MEDITERRANEAN VITICULTURE IN THE CONTEXT OF CLIMATE CHANGE

The exposure of viticulture to climate change and extreme weather conditions makes the winemaking sector particularly vulnerable, being one of its major challenges in the current century. While grapevine is considered a highly tolerant crop to several abiotic stresses, Mediterranean areas are frequently affected by adverse environmental factors, namely water scarcity, heat and high irradiance, and are especially vulnerable to climate change. Due to the high socio-economic value of this sector in Europe, the study of adaptation strategies to mitigate the negative climate change impacts are of main importance for its sustainability and competitiveness. Adaptation strategies include all the set of actions and processes that can be performed in response to climate change. It is crucial to improve agronomic strategies to offset the loss of productivity and likely changes in production and fruit quality. It is important to look for new insights concerning response mechanisms to these stresses to advance with more effective and precise measures. These measures should be adjusted to local terroirs and regional climate change projections for the sustainable development of the winemaking sector. This review describes the direct climate change impacts (on phenology, physiology, yield and berry quality), risks, and uncertainties for Mediterranean


Climate change projections for the Mediterranean
The Earth's system is undergoing deep transformations owing to a strengthening of the anthropogenic forcing (Masson-Delmotte et al., 2021). Higher greenhouse gas concentrations in the atmosphere are dramatically changing the Earth's energy budget, with implications in the spatial patterns of weather and climate, as well as in their Article available at https://www.ctv-jve-journal.org or https://doi.org/10.1051/ctv/ctv20223702139 iência Téc. Vitiv. 37(2) xx-xx. 2022 140 temporal regimes. These changes are being manifested not only by significant warming trends worldwide but also by changes in precipitation and other atmospheric variables and climatic impact drivers, though with noteworthy spatial heterogeneities (Masson-Delmotte et al., 2021).
In Southern Europe and the Mediterranean Basin (MED region hereafter), along with the significant temperature increases, drying trends are also projected, thus explaining why this region is commonly considered a "climate change hot spot" (MedECC, 2020). Although changes in precipitation extremes, their probability of occurrence and intensity, are a global concern, the MED region is particularly exposed to a strengthening of dryness conditions. More frequent and severe droughts are projected for this region, with successive recordbreaking lengths of consecutive dry day episodes.
The projected warming and drying trends, together with an increased frequency and intensity of extreme weather events, are shown to be robust, particularly noteworthy in summer (Giorgi and Lionello, 2008;Lionello et al., 2014;Santos et al., 2020a;Tuel and Eltahir, 2020).
In MED, lower precipitation amounts combined with higher temperatures, lower cloudiness and higher solar radiation, will lead to an intensification of evapotranspiration and deficit water soil balances.
Water resources and availability will be threatened under these circumstances, exacerbated by a likely increase in water consumption from different sectors (e.g., energy and agriculture). Water competition is thereby expected to rise sharply in the upcoming decades, limiting water for agriculture, namely for crop irrigation, which is a practice that has been generalized throughout the MED region, even in traditionally rainfed crops.
Grapevine (Vitis vinifera L.) is a major fruit crop of economic importance worldwide (Macedo et al., 2021). In Europe, major wine-producing countries are located in MED. Italy (wine production of 49.1 mhL), Spain (40.7 mhL), Portugal (6.4 mhL) and Greece (2.3 mhL) jointly account for about 38% of the total global wine production, that is, 98.5 mhL out of 260 mhL (OIV, 2021). In 2020, these four countries exported approximately 10 000 million euros of wine. If several regions in southern France, also located in the MED region, are included, these values are even much more expressive. Viticulture and winemaking thus play a crucial role in the socioeconomy of these countries. However, viticulture is undoubtedly exposed and highly vulnerable to changing climates, as grapevines are very sensitive to both climate, which determines the suitability of a given location, and weather, which controls key plant physiological processes (Santos et al., 2020b). Atmospheric conditions govern grapevine phenology, growth and development, as well as grape berry quality parameters and wine attributes. These detrimental impacts can potentially threaten the regional wine characteristics and typicity, eventually altering the wine's regional suitability under future climates (Fraga et al., 2016a).
