Abstract
Background and goals Southern California, an important producer of high-quality wines, continues to expand its grapegrowing areas, supporting livelihoods and contributing to thriving local economies. However, climate data indicate that the region is becoming increasingly warmer and drier, threatening future winegrape production. Grower perceptions of climate change and their vineyard management responses play a critical role in adaptive capacity but have not been well examined for this region.
Methods and key findings We used a survey to examine how grapegrowers in the South Coast American Viticultural Area perceive climate and climate impacts, as well as their adaptive capacity. Based on 71 responses, we found that growers have been observing fewer rain events (73%), more frequent heat events (63%), and earlier budbreak (32%) and harvest dates (41%) over the past decade. Growers reported implementing a variety of short-term adaptive practices such as canopy management, but fewer considered long-term anticipatory measures such as planting drought and heat tolerant varieties. Based on a logistic regression model, growers who showed greater concern about future climate impacts were more likely to report implementing adaptive strategies on their vineyard in the last five years (odds ratio = 5.314, p = 0.017). Lastly, many growers feel they do not have the support (34%) or resources (52%) necessary to implement adaptive strategies.
Conclusions and significance This survey revealed that growers in the region are experiencing a changing climate, some growers are already adapting to this change, and improved access to resources and support are critical for adaptive success. We identify a pressing need for collaboration and knowledge sharing between growers, academics, and local government agencies toward capacity building.
Introduction
Wine is one of the most popular alcoholic beverages consumed globally, with wine retail reaching $45.6 billion for the state of California in 2021, as found on the Statista website (https://www.statista.com/statistics/737296/california-wine-us-market-value/). However, the impact of climate change on global wine production is widely recognized (Merloni et al. 2018) and changes in climatic conditions can significantly affect wine productivity (Cahill et al. 2007), quality (Mira de Orduña 2010, Diffenbaugh et al. 2011), and economics (Ashenfelter and Storchmann 2010). Rising temperatures are expected to primarily affect regions at mid-latitudes, including a loss of suitable grapegrowing areas in both the United States (White et al. 2006) and globally, if adaptive measures are not taken (Diffenbaugh et al. 2011, Morales-Castilla et al. 2020). Indeed, heat accumulation can affect winegrape phenology, ripening (van Leeuwen and Darriet 2016), and yield potential (Keller 2010), and induces changes to biochemical composition (i.e., alcohol and acidity), flavor profile (Mira de Orduña 2010), and quality of the final wine product (Mozell and Thach 2014).
Sustained production of winegrapes in mid-latitude regions will require investment into new practices that help combat anticipated stressors. Many adaptive methods have been considered, including short-term strategies (e.g., changes to irrigation infrastructure [Fraga et al. 2018, Bellvert et al. 2021]), cooling techniques (e.g., misting and shading structures [Greer et al. 2011]), canopy management and training systems (Smart 1985), and long-term anticipatory strategies (e.g., planting heat tolerant varieties [van Leeuwen et al. 2019], changes to vineyard orientation and design [Grifoni et al. 2008], shifting cultivation areas to both higher altitudes and latitudes [Ausseil et al. 2021], and a combination of these strategies [Mosedale et al. 2016, Naulleau et al. 2021]). Humans have domesticated grapevines for thousands of years (Zohary and Hopf 2001), suggesting the evolution of cultivation practices in response to historical climate shifts. However, grower perceptions of modern climate change and how these perceptions play a role in adaptive vineyard management response, with either short- or long-term solutions, is not well understood.
Recent studies report that many growers have been perceiving climate change impacts and are implementing short-term adaptive strategies in various grapegrowing regions of Canada (Holland and Smit 2014), France (Neethling et al. 2017), Australia (Wheeler and Marning 2019), Germany (Bohnert and Martin 2023), Italy (Battaglini et al. 2009, Merloni et al. 2018), and Northern California (Nicholas and Durham 2012); similar analysis for Southern California is warranted. According to a recent climate analysis, the future of Southern California’s winegrape crop is under threat because of future climate changes (Monteverde and De Sales 2020). The regional temperature is projected to increase by 4 to 7°C by the end of the century, and heat waves and droughts are predicted to increase in frequency, intensity, and duration (Pierce et al. 2018), with predicted impacts to agriculture (Pathak et al. 2018). To our knowledge, this study is the first to examine climate change observations, perceptions, and vineyard management responses of grapegrowers in the South Coast American Viticultural Area (AVA), using both quantitative and qualitative social science approaches to assess adaptive capacity.
