Int J Biometeorol DOI 10.1007/s00484-012-0617-8 ORIGINAL PAPER Future scenarios for viticultural zoning in Europe: ensemble projections and uncertainties H. Fraga & A. C. Malheiro & J. Moutinho-Pereira & J. A. Santos Received: 26 July 2012 / Revised: 7 November 2012 / Accepted: 2 December 2012 # ISB 2013 Abstract Optimum climate conditions for grapevine growth are limited geographically and may be further challenged by a changing climate. Due to the importance of the winemaking sector in Europe, the assessment of future scenarios for European viticulture is of foremost relevance. A 16-member ensemble of model transient experiments (generated by the ENSEMBLES project) under a greenhouse gas emission scenario and for two future periods (2011–2040 and 2041–2070) is used in assessing climate change projections for six viticultural zoning indices. After model data calibration/validation using an observational gridded daily dataset, changes in their ensemble means and inter-annual variability are discussed, also taking into account the model uncertainties. Over southern Europe, the projected warming combined with severe dryness in the growing season is expected to have detrimental impacts on the grapevine development and wine quality, requiring measures to cope with heat and water stress. Furthermore, the expected warming and the maintenance of moderately wet growing seasons over most of the central European winemaking regions may require a selection of new grapevine varieties, as well as an enhancement of pest/disease control. New winemaking regions may arise over northern Europe and high altitude areas, when considering climatic factors only. An enhanced inter-annual variability is also projected over most of Europe. All these future changes pose new challenges for the European winemaking sector. Electronic supplementary material The online version of this article (doi:10.1007/s00484-012-0617-8) contains supplementary material, which is available to authorized users. H. Fraga (*) : A. C. Malheiro : J. Moutinho-Pereira : J. A. Santos Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), University of Trás-os-Montes e Alto Douro (UTAD), PO Box 1013, 5001-801 Vila Real, Portugal e-mail: [email protected] Keywords European viticultural zoning . Bioclimatic indices . Climate change . Ensemble projections . Viticulture . Model uncertainties Abbreviations CompI Composite index DI Dryness index ECA&D European climate assessment and dataset GCM Global climate model GSP Growing season precipitation GSS Growing season suitability HI Huglin index HyI Hydrothermal index IPCC International panel on climate change MOS Model output statistics NIQR Normalized interquartile range RCM Regional climate model TR Total range SRES Synthesis report on emission scenarios Introduction Climate plays a predominant role in grapevine growth (e.g. van Leeuwen et al. 2004; Santos et al. 2011), as vine physiology and its development phases are determined mostly by specific environmental conditions (e.g. Magalhães 2008). In fact, monthly mean temperatures and precipitation totals in the growing season present significant correlations with grapevine yield in many regions (e.g. Makra et al. 2009; Santos et al. 2012a). Grapevine is a heat demanding crop, requiring a 10 °C basal temperature for its growing cycle onset and development (Amerine and Winkler 1944; Winkler 1974), and Int J Biometeorol relatively high solar radiation intensities (e.g. Magalhães 2008). However, prolonged exposure to excessive heat (e.g. temperatures above 40 °C) may have detrimental impacts on some physiological processes (Berry and Bjorkman 1980; Osorio et al. 1995), resulting in poor yields and quality (Kliewer 1977; Mullins et al. 1992). Although grapevines are also resistant to relatively low temperatures (lower thermal lethal limit of approximately −17 °C) during early stages (Hidalgo 2002), frost occurrences during spring can severely damage crop production (e.g. Spellman 1999). Further, excessive humidity in spring can trigger pests and diseases, such as downy mildew (Carbonneau 2003), while severe dryness during the growing season can also lead to harmful water stress (Koundouras et al. 1999) thus leading to reductions in grapevine productivity (Moutinho-Pereira et al. 2004). Given these considerations, climate change brings new and major challenges for winegrape growers. In fact, projected future changes over Europe under the A1B International Panel on Climate Change (IPCC) – Synthesis Report on Emission Scenarios (SRES) scenario (Nakićenović et al. 2000) include a temperature increase of 2.3–5.3 °C in northern Europe and 2.2–5.1 °C in southern Europe by the end of the twenty-first century (Christensen et al. 2007). In addition, for the same scenario, it has been shown that temperature extremes are also expected to increase throughout Europe (Andrade et al. 2012). Changes in inter-annual variability and extremes in climatic factors result in shifts in grapevine phenology, disease and pest patterns, lower predictability and regularity of the yields and wine quality (Schultz 2000; Jones et al. 2005a), being thus an additional pitfall for the winemaking sector. Conversely, benefits coming from the increase in CO2 concentrations under future atmospheric conditions may also play a key role in grapevine physiology and yield attributes (Moutinho-Pereira et al. 2009), though this forcing is out of the scope of the present study. Taking this climatic forcing into account, current grapevine global geographical distribution is limited largely to regions where the growing season mean temperature (April– September in the Northern Hemisphere) is within the 12– 22 °C range (Jones 2006). Taking the aforementioned delicate balance between environmental conditions and viticultural zoning into account, climate change is likely to have considerable regional impacts not only on grapevine attributes, but also on wine quality (e.g. Jones and Davis 2000; Jones et al. 2005b). Due to the high socioeconomic relevance of the winemaking