Therefore, climate change is a major risk for viticulture that requires adequate responses, by implementing sustainable but also cost-effective adaptation measures. However, mitigation strategies should also be envisioned to promote a transition to more resilient and carbon-neutral viticulture, also contributing to accomplishing international climate change policies, such as the Paris Agreement.
The present work will provide an overview of recent studies and developments concerning the climate change impacts and respective risks to viticulture (Section 2) and the corresponding available adaptation options for growers (Section 3) along with their discussion, and some concluding remarks (Section 4).
Therefore, rising air temperature alone could either delay or anticipate the budbreak, depending on the interactions between temperature response during the endo-dormancy and eco-dormancy phases . Furthermore, the inability to fulfil chilling requirements may strongly impact plant growth and development, ultimately affecting fruit quality and yield . In the northern hemisphere, budbreak commonly occurs between late winter and early spring. In anticipation of global warming, an earlier occurrence of budbreak by 7-11 days is projected for Spain, resulting from a stronger role of more intense thermal forcing accumulation than that of delayed chilling accumulation (Leolini et al., 2018). In addition, the late frost risk is reduced due to increased temperatures (Leolini et al., 2018).
Similarly, in Portugal, the projections for the Douro Demarcated Region (DDR) have depicted advancements of budburst by 6 days until the end of the 21 st century (Costa et al., 2019). Advanced budbreak with reduced spring frost risk is a likely outcome for many MED regions, whereas increased late frost risks around budburst are projected for western-central European countries (Sgubin et al., 2018;Droulia and Charalampopoulos, 2021).
For the flowering stage, a general advancement is also expected in MED regions. The 'Tempranillo' variety, accounting for ~50% of cultivating red grapevine varieties in Spanish vineyards, is projected to consistently undergo earlier flowering stages by 6-10 days, 3-8 days and 6-8 days in 2050, and 8-16 days, 5-12 days and 7-12 days in 2070, respectively in Ribera del Duero DO , Rioja DOCa (Ramos and Martínez de Toda, 2020) and Toro DO (Ramos et al., 2021). The earlier flowering stage is also accompanied by shortened phenophase in these regions, e.g. flowering-veraison and veraison-maturity (Ramos et al., , 2021Ramos and Martínez de Toda, 2020). Similarly, an anticipation of the flowering timing by up to 8 days until the end of the 21 st century is found for DDR under a moderate warming scenario (Costa et al., 2019;Reis et al., 2020). In some conditions, an advanced flowering stage can occur with higher temperatures and soil water deficits, consequently leading to reduced berry quality and/or yield at harvest (Fraga et al., 2016a,b;Mosedale et al., 2016).  (Mosedale et al., 2016;van Leeuwen et al., 2019;Santos et al., 2020b;Yan et al., 2020).

Physiology
Although it has been proven that vine is relatively resilient to summer stress (Schultz and Stoll, 2010), the presence of vegetative and reproductive symptoms driven by periods of severe dryness, occasionally intensified by heatwaves and/or excessive solar radiation, are indeed very frequent . This situation was verified with exceptional severity in the summer of 2022, largely exacerbated by scarce precipitation in the previous seasons and years, under a prolonged severe-toextreme drought episode.
Under these extreme conditions, characterizing the effective contribution of each environmental stressor is an unachievable task (Zandalinas et al., 2017).
Moreover, it was reported that their synergistic combination, compared to the response to each stress individually, may even worsen the deleterious impacts on grapevine physiological and oenological performance (Edwards et al., 2011;Bernardo et al., 2018). The effects of these summer stressors depend primarily on their severity (timing and duration) and the phenological phase affected .
From the fruit set until veraison, berry cell division can be seriously affected, impairing fruit size, berry weight and yield, due to a reduction of photoassimilates availability from veraison onwards (Duchêne et al., 2010, Parker et al., 2013. Likewise, prolonged periods of drought can also affect the initial stage of flowering and the accumulation of storage compounds essential for vines' longevity (Ollat and Gaudillère, 2000).