California contributes upwards of 80% of the U.S. wine production, employing 422,000 Californians and generating $73 billion in annual economic activity, as found on the National Association of American Wineries website (https://wineamerica.org/economic-impact-study/california-wine-industry/). The Southern California wine community has grown significantly within past decades, with 160 active and planned wineries in the county of San Diego alone, according to the California Department of Alcoholic Beverage Control (Vasquez 2022). The Southern California wine sector supports many livelihoods and contributes to the local economy, tourism, sales across the county, and exports. Despite the COVID-19 pandemic affecting both sales and employment, gross sales from local wineries in 2021 reached an estimated $44 million USD, a 19% increase from 2020 (Vasquez 2022). This highlights a wide interest in high-quality and locally produced winegrapes.
The major objective of this study was to increase our understanding of grower perceptions, observations, and adaptive capacity to a changing climate in the South Coast AVA. To address this objective, we asked the following research questions: What are growers’ perceived observations of decadal climate trends? What are the impacts of those trends on their crop? How are growers responding with vineyard management practices? Are growers equipped with the necessary knowledge and resources to better adapt to changes in climate?
Given current and projected future climatic conditions, the economic contribution of South Coast AVA vineyards to the local agricultural economy, and that this region is less studied than other major grapegrowing areas in California (i.e., Napa and Sonoma), the South Coast AVA is an ideal study area for addressing these questions. This study provides unique insights into climate trends and vineyard management practices that may help grapegrowing regions better adapt to climate change impacts, by providing policy-relevant information to decision-makers who wish to gain a better understanding of the status and needs of the winegrape growing sector. A goal for our findings is to help inform outreach and extension professionals, including government agricultural agencies, to better understand how they can assist growers in adopting long-term adaptations on their vineyards.
Theoretical Framework
Adaptive capacity has been defined as the ability of a system to modify its characteristics so it is better able to cope with existing and/or anticipated external stresses (Adger et al. 2003). The adaptive process can be complex, dynamic, iterative, and nonlinear (Quandt 2021). The adaptive capacity of an individual or community also takes place within the larger regional, national, and international contexts, where access to information and resources can vary (Adger et al. 2003, Quandt 2021). While these larger contexts are important for shaping adaptive capacity, it has been well documented that individuals often autonomously build their adaptive capacity based on their own perceptions, experiences, and conditions, as opposed to policy or government interventions (Quandt 2021).
Since individual viewpoints greatly influence decision-making (Slegers 2008, Tucker et al. 2010, Tanner et al. 2015), understanding how growers perceive climate change impacts is critical to studying their adaptation strategies. These views on climate change can be shaped by varying exposures, sensitivities to environmental shocks, personal experiences, and interpretations of the same climate signals (Kristjanson et al. 2017). Decisions about how to build adaptive capacity can be based on a person’s perceptions, knowledge, culture, and attitudes (Béné et al. 2016, Quandt 2019), and an individual’s perception may affect their ability and/or willingness to adapt (Béné et al. 2016). For example, in a study of smallholder farmers in Kenya, Quandt (2019) found that perceptions of resilience and adaptive capacity varied based on an individual’s gender and ethnicity. Thus, acknowledging the diversity of individual perceptions in climate change adaptation policy and in programs aimed to build adaptive capacity throughout the California agricultural sector could help establish feasible and long-term strategies (Singh and Chudasama 2017).
Materials and Methods
Study area and climate trend analysis
Our study area encompassed the broader San Diego County and southern Riverside and Orange Counties of Southern California. This includes the South Coast AVA and its respective sub-appellations, including the Temecula Valley, Ramona Valley, and San Pasqual Valley grapegrowing areas (Figure 1). This region is categorized by a Mediterranean climate, with cool and wet winters and warm and dry summers, as defined by the Koppen Classification system (Chen and Chen 2013). Vineyards that were not part of the previously mentioned AVAs but are located within the broader geographical limits of San Diego, Orange, and Riverside Counties were also included. While it is difficult to obtain data about how many growers are within the three focal AVAs, local reports indicate at least 40 growers in Temecula Valley, and at least 160 growers in San Diego County (Vasquez 2022).
The South Coast American Viticultural Area (AVA) and its respective sub-appellations, including the Temecula Valley, Ramona Valley, San Pasqual Valley, and the broader San Diego region. Size of circles represents the proportional number of responses received per sub-appellation. Blue lines on the California inset image indicate major waterways (rivers).
In addition, decadal climate trend analyses of the temperature and cumulative precipitation in this region were conducted to associate perceptions with actual observed climate data extracted from the Climate at a Glance County Time Series (https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/time-series). San Diego and Riverside Counties were chosen for the trend analysis because they encompass the prominent grapegrowing regions of Ramona Valley and Temecula Valley, respectively.