sector in many European regions, the assessment of the impacts of climate change on viticulture is of the utmost importance, particularly for the most renowned winemaking regions spread over the continent. Winegrape growers are indeed becoming increasingly aware of these changes and their resulting impacts (Battaglini et al. 2009). Future climatic zones are then expected to shift polewards, leading to changes in the current regions suitable for grapevine growing and to new potential winemaking regions. In addition, due to the projected decrease in the annual precipitations over southern Europe (Christensen et al. 2007), grapevines are also expected to be affected negatively by severe dryness (Koundouras et al. 1999; Santos et al. 2003). Several studies in different areas of research used ensembles of model runs in assessing climate change projections under anthropogenic radiative forcing. As simple illustrations, Lobell et al. (2006) used a set of regional climate models to assess the impacts of climate change on perennial crop yields in California, while Heinrich and Gobiet (2011) used an 8-member ensemble for future projections of dry/ wet spells in Europe. The use of multi-model ensemble projections enables quantification of numerical model uncertainties arising from differences in physics and modelling approaches, model parameterizations and initialisations, among others. This is important because model uncertainty may lead to different outcomes (Deser et al. 2012). Another advantage of this approach is that multimodel ensembles commonly outperform studies based on projections from a single model (Knutti et al. 2010). Besides using statistical methodologies for model validation/calibration, enabling correction of model bias, quantification of the uncertainty associated to climate change projections may be as important to the winemaking sector as the climate change signal itself. The present study assesses potential changes in the suitability of a given region for winegrape growth in Europe under human-driven climate change. For this purpose, several bioclimatic indices, specifically developed for viticultural zoning, are applied using datasets from a 16-member multi-model ensemble under the A1B emission scenario for 2011–2040 and 2041–2070 (future periods). Hence, this study is structured as follows: (1) a multi-model ensemble is used for assessing climate change projections in a set of viticultural bioclimatic indices, (2) a validation with a stateof-the-art observational gridded daily dataset is conducted and calibration techniques are then applied to the model outputs, (3) the ensemble projections and the corresponding model uncertainties are analysed, (4) an analysis based on a categorized Composite Index (CompI) is carried out, and (5) the projected changes in the inter-annual variability are assessed. In the next section, the bioclimatic indices are defined, model data is presented, model output statistics (MOS) and model uncertainty are discussed. In the “Results” section, after an initial model skill intercomparison, the bioclimatic indices are presented, along with their inter-annual variability. An analysis of each individual model of the 16-member ensemble is also performed, depicting the cost of using single models versus the use of Int J Biometeorol model ensembles. In the final section, the main outcomes of this study will be summarized and discussed. Materials and methods Bioclimatic indices The implications of climate change on viticultural zoning in Europe were assessed on the basis of projections for the following bioclimatic indices: Huglin Index (HI; Huglin 1978), Dryness Index (DI; Riou et al. 1994), Hydrothermal Index (HyI; Branas et al. 1946), Growing Season Suitability (GSS; Jackson 2001) and Growing Season Precipitation (GSP; Blanco-Ward et al. 2007). The mathematical definitions of all these indices, as well as their main references, are listed in Table 1, and will not be further detailed here. Following two previous studies (Malheiro et al. 2010; Santos et al. 2012b), an improved CompI is also computed in the current study. The CompI at a given location is the ratio of “optimal years” for winegrape growth over a given time period to the total number of years in the period. An “optimal year” must simultaneously fulfil the following criteria: (1) HI ≥ 900 °C; (2) DI ≥ −100 mm; (3) HyI ≤ 7,500 °Cmm; and (4) total absence of days with minimum temperature below −17 °C. This new CompI differs from the previous definitions in the first and third thresholds (cf. Malheiro et al. 2010; Santos et al. 2012b). A lower HI threshold (900 instead of 1,200 °C) is considered herein in order to include viticultural regions in northern Europe with marginally suitable winemaking conditions. In fact, in two previous studies by Jones et al. (2010) and Hall and Jones (2010), a Winkler Index (WI; Winkler 1974) above 850 °C was found to be already suitable for winegrape growth in western United States and Australia, respectively. Additionally, (Santos et al. 2012b) showed a clear correspondence between the WI and HI patterns in Europe using 850 °C and 900 °C as lower limits, respectively. The threshold in the third criterion of the CompI (HyI≤7,500 °Cmm) was chosen so that only climatic conditions noticeably favourable to pests/diseases in the vineyards are excluded. Furthermore, when considering a lower threshold (e.g. 5,100 °Cmm), many winemaking regions in central Europe become misleadingly unsuitable (Santos et al. 2012b). In order to better discriminate the optimal climatic requirements of different winegrape varieties (Jones et al. 2005a), an innovative category analysis of the CompI is also carried out. At each site, the CompI is first classified as a function of three pre-defined HI classes , namely: 900≤HI< 1,500 °C; 1,500≤HI<2,100 °C; 2,100≤HI<3,000 °C. Then Table 1 List of bioclimatic indices used for climatic viticultural zoning in Europe, along with their corresponding definitions and references. The calculations (summations) are