Come Rain or Shine

Talking Wine, Weather, and Science: Part 2

February 03, 2021 USDA Southwest Climate Hub & DOI Southwest Climate Adaptation Science Center Season 2 Episode 3
Talking Wine, Weather, and Science: Part 2
Come Rain or Shine
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Come Rain or Shine
Talking Wine, Weather, and Science: Part 2
Feb 03, 2021 Season 2 Episode 3
USDA Southwest Climate Hub & DOI Southwest Climate Adaptation Science Center

Is climate change already impacting viticulture (the cultivation of grapevines)? How might a changing climate affect wine production? Is today a better time to drink red wine in Germany? Does weather affect alcohol content? You might be surprised by the answers to some of these! In this second half of our two-episode feature on viticulture, we delve into the effects of climate, weather, and our changing future on viticulture. If you haven’t already, be sure to listen to Part 1 where our guests, Dr. Kerri Steenwerth with USDA-ARS in California,  Dr. Andy Walker, from UC Davis, California, and Dr. Jeremy Weiss, from University of Arizona, introduce themselves and their role in supporting the industry. Image credit: USDA.

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Sustainable Southwest Beef Project (NIFA Grant #2019-69012-29853): 

Show Notes Transcript

Is climate change already impacting viticulture (the cultivation of grapevines)? How might a changing climate affect wine production? Is today a better time to drink red wine in Germany? Does weather affect alcohol content? You might be surprised by the answers to some of these! In this second half of our two-episode feature on viticulture, we delve into the effects of climate, weather, and our changing future on viticulture. If you haven’t already, be sure to listen to Part 1 where our guests, Dr. Kerri Steenwerth with USDA-ARS in California,  Dr. Andy Walker, from UC Davis, California, and Dr. Jeremy Weiss, from University of Arizona, introduce themselves and their role in supporting the industry. Image credit: USDA.

If you’re enjoying this podcast please consider rating us and/or leaving us a review on Apple Podcasts, Podcast Addict, or Podchaser Thanks!

Have comments or episode suggestions for us? We welcome your feedback! Please share your thoughts and suggestions here:
Follow us on Twitter @RainShinePod
Never miss an episode! Sign up to get an email alert whenever a new episode publishes

Affiliate links:
DOI Southwest CASC:
USDA Southwest Climate Hub:
Sustainable Southwest Beef Project (NIFA Grant #2019-69012-29853): 

Emile: [00:00:00] Welcome to Come Rain or Shine, podcast of the Southwest Climate Hub and the Southwest Climate Adaptation Science Center or CASC. I'm Emile Elias, director of the Southwest Climate Hub. 

Sarah: [00:00:12] And I'm Sarah LeRoy, Science Communications Coordinator for the Southwest CASC. Here, we share recent advances in climate science, weather and climate adaptation and innovative practices to support resilient landscapes and communities.

Emile: [00:00:27] We believe sharing this information will strengthen our collective ability to respond to impacts of climate change in one of the hottest and driest regions of the world.

Hi and welcome to part two of our two episode feature on viticulture. In part one, we discussed the basics of viticulture and why we might be interested in it. In this episode, we'll delve into the effects of climate, weather, and our changing future on viticulture. 

So I have a question for all three of you. Do you think growers are already seeing impacts from weather variability and climate change? And we'll go ahead and start with Jeremy first on this question. 

Jeremy: [00:01:17] Yes. Without a doubt. Climate change is impacting viticulture and wine grape growing around the world. And some of the reading that I've been doing over the past couple of years, there's been documentation from Europe, for example, where the growing season is starting two to three weeks earlier, if not a little bit more, perhaps a little bit less, but you know, it's starting earlier because of warming regional temperatures. 