Survey
The structure of the largely close-ended survey was divided into the following sections: 1) demographic information, 2) vineyard descriptors, 3) climate trend observations, 4) climate impacts on vineyard, 5) vineyard management practices, 6) climate perceptions, and 7) knowledge and resource accessibility. Demographic questions included age, gender, race/ethnicity, education, location, employment, and years of experience, while vineyard descriptor questions asked about vineyard age, location, acreage, and grape varietals planted. Climate trend multiple choice questions asked growers to report any perceived changes in precipitation, drought, growing season temperatures, extreme heat events, frost days, and growing degree days (GDD) over the past 10 years. The climate impacts section focused on how these impacts might manifest in the vineyard, including effects on budbreak, harvest dates, wine acidity and alcohol levels, and pest and disease occurrence (multiple choice questions). Vineyard management questions aimed to capture what types of data growers are collecting and monitoring (multiple choice questions), as well as Likert-scale questions about decision-making when adopting adaptive practices and how growers are adapting vineyard management, based on perceived climate change impacts. Lastly, the climate perceptions and knowledge and resource accessibility sections mostly contained Likert-scale and Yes/No questions about access to resources, knowledge, and perceptions of climate change. Reported changes in vineyard management practice in response to climate impacts, access to resources, and feelings of preparedness to overcome climate change were used to assess perceived adaptive capacity through Likert-scale questions about these topics (mostly on a scale of strongly disagree to strongly agree).
The survey consisted of 64 questions (Appendix); to respect respondent time, increase response rates, and provide more reliable data, all questions were optional (Bernard 2017). In an attempt to encourage respondent comfortability, increase response rates, and promote honest responses and avoid social desirability bias (Bernard 2017), the survey format was anonymous. Survey questions were largely closed-ended, with a few instances where respondents could type answers to add detail.
Data collection and protocol
The population of interest consisted of individuals actively working, or with extensive experience, in viticulture management in the San Diego and/or Riverside Counties, and are directly involved in the production, operations, and management decisions of their vineyard. “Grower” is a common term used throughout the California agricultural sector to describe the farm manager, owner, and/or decision-maker. Thus, we use the term “grower” to describe our research participants. Recruitment started by identifying experts and other key figures in the wine industry, including leaders of relevant, well-established organizations (who remain anonymous, per Institutional Review Board [IRB] guidelines). A list of contacts was collected and compiled from publicly-available webpages. An email script was developed that explained the relevance and scope of the project and included a link to the survey. The recruitment announcement was then broadcasted via email to various organizations across San Diego County and southern Riverside County.
Through our outreach efforts, we estimate that this announcement reached over 200 growers. While there are likely more than 200 growers across the study area, reaching 200 growers means that we likely reached a large percentage of growers in the study region (Vasquez 2022). Thus, our survey reached the majority of growers in the region, helping to minimize bias in our sample. However, using email and group meetings as recruitment tools may have excluded growers who are not active in groups, or do not have publicly available email addresses.
The survey was available during the 2022 postharvest season between 13 Sept and 31 Oct. Responses were collected both online via the Qualtrics link and in-person by administering paper copies at organized meetings of viticultural associations such as the Ramona Valley Vineyard Association and the Small Winegrowers Association of Temecula. Data were collected and stored in a password-protected Qualtrics account accessible through San Diego State University. The survey was voluntary and approval from San Diego State University’s IRB (Protocol Number: HS-2022-0153) was obtained prior to administering the survey.
Data analysis
A total of 88 responses were recorded at the close of the survey. Of these, 17 incomplete responses were removed from the data, resulting in 71 responses for further analyses. The overall response rate of complete responses was 35%, consistent with average online and email response rates that can range from 10 to 30% (Bernard 2017). We are confident in our overall sample, as research has shown little connection between response rate and nonresponse bias (Hendra and Hill 2019).
Demographic information, dichotomous questions, Likert-scale questions, and other closed-ended questions were imported into Stata and Excel and quantitatively analyzed. Frequency analyses were used to interpret response variables as a function of demographic and vineyard descriptor data. Using a Kruskal-Wallis H test in Stata, we tested for any statistically significant differences between groups of growers who answered Yes, No, or Don’t Know, for a variety of questions about access to resources, preparedness, and adaptive strategies. These differences were tested against continuous variables such as vineyard size, years in current position, and age of vineyard. These variables may be important in shaping adaptive capacity, as more experience and a larger vineyard may provide growers with relevant knowledge and resources to implement adaptive strategies. For a post-hoc test, we ran the Dunn’s test to explore the specific differences between any two groups. For example, for any given variable, the Dunn’s test determines if the significant differences in the Kruskal-Wallis test are between the Yes and No groups, Yes and Don’t Know groups, or No and Don’t Know groups. A logistic regression model was also built to predict if perceptions of risk and concern about climate change impacts (Likert-scale questions) were likely to influence if a grower has implemented adaptive strategies in the last five years (Yes/No question). Lastly, open-ended responses were used to substantiate and/or provide reasons behind the quantitative results.