carried out using daily climate variables Bioclimatic index Definition Units Suitable threshold Reference Growing season suitability (GSS) Ratio of days with T≥10 °C °C - Jackson 2001 mm - Blanco-Ward et al. 2007 °C > 900 Huglin 1978 °C mm <7,500 Branas et al. 1946 mm >−100 Riou et al. 1994 Growing season precipitation (GSP) Sept: P ðPÞ April P Precipitation (mm) Huglin index (HI) Sept: P April ðT 10ÞþðTmax 10Þ d 2 T Mean temperature (ºC) Tmax Maximum temperature (ºC) d Length of day coefficient Hydrothermal index (HyI) Aug: P ðT P Þ April T Mean temperature (ºC) P Precipitation (mm) Dryness index (DI) Sept: P ðWo þ P Tv EsÞ April Wo Soil water reserve (mm)a P Precipitation (mm) Tv Potential transpiration in the vineyard (mm) Es Direct evaporation from the soil (mm) a Wo should be equal to 200 mm at the beginning of the growing season. For the following months, Wo takes the value of the DI in the previous month Int J Biometeorol the leading HI category is identified an assigned to the site. HI values below 900 °C are considered unsuitable for winegrape growth while values above 3,000 °C are relatively rare in Europe (not shown). This analysis allows a varietydependent assessment of the climatic change impacts on the viticultural sector. Model data Climate models remain a valuable tool in climate change assessments (Solomon et al. 2011), despite their widely reported limitations (e.g. Knutti et al. 2008; Hulme and Mahony 2010), and are used here as a source of information about future climate change, namely in the temperature and precipitation fields in Europe. Regarding the definitions of the selected bioclimatic indices (Table 1), daily mean, maximum and minimum 2-m air temperatures and daily precipitation totals are used in their calculations. These four daily atmospheric variables were extracted from datasets of 16 state-of-the-art transient experiments generated by the EU-FP6 project ENSEMBLES (http:// ensembles-eu.metoffice.com; van der Linden and Mitchell 2009), in a total of 15 different Global Climate Model / Regional Climate Model (GCM/RCM) chains (for the ECHAM5/COSMO-CLM combination, two ensemble simulations are used). Table 2 lists the 16 model experiments, along with their acronyms and main references. Only these 16 transient experiments provide records without data gaps in the two selected future periods (2011–2040 and 2041–2070). However, they provide a sufficiently representative sample of models, with different parameterisations, spin ups, physics and modelling approaches, covering a large amount of the uncertainty inherent to numerical model simulations. The A1B IPCC-SRES scenario (2001–2100), which corresponds to a moderate anthropogenic radiative forcing (Nakićenović et al. 2000), was used. Other SRES emission scenarios, such as A2, are not available for all ensemble members and were therefore not considered for the present analysis. However, the A1B and A2 scenarios start to clearly diverge in their emission pathways only from 2070 onwards (Nakićenović et al. 2000), later than the aforementioned two future periods. Daily model data was also extracted for the 40-year baseline period (C20; 1961–2000) so as to validate/calibrate it using an observational dataset. The daily station-based gridded dataset (E-OBS, version-4) from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com), provided by the European Climate Assessment & Dataset (ECA&D) project (http://eca.knmi.nl) in the baseline period, was used for this aim. The original gridded data is defined over land areas at 201 grid boxes along latitude and 464 grid boxes along longitude (0.25° latitude×0.25° longitude grid). This dataset, despite some limitations, represents a valuable resource for climate research in Europe (Hofstra et al. 2009). Detailed information about the E-OBS dataset can be found in Haylock et al. (2008). The baseline period (1961–2000) corresponds to the longest available common time-series amongst the different datasets (observations and simulations). All model datasets were bi-linearly interpolated (in latitude and longitude) from the original rotated grids (cf. their original spatial resolution in Table 2) to a regular grid of 0.25° latitude×0.25° longitude to enable model validation/ calibration using exactly the same grid as in E-OBS. Only the geographical sector [35-60°N; 12°W-36°E] where viticultural zoning is relevant is considered herein (102 grid boxes along latitude×190 grid boxes along longitude). The selected bioclimatic indices were then computed for all grid points with available data (excluding blank/missing data) in the E-OBS (11,506 grid cells). Statistically significant differences at a 99 % confidence level (using the two-sample Student’s t-test) between the future period of 2041–2070 and the baseline period for HI, DI, HyI and CompI were also computed and plotted. Model output statistics and model uncertainties Several studies have demonstrated that equal weights are generally a better approach than performance-based weights for computing ensemble mean statistics (Christensen et al. 2010; Weigel et al. 2010). For this reason, only equally weighted ensemble mean patterns for 2041–2070 (higher greenhouse gas forcing) are presented henceforth. However, an inter-comparison of model performances in reproducing the observed mean patterns of the selected bioclimatic indices in the baseline period (1961–2000) was undertaken in order to summarise and highlight the most important deviations (bias) between simulated and E-OBS mean patterns. Scatterplots representing the different models as a function of their spatial mean bias (MB) and absolute spatial mean bias (AMB; less sensitive to extremes then the root mean square deviation) in the HI, DI and HyI patterns are shown as supplementary material (Fig. S1). Due to the model bias referred above, MOS are used to fit raw model data to observations, as the statistical distributions of the simulated data present biases with respect to observations (Wilks 2006). This is also a common procedure when assessing