And what's that what that's doing is, well, first, it depends on where you're growing the grapes, whether it's a relatively warm region or relatively cool region. But what that's doing with the grapes in the case of warm regions, for example, is that because the growing season is starting earlier, the, uh, roughly a month worth of ripening, uh, right before harvest is now shifting from say early fall/late summer, more into squarely being in summer. And that means relatively hotter ripening conditions. And since temperature can affect the quality and composition of grapes in many different ways, as you're thinking of acidity, sugar, some of the flavor and aroma compounds, uh, those types of things, which all are going to react to temperature, kind of on a semi-independent timestep, it's changing the nature of the wine.

Just from the simple fact of the growing season starting earlier. Acidity is coming in lower, sugars are coming in higher, higher sugars means more alcohol in the end product. And some of that can be attenuated in the winery, but still, the vast majority of what your wine ends up being is what comes out of the vineyard. And so some of these effects we're seeing already in climate change are impacting the quality and the composition of the wines that are ultimately produced. 

Emile: [00:03:18] Thank you. Kerri or Andy, did you want to add onto that?

Andy: [00:03:29] I guess I can say there's some advantages too. So one of the things you didn't want to do 20 years ago in Germany was drink a lot of red wine, because it wasn't very good. Again, it ripened too late. It wasn't in that window. And now with the warming conditions, which are literally, as Jeremy said, three, four weeks sometimes earlier than they have been in the past. Those varieties are ripening and there's a whole new effort to get more red wines into Germany and make that stronger and, there's some benefits here and there I guess, not many perhaps. 

And it's, it's opened up a whole new area of adapting to this early ripening cycle and getting things ripe in the middle of the summertime is one of the big problems, how do you avoid that? And in fact, in some of the tropical regions of the world, we can fruit grapes three times a year by careful pruning, irrigation, and fertilization practices.

The vines don't live very long, but they have, they can be tremendously productive. And two of those cycles are awfully, oftentimes just dropped on the ground. And they're not utilized for wine production or food production at all. Because they're timing the one cycle to a drier climate most of the time, drier and warmer in some situations as well to function that way. And we'll start playing tricks like that, through pruning, with cultivation in other parts of the world, too.

Emile: [00:04:49] Kerri, did you want to add anything?

Kerri: Yes, thank you, Emile. I think that what I'm observing in response to some of the increases in temperature are responses from the industry that are willing to try new practices that were less palatable even five to ten years ago. So, I've seen that there's increasing interest in using shade cloth in the canopy, looking at different kinds of material that can reduce the temperature.

That's a lot of labor that would have to go into that. It's an, it's an extra cost, but it looks like some research from the Department of Viticulture Enology at UC Davis is showing that it could be a way to decrease some of the heat load, um, depending on the price point for that particular operation.

And then another thing that I'm also observing is that there is increasing interest in using degraded waters for irrigation. So, some of the work that we've been doing is looking at how different kinds of saline waters can be used for irrigation and which soil types are more resilient or resistant to degradation from using these poor water sources from the winery or from other municipal effluent sources.

Andy: [00:06:03] That in fact, that what Kerri's mentioning is very interesting in the highly anticipated brackets, being able to use irrigation, water and a micro sprinkler sort of environment to cool, cool vineyards with evaporation. It has been done a lot in the desert already, and it's slowly marching its way North as the climate continues to fail.

But it's also sort of slow and hindered by the fact that the quality of water number one, and number two, it's evaporating on the leaves and it's damaging the leaves as well sometimes. So it's an interesting tradeoff that comes along.

Kerri: [00:06:40] Thank you. I wanted to ask Andy a follow-up question, if it's appropriate to discuss an anecdote about how they use irrigation water to force dormancy and bring grapes out of dormancy in table grapes. Is that a possibility for wine grapes or is that mainly a table grape practice? 

Andy: [00:07:00] Ah, if it changes that much and we get those temperatures in wine grapes we may be in bigger trouble. Maybe we should talk about Arizona again. Um, but yeah, I think it could be used and it could be, I think clearly is a more valuable tool in terms of timing and changing the cycle, the phenological cycles like it'll, it'll depend upon you utilizing more water though, oftentimes. Controlling growth more intensively, which will be problematic, too.