Results
Demographics and vineyard characteristics
Demographic information, experience, and vineyard characteristics (Table 1) were collected. More than a third of respondents ranged in age from 60 to 69 (36%) years old, while 25% were older and 38% were younger. The majority of respondents were white, while Latino, Black, and “other races” made up only 14% of the reported ethnicities. Specifically, more than half of respondents (60%) were white males. Some respondents (41%) reported taking on multiple roles, such as winemaking (30%), viticulture (17%), cellar master (11%), and administrative roles (10%). The experience level in winegrape production and vineyard management ranged from 1 to 28 years of experience, with 40% indicating 5 years of experience and 60% with 6 years of experience.
Respondent demographics and vineyard characteristics. SD, standard deviation.
Half of the respondents (48%) did not report their respective AVA or did not identify with a particular sub-appellation. Of those that did report their AVA, 49% were from Temecula, 43% from Ramona, and 8% from San Pasqual. However, all reported vineyards fell under the broader appellation of the South Coast AVA (Figure 1). Most vineyards (79%) were established in the last two decades and of those, nearly half (43%) were established within the last five years. Only 21% of vineyards were reported as being older than 20 years. The mean size of vineyards was 2.83 ha, with 90% reporting less than 4.05 ha. The study cumulatively represents ~210.44 ha of land used for winegrape production, based on reported growing area. The top three reported varieties grown were Cabernet Sauvignon (17%), Syrah (8%), and Sangiovese (8%), with Cabernet making up 31% of the total reported land area, Merlot and Sangiovese 13% each, and Syrah representing 6% of total land area. The remaining 37% was a mix of alternative varieties, each representing 5% or less of the total study land area.
Decadal climate trends
Climate trend graphs illustrate the annual average, minimum, and maximum temperatures (Figure 2A) and precipitation levels (Figure 2B) for San Diego and Riverside Counties over the past two decades (2003 to 2023). The mean temperature in Riverside County has increased by ~ +0.4°C/decade, while the minimum temperature has shown a sharper increase of +0.6°C/decade. The maximum temperature trend is +0.2°C/decade. San Diego County displays similar patterns, with a mean temperature increase of +0.3°C/decade, a minimum temperature rise of +0.4°C/decade, and a maximum temperature trend of +0.2°C/decade. For precipitation trends, San Diego County shows a slight increase in annual precipitation, with a trend of +15 mm/decade, while Riverside County shows a decreasing trend in annual rainfall of −18 mm/decade.
Annual average, minimum, and maximum temperatures (A) and precipitation levels (B) for San Diego County (SD) and Riverside County (R) from 2003 to 2023, using data extracted from the Climate at a Glance County Time Series (https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/county/time-series). San Diego and Riverside Counties were selected for the trend analysis because they encompass the prominent grapegrowing regions of Ramona Valley and Temecula Valley, respectively.
Perceptions of climate trends and the impacts on vineyards
Growers were asked about their observations regarding climate trends over the past decade, including temperature, precipitation, and extreme weather events (Figure 3). A majority of growers have observed a decrease in the number of rain events (73%), and more frequent (62%) and intense (30%) drought events in the past 10 years, as well as more frequent extreme heat events (63%), which have increased in intensity (28%). Many growers also observed the average climate getting warmer (66.2%), and an increase in the number of GDD (28.2%) in the last decade. However, a larger proportion of respondents indicated that they “don’t know” or observed “no change” (46.5%) in the number of GDD. In general, these perceptions are aligned with the weather data presented in Figure 2A, which highlights increased temperature.
Grower perceptions of changes in climate over the last 10 years, listed by five or more survey respondents. Bars show number of respondents, with numbers indicating percentage of respondents.
Growers were also asked about observed changes in grapevine phenology, as well as final yield and chemistry of grapes produced on their vineyard (Figure 4). About a third noted earlier budbreak (32%) since the last decade, as well as an earlier harvest (41%), while none (0%) reported a later harvest. When growers were asked in an open-ended question what they attributed to the shift in budbreak and harvest dates, 20 respondents alluded to warmer temperatures as the cause, using words such as “heat”, “hot”, “warm”, and “temperature”. However, many also reported more variable harvest (34%) and budbreak dates (21%). According to the open-ended responses, many growers attributed changes in budbreak to warmer temperatures, prolonged heat events, increased heat waves and drought conditions, and more heat earlier in the day. One respondent explained that the increase in variability observed is a result of “site to site variability” due to “differences in soil type and climate exposure”. When asked about grape and wine characteristics, a third of growers indicated that neither wine alcohol levels (34%) nor acidity had changed (24%). Indeed, only a few reported higher (14%) and lower (15%) wine alcohol and acidity levels, respectively. When asked why changes were observed, growers often stated that any changes to wine alcohol and acidity were a result of the amount of “heat exposure”, but often “varied by variety”. Those who detected increased alcohol levels often attributed it to temperature. More extreme and prolonged heat is consistent with higher sugar and alcohol levels. Those who noticed changes in acidity reported that heat spikes and warm nights, especially after veraison, lead to less acid.