climate projections (Mearns et al. 2001). Linear transfer-functions are applied to obtain transformed (adjusted) data with the same mean patterns as the observational data. Taking into account the large number of grid boxes (11,506), higher order polynomial, exponential or logarithmic transformations were not tested. This is not a clear shortcoming, mainly because the bioclimatic indices are defined on a yearly basis and most of them are normally distributed, according to the Lilliefors test applied to all indices and simulations (not shown); only a few exceptions Int J Biometeorol Table 2 Summary table of all Global Climate Model / Regional Climate Model (GCM / RCM) model chains used in this study. The corresponding acronyms, institutions and original grid resolutions are also listed. In all simulations the period 2011–2070 was used under the IPCC-SRES A1B scenario. References relevant to each chain are also indicated Acronym GCM RCM Original grid Institution References ARP Aladin(CNRM) ARP HIRHAM(DMI) BCM RCA(SMHI) ARPEGE-RM5.1 ARPEGE BCM CNRM-Aladin DMI-HIRHAM SMHI-RCA 25 km 25 km 25 km CNRM DMI SMHI EH5 RACMO(KNMI) EH5 CLM1(MPI) ECHAM5-r3 ECHAM5-r1 KNMI-RACMO2 COSMO-CLM-1 25 km 18 km KNMI MPI-M EH5 CLM2(MPI) ECHAM5-r2 COSMO-CLM-2 18 km MPI-M EH5 HIRHAM(DMI) EH5 RCA(SMHI) ECHAM5-r3 ECHAM5-r3 DMI-HIRHAM SMHI-RCA 25 km 25 km DMI SMHI EH5 RegCM(ICTP) ECHAM5-r3 ICTP-RegCM3 25 km ICTP Gibelin and Deque 2003 Christensen et al. 1996 Kjellström et al. 2005 Samuelsson et al. 2011 Lenderink et al. 2003 Böhm et al. 2006 Steppeler et al. 2003 Böhm et al. 2006; Steppeler et al. 2003 Christensen et al. 1996 Kjellström et al. 2005 Samuelsson et al. 2011 Elguindi et al. 2007 Pal et al. 2007 EH5 REMO(MPI) ECHAM5-r3 MPI-REMO 25 km MPI-M HC CLM(ETHZ) HadCM3Q0 (normal sens) ETHZ-CLM 25 km ETHZ HC HC HC HC HadCM3Q0 (normal sens) HadCM3Q16 (high sens) HadCM3Q3 (low sens) HadCM3Q3 (low sens) HC-HadRM3Q0 HC-HadRM3Q16 HC-HadRM3Q3 SMHI-RCA 25 25 25 25 HC HC HC SMHI HadCM3Q16 (high sens) C4I-RCA3 25 km HadRM3Q0(HC) HadRM3Q16(HC) HadRM3Q3(HC) RCA(SMHI) HC RCA3(C4I) were identified over some mountainous areas (e.g. the Alps). The linear transformations were then applied to the yearly bioclimatic indices, at each grid box, and for each model dataset individually. The transfer-functions between indices calculated from E-OBS and indices calculated from the models were estimated for the 40-year baseline period (1961–2000). This scaling procedure has been used in previous studies (Alexandrov and Hoogenboom 2000; Santos et al. 2012a; Fraga et al. 2012; Jakob Themeßl et al. 2011) and enables the correction of biases in the model simulations, also enabling a comparison between the different RCMs. As such, for 1961–2000, the corrected data of each index are equal amongst the different simulations and equal to the corresponding E-OBS data. Therefore, for the baseline period, only results obtained using E-OBS are presented. The same transfer-functions (coefficients) were applied to all datasets in the two future periods (2011– 2040 and 2041–2070), leading to corrected patterns for future conditions. In this procedure, the temporal invariance of the transfer-function between recent-past and future is a km km km km C4I Jacob and Podzun 1997 Jacob 2001 Steppeler et al. 2003 Jaeger et al. 2008 Collins et al. 2011 Collins et al. 2011 Collins et al. 2011 Kjellström et al. 2005 Samuelsson et al. 2011 Kjellström et al. 2005 Samuelsson et al. 2011 basic underlying assumption. In any case, it must be kept in mind that the patterns of the mean differences between a future period and the baseline period (climate change signal) are independent of these corrections. Also, applying transfer-functions to the indices and not to the original climatological data is a new methodology that may require further research. Measuring model uncertainty is also crucial when assessing future impacts of climate change. For this purpose, the 16-member normalised interquartile range (third quartile minus first quartile divided by the mean at each grid point; NIQR hereafter) of the HI, DI, HyI and CompI is also assessed and plotted. The spatial correlations of the CompI between the 16 simulations and the ensemble mean are also presented so as to clarify the spatial coherence amongst them. Inter-annual variability As previously stated, irregularity in the yields and wine quality is an additional pitfall for the winemaking sector. Int J Biometeorol Significant alterations in the inter-annual variability could lead to large economic impacts for this perennial crop. The ratios between the averages of the 16 inter-annual standarddeviations (calculated for each of the 16 ensemble members separately) in 2041–2070 and 1961–2000 of the bioclimatic indices (HI, DI and HyI) are computed to assess changes in inter-annual variability. Results Recent-past viticultural zoning The HI has been shown to be an effective tool for viticultural zoning and has been thus widely applied (Jones et al. 2010). Its ensemble mean pattern (Fig. 1a) is highly coherent with the GSS pattern (not shown) and highlights the fact that large areas of southern and central Europe are suitable for winegrape growth, whereas regions northwards of the 53°N parallel are generally unsuitable. In this context, it should also be emphasised that different classes of the HI are related to grapevine varieties with different thermal requirements (Huglin 1978). Hence, lower values do not necessarily mean lower suitability, but rather conditions that might be optimal for specific varieties (e.g. white grapevine varieties are generally favoured by cooler climates; Duchene and Schneider 2005). The mean patterns for DI and HyI (Fig. 1b,c) give opposite perspectives of the humidity requirements for optimal grapevine development. Severe dryness (assessed by the DI) and excessive humidity (assessed by the HyI) during the growing season commonly have detrimental impacts on the different stages of the grapevine development (Branas et al. 1946). Overall, the DI pattern depicts a