But yeah, water quality is one big component, and availability for that matter, right? So water is not getting any easier to find, it's environmentally and politically and environmentally largely regulated, and it should be, it's needed for everything. But one of the things that's not really needed on the planet is more wine in many ways. It's going to be hard to argue for a whole lot more water for wine grape viticulture in some spots. 

Sarah: [00:07:55] That's a perfect segue, Andy, to talk about future climate change. Right. And so we, you know, I guess the question is what kinds of future impacts might growers expect to see from climate change? And you, you touched on water availability, right?

So more severe droughts. I imagine that's going to become a concern. But maybe, you know, if you could speak to you know, could we expect to see changes to the types of wines produced? Right. If you know, certain regions, you know, will not become viable for grapes, certain grapes to be grown there anymore.

And then one more question to add on to that. And Andy, you touched on this too, but might there be any positive impacts of climate change as well? So I guess I'll just let anyone jump in really, if you wanna take a stab at that. 

Andy: [00:08:46] One of the components, I think is temperature. Again, we go back to that, and in this case it will be changing the way we have disease cycles and pests next to those diseases.

And one of the classic examples is Pierce's disease. So, uh, it's a bacterial disease from the Southern United States. It's very prevalent all through Mexico into Central America and it kills grapevines. There are very few diseases that kill grapevines outright. This is one of them. The other ones are much slower, more lingering, and eventually it kills them economically before it kills them physically. This is one that kills them physically. And interestingly enough, we've developed new varieties, that, five new varieties that have very strong resistance and pretty good wine quality. But getting them to the next step, which is marketing and promotion and all the rest is the tricky part and how people really use them. And it'll depend on what happens with Pierce's disease. It could get worse and it could get better.

And it depends really, probably mostly on rainfall. So if climate change is coincidental with drier conditions, that's going to be a very different scenario than climate change being coincidental with wetter conditions. And I don't think you can really predict at this point, particularly from the rainfall perspective, what's going to happen, which of those two scenarios are gonna play out together at the same time.

Sarah: [00:09:56] So Jeremy, how about, how about your work?

Jeremy: [00:10:05] The more and more I read about, climate change and viticulture in the coming decades, the more I realize the actual situation and how individual locations adapt to the changing conditions is going to be pretty complicated. We've been mentioning a lot of different aspects, a lot of different tools, adaptation tools that can come into play from canopy management, from pruning schedules, uh, to which varieties you're actually putting in the ground. Are they the top 10, 15 that we've been using for the past few decades? Or are they some of these other ones from the two to three thousand varieties that are out there that you're going to be using, and how well or how healthy they can remain under changing conditions is an open question. Uh, certainly when it comes from a grower's perspective, um, you're not going to want to tell them that it's not going to be viable there. And so you ought to be really sure you know that answer before you even approach it, uh, answering that question with the grower. But I think that, that, even though it overshadows the conversation, you know, is it viable or is it not?

Um, I don't think it's the topic or the topics that we need to be focusing on right now. I think a lot of these adaptation tools, diversity of approaches, they're going to be what we need to focus on right now in order to progress through the coming decades and try to give the industry as much as good of a chance of being successful as we can.

Emile: [00:11:51] That leads me to another question for Jeremy that actually pertains to everyone. And it's the question of climate analogs. So you're in Arizona and certainly most everything is irrigated there, I would imagine, but with some pretty high temperatures. And so it makes me wonder if there could be things that you're, that growers are learning in Arizona that could inform wine growing and wine production in California. Any thoughts on that? 

Jeremy: [00:12:24] Personally I think there's a big opportunity for Arizona viticulture on this subject. If you look at Europe, for example, where are they looking to as far as, as you put it, a climate analog? Where are they where they expect to be in 20, 30 years? Where is that today and where are they making wine and producing wine grapes?

