially for viticulture, which has the highest consumption of fungicides. We need even stronger resistances there in the future. Breeding and its research is mainly the responsibility of state institutions. In France, this is now being pushed. There is a huge project called Viticulture sans pesticides. Because France is centrally administered, something is happening there. In countries with a federal structure, it is more difficult to organise this. With new tools, we can - and must - move faster. We can no longer assume that we have 25 to 30 years for a breeding generation. By then it will be too late.
Do you expect the grape variety level in Europe to be different?
Schultz: We only know the lower temperature thresholds of the grape varieties, not the upper ones. We have learned the lower ones by "learning by doing". But we assume that Riesling, for example, will no longer function above a certain temperature threshold. But we don't know. Research has never investigated the adaptability of grape varieties to temperatures. Take Chardonnay, for example: it's an adaptable variety. It can be grown in cool but also very warm regions. In the case of Silvaner, I would rather say that it is a sensitive variety. We don't have any reliable data on this yet, it's just empirical values. For example, with the 2018 vintage, which was 4 °C warmer than average, we were able to see what works. The management of pH values in the grape will become even more important. One thing is clear: the character of a grape variety changes over the decades. We can already see from the example of Grüner Veltliner that the peppery character will tend to be achieved in cooler years in the future. But we have possibilities to intervene. Shading with foliage works the easiest. Another effective method, but not so easy to implement, is to change the orientation of the vine rows. But you can't do that everywhere; it's not possible on steep slopes. There is another aspect to this: in Germany, land was consolidated in the 1970s for economic reasons. This increased the slopes. During heavy rains, the water now rushes through the vineyards and leads to severe erosion. The old small-scale structures kept the water in the soil better. But to restore that today is hardly feasible. Nevertheless, regionally specific approaches must be found. We need a successive restructuring of regions so that rainwater does not end up as a highway in the next river and lead to flooding.
We need to change the cultivation systems here so that the existing grape varieties will still work in 100 years.
Where would you plant a vineyard today to make it future-proof?
Schultz: We have to change the cultivation systems here so that the existing grape varieties will still work in 100 years, instead of saying: I'll be in Norway in 100 years. It's not just about the grapes, it's about culture, tourism, tradition. There is much more to wine. And it doesn't just concern viticulture. Soil temperatures rise faster than air temperatures. How can we keep carbon in the soil or put more in? This is a huge challenge for agriculture as a whole. We need to change the way we think. We have to pull out all the stops to keep something long-lasting and sustainable where it has worked long-lasting and sustainable for 2,000 years.
Can permanent cover crop and organic farming help to better maintain the balance?
Schultz: Clearly yes. We have been running an experimental vineyard in Geisenheim since 2006. Plots are cultivated conventionally, organically and biodynamically. This is the longest ongoing trial worldwide. We know from all the data collected worldwide that organic or biodynamic cultivation yields on average 20 to 25 percent less. However, it was noticeable in the warm years of 2018, 2019 and 2020 that the yield of the organic areas was higher than in the conventional ones. This could be an indication that organic systems build resilience more quickly. There are also indicators that organic areas produce less greenhouse gases than conventional ones. If you bring that into the equation, the result is clear. But again, I have to say: the organic system of the present is not the organic system of the future. It has to be further developed and adapted. There are an infinite number of small adjusting screws that need to be researched.
How well are Europe's winegrowers prepared for this path?
Schultz: Viticulture is one of the most climate-sensitive and long-lived crops of all. Winegrowers have to react today to what awaits them in 25 and 50 years. We have been preparing young winegrowers for this for a long time in their training and apprenticeships. They don't have to change everything overnight. But we want to give them the possibilities to react flexibly to changes. There are no standard recipes. You have to observe - and draw the right conclusions.
Photos: © Geisenheim University of Applied Sciences