Stomatal closure is one of the most reported impacts of water deficit on plants, limiting photosynthesis, due to decreased CO 2 availability in the intercellular spaces (Schultz and Stoll, 2010 (Venios et al., 2020).
Preventing photo-inhibition and overheating of leaves can also be accomplished by changing leaf angles and leaf winding. These mechanisms help reduce the leaf's intercepted radiation and are mainly noticed under severe water deficits and high temperatures (Chaves et al., 2010). Similarly, leaves exposed to severe summer stress exhibit increased cuticle thickening, boosting not only the reflection of excessive radiation but also their drought resistance (Lovisolo et al., 2010). Some grapevine varieties, namely 'Perlette', can change their foliar angle between the limbus and the petiole from 53º to 80º when subjected to periods of drought, high temperature and radiation (Smart, 1974). The downregulation of photosynthesis can also be triggered by the Rubisco's unstable activity and regeneration during severe environmental conditions since its affinity to carbon dioxide can be impaired, leading to photo-respiration, and thus decreasing the synthesis of carbohydrates (Galmes et al., 2010). It was also reported that Rubisco activity, and consequently photosynthetic efficiency, is speciesdependent and mainly affected by water deficit conditions (Flexas et al., 1998, Bota et al., 2004, Zha et al., 2021. Nonetheless, in this context of low photochemical efficiency, in which high light and high temperature conditions can often exacerbate the damage of water deficit, the dissipation of nonradiative energy through the light-harvesting complexes (LHC) of PSII may represent the most effective protection mechanism against high solar radiation levels, temperature and drought (Palliotti et al., 2009, Villalobos-González et al., 2022. In addition, the activation of the xanthophyll cycle is paramount under these conditions, promoting photoprotection by improving the thermal dissipation of energy (non-photochemical quenching), preventing the production of reactive oxygen species, and increasing the thylakoid membrane tolerance to lipid peroxidation (Demmig-Adams and Adams, 2006, Dayer et al., 2019).

Yield and quality
The balance between vine development, growth and berry quality requires an optimal exposition of vines to mean air temperatures, typically ranging from 12 ºC to 25 ºC for the production of photo-assimilates, water availability over the growing cycle, and at least 700-900 μmol photons/m 2 /s of solar radiation (Arias et al., 2022). In Mediterranean-type climate viticulture, this balance is being compromised by the pace of climate change, causing yield losses and affecting berry composition and quality (Santos et al., 2020b). Although most European winegrowing regions may benefit from increased CO 2 concentrations that can partially offset dryness, resulting in higher yields, Southern Europe, particularly the Iberian Peninsula, are expected to experience productivity losses of up to 8 tons/ha due to severe water shortage , Fraga et al., 2016a.
Under warmer and drier conditions, the advancement effects on vine phenology, and the shortening of phenophases, associated with detrimental effects on photosynthesis and leaf area, can lead to decreases in biomass accumulation, and thus yield losses compared to longer growing seasons (Bernardo et al., 2018). Alongside, wine production is also expected to decrease by 20-26% in the forthcoming decades due to progressively warmer and drier conditions (Droulia and Charalampopoulos, 2021 Mozell and Thach, 2014;Pons et al., 2017). Within certain thresholds, sunlight exposition triggers the production of grapevine secondary metabolites, with a central role in the antioxidant defence system and wine quality potential (Cohen et al., 2008). For example, Sadras and Moran (2012) reported a delayed onset of anthocyanins accumulation in 'Shiraz' and 'Cabernet Franc' berries exposed to high temperatures after veraison, suggesting that stress exposure shortly before veraison could partially restore the anthocyanin/sugar ratio disrupted by enduring summer stress conditions.
