Vulnerabilities

Northward shift optimal climate zones Portuguese grapevine varieties

Climate change is expected to change the optimal zones for grape varieties. Grapes are expected to ripen earlier in warmer climates (5,20), but unbalanced ripening may lead to lower wine quality (6). Knowledge about how the spatial distribution of the optimal climatic zones for grapevine varieties may change under global warming helps the sector to adapt to future climates. It is to be expected that current growing regions of varieties reflect their optimal climatic zones since growers have been selecting the varieties that best suit the regional climatic conditions (7,17). We can characterize climatic conditions at the zones of different varieties and see how locations with these conditions shift under future projections of climate change. This was done for 44 grapevine varieties in Portugal (4,17).

Climatic conditions were characterized by the so-called growing degree days (GDD) (8), or growing degree hours (GDH) in combination with chilling portions (CP) (17). These indices correlates well with grapevine development, growth and yield, and with wine quality. GDD is the sum of the daily averaged temperatures above the base temperature of 10 °C for all days in the growing season (April-October) (8). DGH is the thermal accumulation on an hourly timescale, using two cosine functions between a base temperature (4 °C) and an upper limit temperature (36 °C), with an intermediate optimum at 26 °C; CP is a measure of the chill conditions during the wintertime dormancy period (17). A minimum chilling accumulation in the winter is required to break dormancy and trigger a regular budburst phase. Chilling requirements are widely fulfilled in current climatic conditions in Portugal and it is thereby not a major limitation of present-day Portuguese viticulture (17).

For the GDD method, future optimal zones for Portuguese varieties in Europe have been assessed for the period 2041-2060, compared with 1950 – 2000, under a scenario of moderate and strong climate change (the so-called RCP4.5 and RCP8.5 scenarios), based on a large number of global climate models. The future optimal zones are to the north of current zones for all grapevine varieties: both climate change scenarios project an extension of these optimal zones throughout Europe, up to France, Germany, Hungary, Croatia, Serbia, Romania, Poland and Ukraine, depending on the variety (4). The northward shift may indicate that some regions in Portugal, especially the south, will no longer provide optimal climatic conditions for most current varieties. However, this may also provide an opportunity to select other international varieties, with higher thermal demands (4).

For the GDH/CP method, future optimal zones for Portuguese varieties in Europe have been assessed for the period 2041-2070, compared with 1981-2005, also under the aforementioned scenarios of moderate and strong climate change (RCP4.5 and RCP8.5 scenarios), based on a number of global climate models (17). Similar to (4), the results show a northward (or rather: northeast) shift of optimal zones for current varieties, whereas some regions in the south will no longer provide optimal climatic conditions for most current varieties (17). In addition, the study shows that chilling requirements might not be totally achieved in warmer future climates, particularly in southern Portugal, thus bringing new challenges to Portuguese viticulture (17).

Projections for the future periods of 2041 - 2070 and 2071 - 2100, compared with the baseline period 1981 - 2015, for a moderate (RCP 4.5) and high-end (RCP 8.5) scenario of climate change show increases in the growing-season mean temperatures in all Portuguese winemaking regions. These increases are accompanied by increasing severe dryness, mainly in south-eastern Portugal and along the upper Douro Valley in north-eastern Portugal (19).

Douro Valley

The ‘Douro wines’ are quality wines, produced from grapes grown along the Douro Valley, in the old province of Trás-os-Montes e Alto Douro, Portugal (1). A qualitative assessment of the effect of future climate change on Douro wine production was undertaken using information from climate change simulations (IPCC scenarios A2 and B2) from the PRUDENCE (2) project for 2071–2100 compared with 1961–1990. These climate scenarios are expected to favour an increase in wine production along the Douro Valley because of the combined effects of temperature and precipitation in late spring and early summer (1).