remarkable contrast between southern Europe and central and northern Europe, and shows that dryness might be a limitation only over small areas of southern Europe and in certain years (values below −100 mm), whilst excessive humidity levels (HyI above 5,100 °Cmm) are generally restricted to Atlantic coastal areas or to mountainous areas, such as the Alps or the Carpathian range. The baseline period mean pattern for the CompI (Fig. 1d) demonstrates this index’s usefulness in viticultural zoning, since it is coherent with the spatial distribution of well-known traditional viticultural regions, showing higher suitability in the southern European areas. Composite index vs viticultural regions As mentioned in section “Bioclimatic indices”, the CompI is an attempt to characterise the most relevant atmospheric requirements for winegrape growth with a single index. According to our analysis, areas characterised by values of the CompI in excess of 0.5 (50 % of optimal years) in the period 1980–2009 encompass the most worldwide famous winemaking regions in Europe (circles in Fig. 1e), which are located mostly over southern and central Europe, particularly in countries such as France, Italy, Spain, Portugal and Germany). This attests to the utility of this index for European viticultural zoning. The more recent period 1980–2009 was chosen because it more closely reveals the present time atmospheric conditions reflected in current winemaking regions. As E-OBS data, used for model calibration, is available for 697 out of a total of 754 winemaking regions, only the former regions are taken into account (most of the missing regions are islands or coastal areas). From these 697 regions, about 93 % present a CompI equal to or above 0.5, i.e., are in agreement with the CompI pattern. Future viticultural zoning The HI patterns for the future period (Fig. 2a) shows a northward displacement and a stronger increase over southern and Western Europe. This reveals an apparent northward extension of the high suitability areas for 2041–2070. In fact, new suitable regions for grapevine development within the latitude belt 50-55°N are projected to arise, which is in line with the results obtained for GSS (not shown). Furthermore, important changes over southern Europe should also be expected under anthropogenic radiative forcing. For the DI in the future period (Fig. 2b) there is a significant drying over most of the southern half of Europe, which is in agreement with the projected changes in the GSP (not shown). These changes are likely to yield severe dryness (DI<−100 mm) in areas such as southern Iberia, Greece and Turkey. On the other hand, the projected changes in the HyI (Fig. 2c) reveal an enhancement of the humidity levels over central and eastern Europe, explained largely by the joint effect of warmer and moister conditions in the future (increase in the GSP and in the growing season temperature). Therefore, while dryness may represent a threat/challenge for winegrape growth in southern Europe (e.g. harmful water-stress), excessive humidity in central and eastern Europe can potentially trigger pests and diseases in the vineyards (e.g. outbreaks of downy mildew disease). The ensemble mean pattern for the CompI (Fig. 2d) reveals a general decrease in suitability in southern European regions, especially due to the increased dryness in these areas. Conversely, large areas of central and Western Europe are projected to become more suitable for viticulture, due to the more favourable thermal conditions. Climate change signals and uncertainties When assessing climate change projections, it is important to analyse not only the climate change signal itself, but also Int J Biometeorol Fig. 1 a Huglin Index (HI), b Dryness Index (DI), c Hydrothermal Index (HyI) and d Composite Index (CompI) for the baseline period (1961–2000). e European wine regions (circles) with the corresponding CompI value (cf. scale) for the period of 1980–2009 using the E-OBS data. Source of the wine regions locations: Wine Regions of the World—Version 1.31 (URL: http://geocommons.com/ overlays/3547) Int J Biometeorol Fig. 2 As Fig. 1 but for the future period of 2041–2070 under the A1B IPCC-SRES scenario the respective model uncertainties (Deser et al. 2012). The spatial correlations for the CompI pattern among the 16members and their mean (Table S1) shows that most models are clearly inter-correlated, as well as with their ensemble mean (correlation coefficients above 0.7). The models showing higher correlations with the ensemble mean are the ARP HIRHAM (DMI), EH5 REMO (MPI), HC CLM (ETHZ) and HC HadRM3Q0 (HC). On the other hand, the models showing lower correlations are BCM RCA (SMHI) and EH5 RegCM (ICTP). CompI maps for the models with the lowest (HC RCA3 (C4I); Fig. 3a) and highest (HC RCA (SMHI); Fig. 3b) spatial means of this index are also presented. Although their spatial patterns may show important differences, they are considered as equally probable in the present study (equal weights in the statistical measures). To assess the ensemble variability in the future projections (uncertainty) for the CompI in 2041–2070, some statistical measures [means, medians, minima, maxima, NIQR and total ranges (TR)] are provided in Table 3 for a selection of well-known grapevine growing regions throughout Europe. The means reveal CompI values always higher than 0.80 but for two regions (Alentejo-Borba, Tokaj-Hegyalja; cf. Fig. 2d), the medians are consistently higher than the means, which reflects the negative skewness of the distributions (CompI upper limit of 1.0). The minima show a large variability, with values ranging from 0.00 (TokajHegyalja) up to 0.99 (Champagne), while the maxima are always 1.00, with only two exceptions (Alentejo-Borba, Tokaj-Hegyalja). Regarding the ranges of variability, since TR is more affected by extremes than NIQR, some discrepancies between them are apparent; a higher TR does not necessarily imply a higher NIQR or vice-versa. Considering TR as an uncertainty measure, some regions reveal