Grower perceptions of changes in wine characteristics and vineyard plants over the last 10 years, listed by 10 or more survey respondents. Bars show number of respondents, with numbers indicating percentage of respondents.
Qualitative results from the open-ended responses demonstrated that growers saw vineyard management practices as an important variable for grape chemistry outcomes. For example, growers commented that vineyard management may often be the cause of these shifts such as, “earlier pruning producing earlier bud burst”. Furthermore, some growers indicated that harvest dates are carefully chosen based on a combination of grape indicators including “pH and Brix”, that “harvest dates are chosen to compensate for the warmer temperatures”, and that “vineyard practices” were an important factor in determining the final grape chemistry and timing of harvest. Many growers reported constantly adapting their vineyard management in response to climate, reporting that growers “do what [they] need to do to make things work. Sometimes [they] fail and then try again.”
More frequent pest and disease occurrences in the past 10 years were reported by 24% of growers. However, in their open-ended responses, several growers acknowledged that pest management efforts on their vineyard had an important role in observed changes in pest and disease frequency and occurrence. For example, pests were observed to be “less frequent due to [implementing an] aggressive vineyard management plan”, and “better pest management” and “vineyard practices” were cited as causes of observed changes in pest and diseases.
Growers were asked to report which stressor posed the greatest threat to grape yield and quality, as well as the financial impact to their vineyard (Figure 5). Growers indicated that heat stress was the most critical stressor for wine quality (37%), followed by pest damage (18%) and water stress (14%). However, water stress was reported as the greatest threat, particularly for its yield and financial impacts (28% and 31%, respectively). This was closely followed by heat stress and pest damage for both yield and financial impacts, respectively.
Grower perceptions of the greatest stressors on wine production and vineyard outcomes, divided by area of greatest perceived risk.
Vineyard management
Next, growers were questioned about the types of data collected on their vineyards and whether that information was used to determine and/or adapt their vineyard management practices (Figure 6). Only 41% actively monitored the microclimate on their vineyards. Of those that reported collecting climate data on their vineyards, the top variables collected were ambient temperature, soil moisture, precipitation, and wind speed (47, 37, 37, and 30%, respectively). If microclimate data were being collected, many growers (38%) applied this information to determine and/or adapt their vineyard management choices (Figure 6).
Survey questions pertaining to grower perceived adaptive capacity.
Growers were also asked whether they observed and/or collected data on grapevine growth, health, stress, and water status. Nearly half of all growers (48%) collected stress indicators such as stem water potential, canopy temperature, and greenness. This was followed by growth indicators (41%) (e.g., leaf area index, trunk growth, and canopy size) and health indicators (e.g., chlorophyll content) as the third most collected information (34%). Of those who collected data on their vines’ performance, 73% used this information to make management choices on their vineyard. However, (35%) reported not collecting plant performance indicators at all. One grower reported that “owners need to be willing to invest in effective solutions, but usually are hesitant to make changes that are costly”.
Similarly, 76% of growers somewhat/strongly agreed (i.e., “somewhat” or “strongly”) that the total amount of rainfall was an important factor in determining irrigation management decisions. Moreover, 63% of growers were concerned about access to irrigation water in the next 10 years. However, only 27% reported collecting water use indicators (i.e., stomatal conductance, transpiration, and water use efficiency) on their vineyard, despite high reported drought observations in the past decade and water stress reported as one of the greatest threats to wine production.
Perceptions of climate change and adaptive capacity
Survey questions regarding perceptions of climate change and perceived adaptive capacity were designed to provide broad responses, primarily through Likert-scale and Yes/No questions. When asked whether the impacts of climate change have been positive or negative, over 60% of growers claimed the impacts have been somewhat or extremely negative, and a similar proportion (62%) were concerned about the future impacts of climate change. This surprisingly did not reflect the proportion of growers that reported climate adaptive strategies on their vineyard (42%), and less than a quarter of respondents (20%) reported planting drought and/or heat tolerant varieties on their vineyards (Figure 6). Of those that reported implementing adaptive practices, the most frequently reported practices were changes to canopy management, changes to soil management for perceived improved water holding capacity, and improving irrigation efficiency (77, 59, and 52%, respectively).
Despite high reported concern regarding climate change impacts, less than half of growers (47%) felt they were prepared to overcome climate change related challenges on their vineyard, and a little over half (56%) reported having access to reliable information to inform themselves about the impacts (Figure 6). Still, some growers (34%) felt they did not have adequate support to adapt their vineyard to climate change, and about half (52%) did not feel well-equipped with the tools and resources required to overcome climate related challenges (Figure 6).
Additionally, it is important to understand the interplay of perceptions of climate change impacts and metrics of adaptive capacity. To understand the influence of climate change perception on whether a grower reported implementing adaptive strategies in their vineyard in the last five years (a Yes or No question), a logistic regression model was conducted. In Table 2, the only significant predictor of implementing an adaptive strategy in the last five years was high levels of concern about anticipated impacts of climate change on the vineyard, which had an odds ratio of 5.31 and a p value of 0.017. Thus, higher levels of concern about climate change impacts led to growers being more likely to report implementing adaptive strategies.