According to these climate scenarios, projected values of wine production in the Douro region for 2071–2100 indicate an increase in both the mean and standard deviation, respectively, of 6% and 4% for the B2 scenario, and of 24% and 35% for the A2 scenario, relative to the control run (1961–1990). However, given the spatial differences in climate and production in different regions of the Douro Valley, one would not expect future production to change the same in all areas. For instance, further decreases in rainfall will make it extremely difficult to continue to produce at all in the most eastern area (Douro Superior), while the most western areas (Baixo Corgo and Cima Corgo) might respond more slowly to these changes (1).

From a multi-model ensemble of Global and Regional Climate Models following the A1B scenario possible changes in the wine production in the Douro Valley for future decades have been estimated. Wine production is projected to increase by about 10% by the end of the 21st century, while the occurrence of high production years is expected to increase from 25% to over 60%. In particular, the rising heat stress and/or changes in ripening conditions could limit the projected production increase in future decades, however (3).

The estimated increase in wine production is attributable to the increase of the mean difference between the maximum temperature in July and the minimum temperature in May from 22.4°C in the control run to 23.5 (24.9)°C in B2 (A2) and to the decrease in precipitation in May and June from 73.0 mm in the control run to 64.5 (60.7) mm in B2 (A2). Results showed that high winter rainfall (in March) has a positive impact during the growing stage, whereas higher temperatures during late spring are beneficial for the flowering and véraison stages (1).

Under a high-end scenario of climate change (the so-called RCP 8.5 scenario), the shift to warmer and drier conditions in the second half of this century may be outside the range for quality wine production (18).

Adaptation strategies

One way to adapt to climate change is to select grapevine varieties that best fit projected future climate conditions in a certain area (4). There are many other measures growers can adopt to mitigate the negative impacts of climate change. As short-term measures, they can adjust pruning times and training systems (9), apply leaf sunscreens (e.g. Kaolin, Bordeaux mixture) or vine shadings (10), implement controlled/deficit irrigation (11), cover cropping and tillage treatments (12). Numerous approaches could be used for long-term adaptations including improvements in rootstock and clonal selection (13), relocations to cooler areas (14), increasing soil depths and water holding capacities (15), and genetic breeding of new varieties (16). When there is need of irrigation, precise strategies such as deficit irrigation should be considered. It is also possible to relocate the vineyards in the long term to cooler sites such as higher elevations or areas with lower solar exposures or closer to the sea. These relocations should also be carefully planned in order to maintain as much as possible freshwater resources and natural habitats (18). 

Irrigation or the introduction of new varieties are likely adaptation measures to maintain the viability and sustainability of regional viticulture in Portuguese winemaking regions that will be subject to increasing severe dryness in future decades (19).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Portugal.

1. Gouveia et al. (2011)
2. Christensen and Christensen (2007), in: Gouveia et al. (2011)
3. Santos et al. (2013)
4. Fraga et al. (2016)
5. Chuine et al. (2004); Jones et al. (2005a); Bock et al. (2011); Webb et al. (2012), all in: Fraga et al. (2016)
6. Webb et al. (2011); Hannah et al. (2013); Fraga et al. (2014c), all in: Fraga et al. (2016)
7. Van Leeuwen et al. (2008), in: Fraga et al. (2016)
8. Chuine et al. (2003); Jones (2003); Sadras and Moran (2013); Neumann and Matzarakis (2014), all in: Fraga et al. (2016)
9. Duchene and Schneider (2005), in: Fraga et al. (2016)
10. Greer et al. (2011), in: Fraga et al. (2016)
11. Flexas et al. (2010), in: Fraga et al. (2016)
12. Monteiro and Lopes (2007), in: Fraga et al. (2016)
13. Koundouras et al. (2008), in: Fraga et al. (2016)
14. Fraga et al. (2014b), in: Fraga et al. (2016)
15. Pellegrino et al. (2004), in: Fraga et al. (2016)
16. Duchene et al. (2012), in: Fraga et al. (2016)
17. Santos et al. (2018)
18. Blanco-Ward, D. et al. (2019)
19. Santos et al. (2020)
20. Rodrigues et al. (2022)