more pronounced uncertainties (Rheinhessen, Ribera del Duero, Chianti, Porto/Douro, Barolo, La Mancha, Alentejo-Borba, Tokaj-Hegyalja), whereas others present relatively low uncertainties and CompI minima above 0.70 (Champagne, Coteaux du Loire, Bordeaux, Mosel, Rioja, Rheingau, Vinhos Verdes, Alsace). The HI, DI, HyI and CompI climate change signals (difference between the ensemble means for 2041–2070 and 1961–2000) are now presented, along with the corresponding NIQR (Fig. 4). The latter is adopted as a measure of the model uncertainties. The significant increases in the HI values over most of Europe (left panel Fig. 4a) is associated with a relatively low uncertainty (right panel, Fig. 4a), with the exception of northern Great Britain and the Alps. Conversely, the changes in the DI pattern (left panel Fig. 4b) show large uncertainties, particularly in the regions where changes are most pronounced (the Mediterranean basin; right panel Fig. 4b). The HyI shows Int J Biometeorol Fig. 3 a Composite index (CompI) of the more severe model [HC RCA3 (C4I)]. b CompI showing the less severe model [HC RCA (SMHI)], for the time period 2041–2070 significant increases in eastern, northern and central Europe, while important decreases are found over southern and western Europe (left panel Fig. 4c). For this pattern, low uncertainty levels are displayed all across Europe (right panel Fig. 4c). Contrary to the DI, this index combines temperature with precipitation and its lower uncertainty is thereby also influenced by temperature. The CompI undergoes significant increases over large areas of northern, eastern and central Europe, whereas decreases can be found in some areas of southern Europe, mainly southern Iberia, southern Italy and Greece (left panel Fig. 4d). This index reveals high uncertainties in many eastern European regions (right panel Fig. 4d), where the strongest climate change signal is found, changing from recent-past climate conditions mostly unsuitable for viticulture to much higher suitability in the future. In these circumstances, slight differences in the climate conditions and/or projections tend to become very significant, in relative terms. Table 3 Ensemble means, medians, minima, maxima, normalised interquartile ranges (NIQR) and total ranges (TR) of the Composite Index (CompI) in 2041–2070 and for a selection of European famous winemaking regions (the respective grid box coordinates are also listed). Regions are ranked in ascending order with respect to their TR values Country Region Longitude/ latitude (º) France France France Germany Spain Germany Portugal France Germany Spain Champagne Coteaux du Loire Bordeaux Mosel Rioja Rheingau Vinhos Verdes Alsace Rheinhessen Ribera del Duero 4.003/ −0.846/ −0.055/ 6.734/ 2.402/ 7.944/ −8.545/ 7.6592/ 8.254/ −4.465/ Italy Portugal Italy Spain Portugal Hungary Chianti Porto/Douro Barolo La Mancha Alentejo-Borba Tokaj-Hegyalja 11.040/ −7.555/ 8.545/ 2.698/ −7.424/ 21.349/ Categorisation of CompI The CompI was analysed with respect to three relevant classes of the HI over Europe, namely: 900≤HI<1,500 °C; 1,500≤HI<2,100 °C; 2,100≤HI<3,000 °C, as explained in “Materials and methods”. Hence, the CompI was split into Mean Median Minimum Maximum NIQR TR 49.155 47.368 45.012 49.765 42.493 49.988 41.570 48.660 49.936 41.609 0.98 0.99 0.96 0.95 0.96 0.96 0.94 0.93 0.94 0.94 1.00 1.00 0.97 0.97 1.00 1.00 1.00 0.97 0.97 1.00 0.93 0.90 0.90 0.87 0.78 0.77 0.73 0.70 0.63 0.55 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.03 0.02 0.10 0.08 0.05 0.03 0.07 0.09 0.05 0.05 0.07 0.10 0.10 0.13 0.22 0.23 0.27 0.30 0.37 0.45 43.640 41.170 41.570 39.653 38.797 48.187 0.90 0.92 0.86 0.82 0.55 0.71 0.97 1.00 0.93 0.90 0.57 0.87 0.52 0.47 0.47 0.30 0.17 0.00 1.00 1.00 1.00 1.00 0.93 0.97 0.12 0.05 0.15 0.2 0.41 0.13 0.48 0.53 0.53 0.70 0.76 0.97 Int J Biometeorol Fig. 4 Left panels Differences in the mean patterns (2041–2070 minus 1961–2000), right panels NIQR (third quartile minus first quartile divided by the mean at each grid point) showing variability in the 16-member ensemble. Differences not statistically significant (NS) at the 99 % confidence level are shaded grey. a HI, b DI, c HyI, d CompI Int J Biometeorol three non-overlapping meaningful categories for viticultural zoning in Europe. Each year at a given location is thus keyed to one of these categories. The leading category at each location and for each selected time period is then detected and plotted. Only grid cells with at least 50 % of optimal years according to the total CompI (values equal to or higher then 0.5) were categorized. For the baseline period (Fig. 5a), this pattern clearly highlights that approximately all potential winemaking regions north of the 45°N parallel are keyed to the first category (associated with the HI first class, Fig. 5b). At lower latitudes, the most important exception is verified over the northern Iberian Peninsula, where large areas are also keyed to the first category; other minor exceptions occur over high altitude regions in southern Europe. The second and third categories are widespread over southern Europe (nearer the Equator than 45°N), with low altitude (warmer) areas in the Mediterranean Basin depicting a preponderance of the third category, such as in southwestern Iberia, northern Italy (Po valley) and many coastal areas. For both future periods (Fig. 5b, c) there is strong evidence for new regions suitable for viticulture in different parts of northern Europe (e.g. southern British Isles, the Netherlands, Denmark, northern Germany and Poland). In fact, the projected changes in the number of suitable grid boxes (CompI greater than 0.5) for 2041–2070 shows and increase poleward of the 50°N parallel (Fig. 6), though it gradually weakens towards 60°N (upper latitude limit in the present study). Conversely, many regions in southern Europe (nearer the Equator than 41°N), such as southern Iberia, shift to unsuitable conditions, which can be explained largely by the lack of precipitation and dryness (Fig. 2b). Within