Logistic regression model of the relationship between growers reporting to have implemented adaptive strategies on their vineyard in the last five years, and questions of their perceptions of broad climate change impacts. Questions of climate change impacts were formatted as 5-point Likert-scale questions. Odds ratios, standard errors, p values, and 95% confidence intervals are shown. Respondents that did not answer any of the questions and those who answered “I don’t know” were excluded from this data (i.e., n = 47).
In Table 3, we also compared questions focused on perceived adaptive capacity (Yes/No/Don’t Know questions) and vineyard and/or grower characteristics such as vineyard size, years of experience in current position, and age of vineyard (continuous variables). A growers’ level of experience in years (continuous variable) was an important factor in whether adaptive management practices were implemented in their vineyard (Table 3). In our post-hoc tests, we found significant differences between growers who answered “Yes” or “No” and those who answered “Don’t Know” (Dunn’s test p values for both were equal to 0.01) (continuous variable). Therefore, while growers with more experience were not significantly more likely to have implemented adaptive strategies in the last five years, they were more likely than growers with less experience to know that they have not implemented these strategies (Dunn’s test p = 0.002). Our analysis also found differences between these demographic variables and if a grower had planted drought and/or heat tolerant grape varieties in the past five years. For example, growers with larger vineyards were more likely to have planted drought and/or heat tolerant grape varieties than those who have not (Dunn’s test p = 0.042). Interestingly, growers with more years of experience in their current position were more likely to have not planted drought and/or heat tolerant grape varieties (Dunn’s test p = 0.02). Lastly, age of vineyard was important and on average, growers managing older vineyards were more likely to know if they have (Dunn’s test p = 0.009) or have not (Dunn’s test p = 0.0028) planted drought and/or heat tolerant varieties.
Measures of perceived adaptive capacity compared with grower and vineyard demographics as independent variables. The data shown represent the median number of respondents, with standard deviation in parentheses.
Discussion
Climate perceptions and impacts
The observed trends in increasing temperatures and variable precipitation from the past two decades align with grower perceptions of increasing drought and temperature extremes in the region. These climatic changes can stress grapevines, affect grape quality, and necessitate adjustments in vineyard management practices. For instance, the rise in minimum temperatures could alter phenology and grape maturation cycles, while precipitation patterns could affect irrigation strategies and water resource planning. Most growers were concerned about climate change impacts and agreed that it has negatively affected their vineyard and threatened winegrape production. Our survey results are similar to studies conducted in Europe that also show warming trends (Battaglini et al. 2009, Neethling et al. 2017).
Our results indicate that growers in our study area are observing climate change impacts on grapevine phenology as well—particularly an advanced growing season with budbreak and harvest dates shifting earlier, as well as more variability across years and between grape varieties, which is also supported in the literature (Parker et al. 2013, Cameron et al. 2021). Based on both quantitative and qualitative responses, growers attributed the shift in earlier harvest date to the warming temperatures observed in the past two decades. This coincides with existing literature on advanced phenology observed across the globe (Jones 2003, Cook and Wolkovich 2016), as well as evidence of temperature strongly correlated with earlier phenology in regions such as Europe (Droulia and Charalampopoulos 2022), Australia (Webb et al. 2012, Jarvis et al. 2019), and Northern California (Nemani et al. 2001, Cayan et al. 2023). Importantly, our survey is the first documentation of this type of phenological change (earlier budbreak and harvest), and its link to warming trends, in winegrapes in Southern California.
Despite this inference, some growers were concerned that their vineyard management choices played a very important role in observed vineyard impacts and changes, as opposed to climate change and climate variability alone. Thus, the interplay between climate and grower vineyard management response is likely deeply intertwined in wine-grape production. Particularly, changes in pest and disease occurrence, rather than climate change, were often attributed to pest management practices that were implemented in that respective growing season. This demonstrates the added complexity of perceiving and understanding climate change impacts based on vineyard observations and encourages the implementation of long-term viticultural field trials with a goal to understand the effects of climate stressors on vineyard management.
Adaptive capacity
Our findings show that some growers in the study area have been perceiving changes in climate, are observing the impacts of those changes on their vines, and are taking action to adapt to those changes. Battaglini et al. (2009) found that growers who perceived an impact of changing climatic conditions on their winegrape production were more likely to be interested in implementing adaptation strategies. Results from the current study help us understand growers’ adaptive responses to a changing climate, which is critical to improve interventions, policy, and extension efforts (Singh and Chudasama 2017). To adapt to heat and water stressors, growers in our study implemented practices such as improved irrigation methods, canopy management changes, and soil management changes to improve water holding capacity. Incremental, short-term adaptive strategies such as these are common among farmers both within and outside the study area because they operate within the existing socio-biophysical context and utilize resources that are already available (Adger et al. 2003, Quandt 2021). Research in France found growers implementing similar short-term adaptation strategies such as soil management practices (Neethling et al. 2017), and an interview-based study in Northern California found that growers took a reactive approach to addressing climate stress, with few formulating short-term anticipatory vineyard management solutions (Nicholas and Durham 2012). Thus, future research should focus on identifying strategies that help growers effectively build adaptive capacity to the impacts of climate change, based on both current experiences and long-term climate change projections.