Well, they're looking to Israel as an example. Uh, Australia is another one that serves as an example, right? I think Arizona viticulture, where they grow the vast majority of grapes in the state right now is at the warm and dry end of the spectrum of possible conditions under which you can grow wine grapes. And they have a big opportunity there to develop the knowledge, develop the technical capabilities, the management of the vineyards, the types of wines that are produced, what's done in the winery to produce a quality product under such hot, warm, and dry conditions. Uh, they really have a chance to be, be an example, uh, for these other regions that might be heading towards these hot, hotter and drier conditions. That we already have here. 

Sarah: [00:13:37] Kerri, do you have anything to add to what Jeremy and Andy have talked about with future climate change? 

Kerri: [00:13:45] Right now there's a large push to promote practices that can improve healthy soils, which is looking at the chemical, biological, and physical interactions in the soil to promote and support a productive agricultural system.

So climate analogs are useful in that context to understand what we can achieve or how the healthy soil might change in a future climate. And what kinds of metrics or what kinds of standards we might be able to achieve. So for example, I might look to the Paso Robles region to understand what dry hot conditions in California with limited water availability might look like for a soil environment.

And then if we know that those conditions will be present in 30 to 50 years in a wine grape growing region in Northern California, and I'm not saying that it will be, just as an example, that we would be able to help growers know what a reasonable standard would be, um, in that vineyard in 30 to 50 years. So that's how I would use climate analogs. If I, if I were with that.

Sarah: [00:15:00] Thanks, Kerri. So my next question here is for Jeremy. And Jeremy, you mentioned in part one that you and colleagues are working to make climate information more accessible to growers in order to better support their decisions that they have to make such as selecting sites and cultivars. So could you describe this project just a little bit more and maybe discuss ways that you're getting this climate information to the growers in Arizona? 

Jeremy: [00:15:31] I think to date, the climate viticulture work I've been doing has really been made up of two parts. And one of them has been establishing relationships with the growers, as well as with colleagues, uh, through some of the projects that I've been working on in the past couple of years under a few entities, like the Climate Assessment for the Southwest. So when I got started in the climate viticulture work, I actually didn't know anybody in the industry. And I don't think anybody in the industry knew me either. So it was a bit of a slow start and slowly but surely I got a toehold through presenting at and attending state viticulture symposia.

And from there, I've taken it in a direction where we have been able to now do growing season in review workshops. I have a monthly climate viticulture newsletter that I send out to growers that have subscribed. I've also developed relationships enough with some of the growers to where I'm working with them individually. Data analysis in some way, shape or form where we're putting together some type of climate information.

Sometimes it's in combination with data from their vineyard. Phenological observations, for example, what dates, when the growing season started, trying to answer the questions that they have as, as they go about the work in the vineyard from year to year. Another big part of the project so far has been continually asking myself, you know, putting myself in a growers shoes or winemaker shoes and continually asking myself, how is this piece of climate information going to help me with what I'm doing in the vineyard. And so it's really required me to learn a lot about vine phenology, learn a lot about vine physiology and even wine making, group quality composition, uh, to see what matters and to see where aspects of weather and climate like temperature really plug into the growing season and some of the decisions that growers are making in the vineyard. So even though that's taken a lot of extra effort, I think by framing the climate information in that way, in the context of vine phenology or physiology or fruit composition, I'm able to get that information that much closer to how a grower or winemaker’s actually thinking. And I think. In terms of what I do. Uh, that's a step in the right direction.

Emile: [00:18:17] Thanks Jeremy! Kerri, did you have something you'd like to add? 

Kerri: [00:18:22] I just would like to comment on Jeremy. That was a really nice description of how to engage with the industry. In my experience, working with growers is also trying to understand what's the entry point and what's the point that matters. And so when I began my career working in looking at the effects of vineyard floor management, on nutrient cycling and improvements in soil organic matter, and how you know, what the microbes are doing, I actually really didn't talk too much about that.

I wanted to understand. Um, well, the entry point was how do these practices reduce erosion? How do they affect water management in the vineyard? And then all of the other effects on soil health were just a side benefit and slowly for multiple reasons, both looking at the California Department of Food and Agriculture, Healthy Soils program, work by USDA, NRCS, and others at UC Davis.