the latitude belt of 41–50°N there is no remarkable change in the number of suitable grid boxes, though there are some very significant shifts amongst the three categories. On the whole, new suitable regions northwards of 50°N are keyed mainly, as expected, to the first category (Figs. 5, 6). Further, most regions from 46°N up to 50°N tend to change from the first to the second category, while many regions within 39–46°N are projected to change from the first or second category to the third category. Therefore, the first category (the least heat demanding) is projected to be located essentially northwards of 50°N, as no new regions of this category are expected to arise at lower latitudes. The second and third categories undergo a northward displacement, leaving many current winemaking regions in southern Europe with unsuitable conditions, primarily because of the severe dryness that is expected to prevail in their future climates. Inter-annual variability Due to the relevance of the inter-annual variability in viticultural zoning, corresponding climate change projections are also analysed. As stated above, apart from a few exceptions, the selected bioclimatic indices are normally distributed and their inter-annual variability can thus be assessed by their sample standard-deviation. The map of the ratios between the ensemble mean inter-annual standarddeviations of the HI for 2041–2070 and 1961–2000 reveals values significantly above one (higher variability) over large areas of Europe, particularly over central Europe, the British Isles and over some mountainous regions, such as the Alps (Fig. 7a). These results also depict low model uncertainties, with the exceptions of some regions of Iberia and some regions of central and northeastern Europe (Fig. 7b). The DI inter-annual variability (Fig. 7c) also shows an upward trend, especially in central and eastern European regions, with larger values over Great Britain. The projected increases in precipitation over these regions, combined with increased interannual variability, may become harmful to viticulture, with enhanced risks of pests and diseases. These results also reveal low model uncertainty (Fig. 7d). In addition to the increase in the inter-annual variability of the HI and DI, the HyI shows significant increases in its inter-annual variability over northeastern Europe (not shown). As such, there is evidence for an overall increase in the inter-annual variability under future climates, which may also comprise an increase in the occurrence of extremes, although this analysis is left to a forthcoming study. Summary and discussion The projected and well-documented warming over Europe (cf. Christensen et al. 2007) leads to changes in the thermal indices (GSS and HI; Fig. 2a), with significant increases, particularly over southern and western Europe (over 400 °C increase in HI for 2041–2070). Further, dryness conditions in the growing season (GSP and DI; Fig. 2b) are projected to undergo an enhancement over southern Europe, while humidity levels (GSP and HyI; Fig. 2c) are expected to remain relatively high over central and northern Europe. All these changes are also corroborated by the CompI, not only by its aggregate values (Fig. 2d), but also in relation to the different classes of the HI considered for category analysis (Figs. 5, 6). These projections are consistent with other recent studies by Neumann and Matzarakis (2011), for Germany, and by Duchene and Schneider (2005), for Alsace, France. Analogous changes in the mean patterns of HI (Fig. 2a) have already been reported, including an increase of about 300 units for six winegrowing European regions over the last 30–50 years (Jones et al. 2005a). Additionally, under a future warmer climate, higher temperatures (above 30 °C) may often inhibit the formation of anthocyanin (Buttrose et al. 1971) and thus reduce grape colour (Downey et al. 2006). All these changes may imply the selection of new winegrape varieties and a reshaping of the European viticulture. Int J Biometeorol Fig. 5 Leading categories in the CompI (HI classes 1, 2 and 3) for the baseline period (a) and the two future periods (b, c) Analysis of the GSP and DI provides evidence of very dry climates over southern Europe (Fig. 2b). Although grape quality is generally favoured by moderate water stress conditions during berry ripening (Koundouras et al. 1999; Int J Biometeorol Fig. 6 Latitudinal differences (2041–2070 minus 1961–2000) in the number of grid cells equal to or above 0.50 in the CompI Santos et al. 2003), severe dryness (DI below −100 mm) in many Mediterranean-like climate regions may be damaging (Chaves et al. 2010); some of these regions are actually projected to have a GSP below 200 mm (southern Iberia, southern Italy, Turkey and Greece). Changes in winemaking practices are thereby expected to arise in these regions, including crop irrigation or water stress mitigation methods (Flexas et al. 2010). In the wetter regions in central and Fig. 7 a, c Ratio between the averages of the 16 inter-annual standarddeviations (calculated for each of the 16 ensemble members separately) in 2041–2070 and 1961–2000 of the HI (a), and DI (c). b, d NIQR northern Europe, however, pests and diseases can also be a drawback to wine production, since changing climate conditions may modify the complex interrelationships between vine, pest and disease development (Stock et al. 2005). Regarding downy mildew, patterns of change in the HyI suggest, at first sight, low risks of contamination in southern Europe, but moderate-to-high risk at higher latitudes, the latter as a result of warm and wet conditions. Nonetheless, implications of a future increase in the HyI at the continental scale may not be too dramatic, mainly because, in the emerging winemaking areas, where thermal conditions will gradually become favourable to wine production, the HyI will remain below the maximum threshold of 7,500 °Cmm in most years. Further, a projected strengthening of the inter-annual variability in the HI and DI may