Although short term and reactive strategies may help mitigate current water and heat stressors facing grapevines, more transformative change may be necessary in the long term. While 42% of respondents have implemented short-term strategies, only 20% reported planting more drought or heat tolerant grape varieties in their vineyards, and these growers reported having significantly larger vineyards by area. Thus, external resources such as available land can heavily influence adaptive potential and grower willingness to take risks. Some growers in Europe are also planting more drought and heat tolerant varieties (van Leeuwen and Darriet 2016, Koufos et al. 2020). Similar to our study, Neethling et al. (2017) found that changing grapevine varieties were adopted as “last resort” adaptation strategies. Moreover, 84% of the growing area reported in this study was represented by merely 10 varieties (Cabernet Sauvignon, Merlot, Sangiovese, Syrah, Vermentino, Grenache, Zinfandel, Sauvignon blanc, Chardonnay, and Cabernet franc). Increasing phenotypic diversity on the vineyard (Wolkovich et al. 2017, Morales-Castilla et al. 2020) and identifying new rootstock-scion combinations (Duchêne 2016) has increasingly been considered as a method to buffer against the impacts of climate change.
Perceived climate risks are critical in shaping individual grower adaptation decisions, as people generally act based on their perceptions (Slegers 2008, Tanner et al. 2015, Béné et al. 2016). Importantly, growers in our study who reported greater concern about climate change were generally more likely to have taken some adaptive measures and felt more prepared to overcome potential challenges. Our results highlight how an individual's perception of the same climate signal may vary and affect willingness to adapt (Béné et al. 2016, Kristjanson et al. 2017). Similarly, a study in Italy concluded that perception of negative impacts of climate change were a determining factor in whether growers implemented adaptation practices (Merloni et al. 2018).
A third of the vineyards in our study area are less than five-years-old, and there is an increase in the amount of land used for grapegrowing. This is in-line with an economic report showing a 6% increase in active and planned wineries from 2021 to 2022, and a $3 million increase in estimated gross sales from 2018 to 2021 (Vasquez 2022), suggesting that growers may be switching from other crops to wine-grape production. While the reasons for the recent growth in winegrape production are likely complex, factors like economic opportunities, climate change impacts on water efficiency, and vineyard management practices may play a role.
We found that growers managing smaller and younger vineyards, and growers with less experience, were faced with greater uncertainty about the adaptive potential of their vineyard management practices. Growers with less experience felt unsure whether they implemented adaptive management practices on their vineyard. These same growers, as well as those managing younger and small-holder vineyards, were unsure whether their established varieties were drought and/or heat tolerant. Additional outreach, resources, and support may assist these growers to understand their current vineyard management practices, as well as other vineyard management practices that will help them adapt to climate change impacts. As reported elsewhere (Tucker et al. 2010), adaptive responses may be associated with external factors, such as access to land, versus perceptions.
Our study was largely composed of smallholders (80% of respondents managed less than 2-ha vineyards) and amateur growers (34% with less than five years of experience), a demographic that is highly vulnerable to climate change (Harvey et al. 2014). Many growers in our study also reported lack of knowledge and experience and feeling uncertain about the impacts of climate change on their vineyard. This knowledge and resource disparity creates important challenges where climate change impacts may disproportionately affect growers that are new to the industry. To promote overall climate resilience of the region, there is a need for collaborative efforts that encourage knowledge sharing across experience levels. Despite these limitations, most growers expressed positive attitudes, such as confidence, to overcome the potential challenges posed by a changing climate, a desire to learn and adopt new practices, and a willingness to collaborate with research and academic institutions, all of which can influence perceived adaptive capacity (Seara et al. 2016).
Identifying barriers to adaptation
Information, resources, and experience are important elements of adaptive capacity development (Brooks and Adger 2005). Based on our study, many growers in the South Coast AVA are still uncertain about the general trends and future impacts of climate change. This indicates that knowledge about climate science may not be clearly and consistently disseminated to the broader community. Thus, scientists and academics could expand their efforts to engage with grapegrowers, and those in other agricultural sectors, to effectively present the most current climate science, as climate communication strategies have been a topic of debate for many years (Moser and Ekstrom 2011). A recent study found that increasing climate data transparency and accessibility promoted trust between academics and growers, ultimately leading to the consideration of long-term adaptive agricultural management practices, rather than short-term (Babin et al. 2022). Future interventions could focus on developing climate data tools (Palutikof et al. 2019) and fostering respectful conversations to stimulate debate and deliberation (Pearce et al. 2015). Hopefully, knowledge sharing, transparency, and reciprocity between scientists and growers will enhance the local grapegrower climate science knowledge base.