Likewise, a wide range of specific metabolites for grapevine protection and berry quality against summer stress was also reported, such as shifts in the accumulation of osmoprotectants, carbohydrates, malic and tartaric acids, polyols, and amino acids (Suzuki et al., 2014, van Leeuwen andDestrac-Irvine, 2017). Associations with higher berry and must pH in grapevines exposed to high temperatures and drought conditions were also observed, though this relationship is affected by increased potassium accumulation, being also temperature dependent, particularly during the ripening phase (Coombe, 1987).
In berries, the combination of high temperatures, radiation, and drought can also impact the offset and decoupling of berry sensory traits through an acceleration of berry shrivelling and mesocarp cell death, with significant effects on berry size, and therefore a more substantial potential for increasing the concentration of phenolic compounds (Bonada et al., 2013). However, high temperatures trigger the degradation of berry anthocyanins that can limit, or even reverse, the positive effects of water deficit on wine's floral and fruity aromas (Bonada et al., 2015).

Uncertainties, modelling and policies
The risk assessment by modelling climate change impacts on the cropping system is crucial to provide information to policymakers and farmers . However, inherent uncertainties exist in  showing an enhanced ability to capture mesoclimates, regional weather patterns and extreme weather events at a local scale (Rummukainen, 2016). Therefore, coupling GCMs with RCMs is an essential tool to carry out the risk assessment of climate change impacts and the development of local-to-regional adaptation strategies.
This gives rise to model structure uncertainties, which need to be duly accounted for by utilizing an ensemble of GCM-RCM pairs/chains in climate impact assessment studies (Asseng et al., 2013;Tao et al., 2018;Yang et al., 2019). Nevertheless, systematic bias still exists in the outputs of GCM-  (Maraun, 2016). Depending on the variable and bias type, various methods can be applied. All of these methods intend to adjust specific statistical properties of the simulated time series toward observational time series (Cannon et al., 2015;Lange, 2019). Hence, the quality of the adjustment and the degree of bias reduction depends on both the method applied and the observation dataset used (Maraun, 2016). Furthermore, reducing the bias of one statistical property can also introduce errors into another property, or distort the physical consistencies between variables.
The uncertainties of simulated climate change impacts can also derive from how the cropping system is simulated. The process-based crop models are useful tools to capture the complex interactions among genotype × management × environment (Rosenzweig et al., 2013). Similar to GCMs/RCMs, uncertainties of applying these models mainly derive from their structure and calibration approach with fewer uncertainties arising from climate modelling (Asseng et al., 2013;Tao et al., 2018Tao et al., , 2020. Reducing the structural uncertainties should target experiments to gain insights into specific biophysical processes (Asseng et al., 2015;Rötter et al., 2018).
Applying crop models to a new environment often involve the calibration of some parameters to reflect local conditions (Rosenzweig et al., 2013, Seidel et al., 2018, Yang et al., 2017, 2020

Canopy management