result in additional constraints for this perennial crop and for the winemaking sector as a whole, particularly in view of an increasing irregularity and unpredictability of yields and wine quality. A reshaping of the European regions suitable for grapevine growing is likely to occur, taking into account the projections of CompI. Many regions throughout Europe are shown to be undergoing a change to a higher CompI category. As an illustration, some regions in France and showing variability in the 16-member ensemble for the ratios of the HI (b) and DI (d). Non statistically significant ratios (NS) are shaded grey Int J Biometeorol Germany will in the future present similar values to those seen today in the Mediterranean Basin. A general decrease in the number of suitable regions below 39°N might also be expected. This outcome is also supported by previous findings (e.g. Kenny and Harrison 1992; Jones et al. 2005b; Stock et al. 2005; Fraga et al. 2012). Overall, shifts in CompI classifications throughout Europe suggest modifications in the suitability of a given region to a specific winegrape variety and are expected to influence wine yield/ quality attributes. The assessment of the uncertainty associated with the climate change projections is of great importance for informing decision-makers. Following the recommendations in Christensen et al. (2010) and Weigel et al. (2010) in our study, model uncertainty for viticultural zoning was assessed by considering all members of the ensembles with equal weight. Although the ensemble means shown in the current study are in overall agreement with a previous study that employed a single model for similar purposes (Malheiro et al. 2010), thus generally corroborating previous findings, future climate conditions can depend greatly on the model experiment at local/ regional scales (Dessai and Hulme 2007). In fact, at these scales, remarkable differences were found between singlemodel projections and the ensemble projections presented here, which plainly substantiate the current study. The increase in CO2 concentration is expected to be beneficial for winegrape growth (Moutinho-Pereira et al. 2004; Goncalves et al. 2009; Bindi et al. 1996). Reflecting the settings of the ENSEMBLES project (van der Linden and Mitchell 2009) in this study we considered only the A1B emission pathway. A more pronounced increase in atmospheric CO2 concentration is predicted by the A2 emission scenarios, especially relevant to the second half of the century, with implications that need to be examined in future studies. The impacts of the aforementioned changes in climate suitability for the winemaking sector in Europe, can be summarized as follows: (1) some southern regions (e.g. Portugal, Spain and Italy) may face detrimental impacts owing to both severe dryness and unsuitably high temperatures; (2) regions in western and central Europe (e.g. southern Britain, northern France and Germany), some of which are world-renowned winemaking regions, might benefit from future climate conditions (higher suitability for grapevine growth and higher wine quality); and (3) new potential winegrape growth areas are expected to arise over northern and central Europe, where conditions are currently either marginally suitable or too cold for this crop. It is still worth mentioning that the higher inter-annual variability (climate irregularity) in the future over most of Europe may lead to additional threats to this sector. Furthermore, the shortening of the growing season resulting in earlier phenological events, reported by several studies (Webb et al. 2012; Bock et al. 2011; Daux et al. 2011; Chuine et al. 2004), may indicate the need to adapt the time periods and classes in which the bioclimatic indices are commonly calculated. Since grapevine phenology and wine quality were shown to be correlated with HI (Jones et al. 2005a; Orlandini et al. 2005), this limitation can, to some extent, be overcome by adding new classes to the existing classical bioclimatic indices, instead of modifying the time periods (difficult to achieve due to the extent of the regions studied). A similar approach was indeed carried out by Santos et al. (2012b) using a new low-limit class for the HI (900–1,200 °C). Future changes in the viticultural zoning in Europe impose new challenges for the winemaking sector. These modifications give clues to the development of appropriate strategies to be taken by the winemaking sector to face climate change impacts. There have already been reports of acclaimed winemaking regions that may become unsuitable for premium wine production within the current century (Hall and Jones 2009). As the patterns discussed in this study are available at a relatively high spatial resolution (25–30 km), regional climate change assessments are permitted, enabling the development of local adaptation and mitigation measures, drawn specifically for the winemaking sector. Changes in soil and crop managements, as well as genetic breeding and oenological practices, are crucial for a better adjustment between viticulture and future environment. These measures need to be planned adequately and timely by stakeholders, policymakers, and by the different socioeconomic sectors that are directly or indirectly influenced by the vineyard and winemaking activities. Acknowledgements We acknowledge the ENSEMBLES project (contract GOCE-CT-2003-505539), supported by the European Commission’s 6th Framework Programme (EU FP6) for supplying the model datasets (http://ensembles-eu.metoffice.com/). We thank Dr. Joaquim Pinto, at the University of Cologne, the German Federal Environment Agency and the COSMO-CLM consortium for providing COSMO-CLM data. We also acknowledge E-OBS and the data providers in the ECA&D project (http://eca.knmi.nl). This study was carried out under the Project Short-term climate change mitigation strategies for Mediterranean vineyards (Fundação para a Ciência e Tecnologia - FCT, contract PTDC/AGR-ALI/110877/2009). 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