In our study, although some growers generally felt confident they could overcome the challenges of climate change, many growers, particularly amateur and small-holders, felt that they lacked adequate resources and support to do so. Lack of access to resources, reliable information, and external support is an important barrier to adaptive potential, suggesting that the implementation of outreach and extension programs should be developed with amateur growers and smallholder vineyards in mind. Such programs should focus on cross-collaboration with academic institutions and across disciplines, supporting participatory science that lowers barriers to knowledge, and promoting resource accessibility toward adoption of more resilient and sustainable vineyard management practices.
Based on our results in San Diego and Riverside Counties, California, we propose two policy recommendations that may apply to other major global grapegrowing regions. First, improved vineyard management strategies and climate change adaptation should work in tandem to create a new framework for building adaptive capacity. As many growers in our study were unsure if changes in their vineyards and wines were due to climate change or management practices, a combined approach may address these uncertainties. For example, promoting policies and resources that help growers monitor soil moisture and vineyard microclimate may lead to new soil and water conservation practices that not only improve vineyard management more generally, but also help with adapting to increasing heat or water stressors in the vineyard due to the impacts of climate change. Second, efforts should not rely on the decisions of one individual or entity, but should strive for collective decision-making across organizational boundaries (Mosedale et al. 2016). For instance, academic and/or research institutions and cooperative extension programs should foster relations with grapegrowing associations and groups via iterative engagement and dialogue regarding vineyard management and adaptation strategies. In our work, many growers felt they did not have access to resources and knowledge, and a collaborative approach may help address this concern.
Conclusions
The impacts of climate change on winegrape production are being observed at a local, regional, and global scale. Southern California has an ideal climate for winegrape production but is experiencing a warming and drying climate trend at an unprecedented rate. To date, little is understood how climate change impacts growers and their operations and how they have responded to ongoing climate challenges. This study finds that grapegrowers in the region are perceiving climate shifts in the past decade, particularly the frequency of extreme weather events such as increasing droughts and number of extreme heat days. The impacts are being noted in the vineyards with changes to phenology, particularly earlier budbreak, as well as earlier and more variable harvest dates, depending on varietal. Growers are often responding to stress with short-term vineyard management strategies, while anticipatory practices that aim to address ongoing or future potential climate change impacts are less common. With many young and emerging vineyards in Southern California, it is even more imperative to ensure growers have access to the knowledge and tools they need, and that vineyards are being established with high adaptive capacity. Additional studies, including follow-up interviews, are needed to better identify grower limitations toward adopting long-term sustainable and adaptive strategies (e.g., access to climate information, vineyard monitoring tools, planting of climate suitable varieties and rootstocks, implementation of efficient irrigation systems, and information sharing). A thriving grapegrowing sector will require the development of anticipatory vineyard management practices and standards, in cooperation with academics, local government agencies, and appropriate stakeholders, to ensure future Southern California wine production is sustainable and resilient.
Supplemental Data
The following supplemental materials are available for this article in the Supplemental tab above:
Appendix: Local winegrowing trends and adaptation to climate change
Footnotes
The authors thank the following associations for their collaboration and help in distributing the survey to their members; Ramona Valley Vineyard Association, Temecula Valley Winegrowers Association, Small Winegrowers Association of Temecula, and the San Diego County Vintners Association, as well as all survey participants for contributing their time and experience to this study. A.Z. acknowledges the NOAA Educational Partnership Program with Minority Serving Institutions (NOAA-EPP/MSI), and the Center for Earth System Science and Remote Sensing Technologies (NOAA-CESSRST-II) for fellowship support under award #NA22SEC4810016. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of NOAA. Lastly, the authors acknowledge the Joint Doctoral Program in Ecology at San Diego State University with the University of California Davis for additional financial support. This research was approved by the Institutional Review Board (Protocol Number: HS-2022-0153). The authors declare that they have no relevant competing financial or non-financial interests that could have influenced the work reported in this research article.
Zuniga A, Monteverde C and Quandt A. 2024. Grapegrower perceptions of climate change impacts and adaptive capacity in Southern California. Am J Enol Vitic 75:0750021. DOI: 10.5344/ajev.2024.24031
All data underlying this study are included in the manuscript and its supplemental information.
By downloading and/or receiving this article, you agree to the Disclaimer of Warranties and Liability. If you do not agree to the Disclaimers, do not download and/or accept this article.
- Received May 2024.
- Accepted August 2024.
- Published online September 2024
This is an open access article distributed under the CC BY 4.0 license.
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