It is well-known that agronomic strategies should be   (Santesteban et al., 2017). If harvesting goblet-trained vines could be mechanized, this would significantly reduce production costs for this otherwise drought-resistant training system (van Leeuwen et al., 2019). In terms of water dynamics, and comparing training systems, the adaptative potential to dry areas of Guyot-pruned vines (due to their shorter trunks) was also reported when compared to spur-pruned cordon . During the last decades, the main aim of the training systems was to increase the leaf photosynthetic efficiency, by increasing the leaf area and light exposure of grapes. But now, training systems should be reevaluated with reverse purposes: on the one hand, declining the water demand by reducing the leaf area while preserving a satisfactory sugar content in the fruits and, on the other hand, leaving the grapes in shade as much as possible (Duchêne et al., 2014)   The use of this foliar protector in the mitigation of some environmental stresses has been increasingly studied in recent years (Glenn et al., 2010;Brito et al., 2019;Frioni et al., 2019). Its effectiveness is related to the white protective particle film that is formed on the leaf's surface, which promotes the reflection of excess radiation  Frioni et al. (2020), in northern Italy, with 3% kaolin on VSP 'Pinot Noir' canopies, with fully exposed leaves, found 17% lower PAR and 50% higher PAR reflectance (Frioni et al., 2020). This strengthened reflection leads to a decrease in leaf temperature (Brillante et al., 2016;Dinis et al., 2018a). The   However, the amount of net CO 2 assimilation and transpiration rates vary among sites, vineyards plots, varieties and terroir. In Portugal, field-grown kaolin-coated vines of cv. 'Touriga Nacional' had shown consistently higher stomatal conductance rates, with leaf water potential ( Figure 5) between -0.7 and -1.5 iência Téc. Vitiv. 37(2) xx-xx. 2022 149 MPa at midday, compared to control vines, as well as higher net CO 2 assimilation rates (+58.7%) and intrinsic water use efficiency (iWUE) (Dinis et al., 2018a,b). Also in Portugal, the percentage of average change of gas exchange parameters of cv. 'Touriga Franca' kaolin-treated relative to untreated vines in a two-year study at two different winegrowing regions (Alentejo and Douro) showed the positive effect of this particle film, especially in very hot years (2017) compared to fresher ones such as 2018 (Bernardo et al., 2021a) - Figure 6.   (Dinis et al., , 2018b. Kaolin improved grapevine plasticity and ability to deal with prolonged periods of summer stress, optimising their capacity to control light absorption and manage the absorbed light (Bernardo et al., iência Téc. Vitiv. 37(2) xx-xx. 2022 150 2021b). Regarding carotenoids, (xanthophyll cycle, VAZ) the quantity of violaxanthin, neoxanthin and zeaxanthin (Vx+Nx+Zx) are augmented in kaolintreated vines, possible due to the reduction of abscisic acid (ABA) accumulation in treated leaves (Frioni et al., 2020). In drought periods, ABA synthesis is mandatory and indole-acetic acid (IAA) accumulation is limited in the guard cells leading to a deacrease in stomatal conductance due the stomatal closure (Dinis et al., 2018a). Under these conditions, it was found a reduction in ABA concentration in leaves sprayed with kaolin (Dinis et al., 2018a). The fruit cooling effect induced by the kaolin contributed to higher fruit quality    Ferrari et al. (2017) showed that in both 'Malbec' and 'Sauvignon Blanc' varieties no effect was noticeable.
The kaolin application could provoke a delay in maturation due to the shadow induced leading to higher organic acids concentration and total acidity as observed (Ferrari et al., 2017;Dinis et al., 2020).
Nonetheless, in a study with cv. 'Sauvignon Blanc', no changes were found in organic acids concentration, wine acidity and pH derived from kaolin-treated plants (Coniberti et al., 2013).  found a significant influence of kaolin in the grape metabolome, providing berries with high phenolic compounds, tartaric and malic acids, total acidity, and lower sugar content. A positive influence on wine was also observed, having higher acidity and lower alcohol levels, and also seems to have improved the aroma. Ferrari et al. (2017) obtained higher scores, given by experts, to wine (concerning typicity, aroma and body) resulting from kaolinsprayed plants.