And then just. There's a lot of focus right now on looking at how these management practices improve soil health. And so, uh, there's a lot of momentum there. So now that seems to be the main focus. But again, I think I liked the way that Jeremy phrased that you have to understand what matters to the growers and find the right entry point to start communicating and working with them.

So it's definitely a long-term relationship. And I would say that Andy is definitely, uh, can like, the proof is in the pudding. There's, there's Andy. You know, he's, he's got a great relationship with industry. And I think that, having been his neighbor next door at work, my office was next to his for a long time that I was able to see that on a daily basis.

Emile: [00:20:07] Thanks, Kerri. And that leads right into my next question of Andy, which is really, I feel like you have a strong and deep knowledge of viticulture in California. And I think that I would be curious about if we're missing some simple solutions. So I know those relationships with growers are really important, but, what have you seen over time? How was that knowledge built and for the industry and for growers, are we missing some simple solutions? I know we talked about shade cloth and irrigation, water and using more saline water, but what else might we be missing? 

Andy: [00:20:49] That's, that's a good question. Sort of sums it up and it comes back to the idea of diversity again and what we're missing is the varieties. We're missing utilizing things that've already adapted.

And there were the first thing our department did that's coming out of prohibition many years ago was evaluate hundreds of wine varieties for where they should grow best across the state. There's a massive work that was done by Amerine and Winkler, and others. It was just tremendous, and we've ignored it. 

So it really just said, which of these varieties will do best in which region, why will they do best? And it was doing basing that on phenological measurements and ripening, flowering dates, all the same sort of stuff. And we just shelved it essentially. And we've gone towards this path that has been largely directed by European marketing organizations.

It says that these 10, 15 varieties will be the best. And it's been sort of a countrywide decision of error and it's made viticulture marketing of viticultural products easier, but it hasn't really encouraged us to use the diversity we have available. So I think that that's easy enough to solve and easily done.

And I tell my students frequently that that viticulture is the most primitive form of horticulture that exists. We've made no advances in our plant material and we're happy about it. So it's, it's peculiar. And I think that climate change will really open the door to exploring this more effectively, thinking about, is it smarter to breed new varieties?

Which of course is the right answer if you're a grape breeder, or is it smarter to utilize what exists, and do a better job of characterizing how and why it exists where it is. So I think that's, to me, that's, climate change is going to be exciting, too bad I'm retiring. So it's, uh, it's one of those things that'll take another 10, 20 years to address from a breeding perspective, but it'll take at least that long to assess from a, just variety adaptation and relationship to soils. And rootstocks, we haven't talked about rootstocks at all, but they have a big role as well. 

Predation, all those things. I think the tools are already there and they're just waiting to be used. Which is the exciting news, it's not, it's not unfathomable that we can't approach it, there can't be a solution to this.

We're certainly going to be drinking wine still, but it will be different wine then, and I think that'll be positive overall. 

Emile: [00:23:01] Really positive, positive note to end on here, thinking about, you know, where, where to go from here, maybe how to expand the, what we currently grow and consume. And I wonder, you mentioned, we hadn't talked about rootstocks at all.

Did you want to share a bit about that before we close? 

Andy: [00:23:22] So there's two perspectives for rootstocks. One is controlling biotic problems, pest problems and disease problems. And we've been working on that. I've been working on that for more than 30 years and we're, we're moving towards the solution. There's also adapting to abiotic problems and those would be mostly water availability. And how do they tolerate drought? 

Salinity is, is coupled hand in hand  with drought and wherever we have Southwestern conditions, we're going to have salinity problems too. Uh, so as we use more water, we increase the salinity problem. We've recently found a species of grapes from the Red River of Texas that grow in 12% seawater.

So it's a pretty remarkable, they're actually physically not dying, but they're actually growing in those conditions. So the problem now is to turn that into a rootstock. Not only does it have to resist saline conditions, it has to tolerate both pest and disease in those situations. And it has to grow well enough to be propagated and generate more, more material from a nurseries perspective.