Soil and water management
Cover crops are used to improve the soil structure and erosion control, and enrich nitrogen and organic matter content, while regulating the excessive grapevine vigour (Pardini et al., 2002). There are several positive impacts of soil organic carbon (SOC) in agroecosystems, such as enhancing soil structure (micro-and macro-aggregates) and cation exchangeability, improving infiltration, water holding capacity and preventing topsoil loss (Eynard et al., 2005). Cover crop root systems create vertical pores, enhancing the rate of infiltration and stabilising organic carbon-rich topsoil, whereas above-ground biomass reduces the dispersive impact of raindrops (Novara et al., 2019). A study carried out in Chile found that the introduction of leguminous cover crops (or combinations of them) increased soil nitrogen (N) to such an amount that they can supply grapevines with up to 40 kg N/ha (Ovalle et al., 2010). Marks et al. (2022) suggest a distinct managementbased approach to increasing SOC stocks by the sowing of cover crops in place of herbicide-managed bare earth. This approach seems to have a mechanistic benefit. It increases SOC as a function of inputs, such as root and shoots biomass, root exudates and microbial biomass as a function of atmospheric carbon (C) fixation and translocation (Peregrina et al., 2014). Both SOC stocks and labile organic C were increased in the presence of cover crops versus the traditional, herbicide-managed practice (Marks et al., 2022) Weber, 1980). Other studies found similar effects, but changes in the canopy architecture and decrease of the grapevine vigour and crop yield were only observed after several years (Gontier et al., 2011). In a four-year experiment carried out in France by Gontier et al. (2011), a reduced crop yield and vigour, and an increased sugar and phenolic content in grapevines under a complete grass cover cropping were noted. However, in North Carolina and for 'Cabernet Sauvignon' vineyards, Giese et al. (2014) found no depressive effect on productivity caused by complete floor covers.  found that cover crops reduced grape production by modifying yield components in different ways: legume mixture decrased the cluster weight, whereas grass mixture led to a lower number of clusters per vine along with lower cluster weight. Cover crops also influenced the must typicity. Grass mixture increased sugar, and polyphenols content, whereas legume mixture and natural covering caused a decrease in total polyphenols and anthocyanins contents, respectively.  suggest that the effects of cover crops seem to be mediated through nutrient availability and content in grapevines. Thus, using competitive cover crops, while reducing yields, can improve must quality.   (Courault et al., 2005;Ghiat et al., 2021).
For irrigation purposes, grapevine water requirements are usually estimated from the evapotranspiration of a well-known reference surface, typically a grass reference (Allen et al., 1998), and then related to crop evapotranspiration using specific crop coefficients. This variable corresponds to the use of the maximal value of ET, with adequate available soil water for optimum plant growth, under the climate and cultural practices considered.
Still, grapevine irrigation must be managed in such a way as to prevent severe water deficits, which may cause detrimental impacts at physiological and biochemical levels and high defoliation. On the other hand, it should not promote the dilution of berry metabolites and competition for excessive vegetative vigour (source-sink imbalance), as well as excessive shading of the bunches, especially during maturation (Magalhães, 2015). As an illustration, in the early iência Téc. Vitiv. 37(2) xx-xx. 2022 153 phenological stages (budburst to flowering), a degree of absent to very light water stress is recommended, while in post-veraison moderate water stress is required (Deloire et al., 2004). In this way, deficit irrigation strategies (regulated deficit irrigation, sustained deficit irrigation, and partial root-drying) have been implemented, sustaining yield and quality and increasing crop water use efficiency (Geerts and Raes, 2009;Chaves et al., 2010). These strategies should include soil (e.g. soil moisture) or grapevine water status indicators (e.g. leaf water potential) to define a threshold level of water stress (Mirás-Avalos and Araujo, 2021; Rienth and Scholasch, 2019). In addition, automated plant-based sensors (Cifre et al., 2005;Ferreira et al., 2012), geographic information systems and crop models are being used, optimizing precision irrigation, thus increasing water and energy use efficiency and vineyard profitability (Bellvert et al., 2020).

CONCLUDING REMARKS
This review highlights the effects of climate change on Mediterranean viticulture. After selecting the most tolerant varieties, selection of the training system is the primary measure to combat thermic and water stress, and facilitate better management of the plant's water use. After this measure, foliar protectors, coverings and even irrigation can help vines to improve their performance and consequently their yield quality. The possible adaptation strategies to cope with climate change still hold several uncertainties. Nevertheless, the adaptation strategies, duly adjusted to local terroirs and regional climate change projections, will contribute to the sustainable development of the winemaking sector, by providing guidelines for decision-making concerning the ongoing management of vineyards, but also for planning climate-smart vineyards in the upcoming decades, that is vineyards designed to better respond to climate change pressures. Not only stakeholders but also policymakers can play a key role in the required sectoral transformation, e.g., by designing appropriate and effective policies and regulations, at both the national and EU level, to facilitate the intended gradual transition of the entire wine production chain. This range of different strategies will contribute to a winemaking sector more resilient to climate change and its derived risks, but also more sustainable in the long-term, both environmentally and socioeconomically.