It's actually very complicated. Rootstocks, at first blush seem to be the simpler solution, but as you dig into them, there's so many different interactions that come into play that it's hard to keep them all in check sometimes. But it offers a good chance to address, particularly the drought and salinity issues I think are easily addressed through rootstocks over time.

A few of the others may be trickier. They also help phenologically, too. And they were selected originally for Northern European conditions or Southern European conditions. And it was mostly based upon targeting ripening and the extent of the growing season. And the adaptations to the rainfall in those areas.

So we have a lot of tools again, within the rootstocks, there are hundreds still available, and then we use fewer and fewer at the same perspective again. The corners, we stuck with the task of maintaining an inventory for people to buy and most years they don't buy it. So, um, the nurseries have been trying to winnow down that material as much as possible as well.

Emile: [00:25:23] Excellent. Well, thank you all for this glimpse into a pretty complicated and complex and fascinating industry and all of the different aspects or angles that you're approaching to address some of the challenges and to work with producers. And we're at the point where we look for any last thoughts.

So, Kerri, is there anything that you'd like to add that we didn't touch on? 

Kerri: [00:25:49] Thank you, Emile. Uh, my only final thoughts here that I'm really pleased to have met a new colleague Jeremy Weiss today, and also really happy that I live in the same town as Andy, so that when I have a question I can show up on his doorstep and ask him. So since I'll be working in this career for just a little bit longer. 

Emile: [00:26:10] Excellent, thank you, Kerri. Jeremy, any final thoughts?

Jeremy: [00:26:14] Well I'm certainly lucky and happy to have met Andrew and Kerri today. We have, some colleagues and I, have a two day workshop coming up from the State Viticulture Conference, probably in the fall, big asterisk there because of the pandemic, in which we're doing basically a variety evaluation, not a physical one out in the vineyard, but one where we're starting to get a list of, hey, what do we want to try? What are we already trying that's working well? What are we already trying that's not working well, what are we missing? 

And so now the conversation about all these varieties that are out there, the different rootstocks that are available, issues with the soil, all that's going to be I think, on the topic menu for that workshop now. And, uh, if you're wanting to attend, let me know, and we'll keep you in the loop as far as when and where it occurs. 

Emile: [00:27:14] Excellent. A lot of uncertainty out there, but something to look forward to. So thanks Jeremy. Andy, any last thoughts? 

Andy: [00:27:22] Maybe not. Although the, um, a lot of the things we're breeding for now are utilizing species from the Southwest. Particularly by this Vitis Arizonica, which curiously enough is from Arizona, it has remarkable characteristics, disease and pest and potential for the future as we go along. So maybe Jeremy and I will bump into each other on the hills and slopes of the various sky islands of Arizona and hunt down these grapevines because they're, they're plentiful, they’re all over the place in Arizona.

Kerri: [00:27:52] Andy, I just want to check in and make sure that you’re not jumping any fences still, to get that grapevine germplasm.

Andy: [00:28:01] I jump fewer fences as the years go on, so it’s getting a less pervasive activity. But I have my botanist license, so I show people, this is my botanist license.

Emile: [00:28:11] That might help in some situations I suppose. Well, thank you all so much for spending some time with us and talking about viticulture and giving us some information to think about as we go forward. And this concludes our podcast. 

Sarah: [00:28:30] Thank you everybody. 

Jeremy: [00:28:32] Thanks. That was fun. Good conversation. 

Emile: [00:28:34] Thanks for listening to Come Rain or Shine, podcast of the USDA Southwest Climate Hub 

Sarah: [00:28:40] and the DOI Southwest Climate Adaptation Science Center. If you liked this podcast, don't forget to subscribe like or follow for more great episodes. If you want more information, have any questions for the speakers, or would like to offer feedback, please visit or

Emile: [00:29:13] Our sincere thanks to USDA Agricultural Research Service, the Sustainable Southwest Beef project, and the US Geological Survey for supporting this podcast.