This article is based on a joint presentation by the three authors at the 2nd Chenin Blanc International Congress in Stellenbosch, 1 – 3 November 2022.
New ways and new sites to plant Chenin blanc in years to come in the quest to deal with climate change.
Background
The supreme adaptability of Chenin blanc to diverse regions makes it a very interesting case study for exploring the future of wine under a changing climate. Production regions in both France and South Africa are already undergoing climatic shifts linked to warming and changing rainfall patterns. In the Western Cape Province of South Africa, Chenin blanc is successfully produced in widely ranging climates. With climate change, the shifting mosaics of micro-climates will play an important role in vineyard decision-making for the future.
Approach and case study sites
This study was structured around three components:
- The latest climate change science – recent trends and modelled future projections – for the Western Cape (for details of methods and results, see Jack et al., 2022);
- The finer-scaled web-based spatial tools provided by TerraClim that can aid climate-adaptive decision making at farm and vineyard level (terraclim.co.za); and
- Practical experience in vineyard planning and management for long-term vine resilience and climate adaptability (oldvineproject.co.za).
We chose six Chenin blanc vineyards in the Western Cape as case studies, spanning the range of distribution from north to south along strong climatic gradients (Figure 1, Table 1).
FIGURE 1. Historical mean daily maximum temperature in February (left) and mean annual rainfall (right) for the various agro-climatic zones of the Chenin blanc production regions of South Africa. The site numbers correspond to the case study sites described in Table 1. Source: Jack et al. (2016).
Climate change trends and future projections
Trends in daily minimum temperature (1902 – 2020) show strong increases in autumn and spring along the West Coast, but moderate warming for the two southernmost sites, and across the whole region in summer and winter (Figure 2). Increasing trends in daily maximum temperature are greatest during autumn and spring, especially in the interior, higher-lying areas (Figure 2). Daytime warming has been more muted in summer and winter. Trends in seasonal mean annual rainfall (1982 – 2020) indicate significant drying during autumn across all the sites (Figure 3). Trends in core winter (June – August) rainfall are mixed and demonstrate a dipole from the northwest towards the southeast, from drying to apparent wetting. Potential evapotranspiration (PET) has consistently increased across all sites in all seasons, although more strongly in spring and summer, and on the southwestern and southern coastal plains.
FIGURE 2. Mean seasonal daily minimum (top) and maximum (bottom) temperature trends (°C/decade) for the period 1902 – 2020. The maps on the left are for summer (DJF = December, January and February) and the maps on the right are for autumn (March, April and May). Black circles indicate areas of strong warming trends. Source: Jack et al. (2022).
FIGURE 3. Mean seasonal total rainfall trends (mm/decade) for the period 1982 – 2020. MAM = March – May; JJA = June – August; SON = September – November; DJF = December – February. Diagonal hashing indicates trends that are not statistically significant. Black circles indicate areas of clear drying trends. Source: Jack et al. (2022).
Future-modelled climate projections (to the mid-century) suggest a further drying associated with hemispheric climatic processes, including a poleward displacement of the westerly wind belts and storm tracks during the winter rainfall period. Projected changes in annual total rainfall show drying of up to 40 – 80 mm per year, or up to around 30% in some production regions, but for most regions, the drying is projected to be between 5 and 15% (Figure 4). Some models indicate slight wetting of less than 25 mm per year (less than 10%) in the western Overberg/Agulhas region.
Projected changes in annual mean temperature show a range of possible increases from lower (around 1.2°C) to higher magnitude (around 2.4°C). A lower rate of warming is projected for the southern coast, linked to the moderating influence of the two oceans, and warming will likely be stronger in the interior regions (Figure 4). The diurnal temperature range could increase or decrease, depending on location. By the mid-century, the models project a significant decrease in areas suitable for chill-sensitive crops, particularly in the lower-lying and coastal areas (Figure 5, Midgley et al., 2021).
FIGURE 4. Projected future changes in annual total rainfall (mm) (left) and annual mean temperature (°C) (right) for the period 2030 – 2060 for four “archetype” climate models representing the range of model outcomes. Figure titles are the name of the model and the area average change in rainfall or temperature. Diagonal hashing indicates trends that are not statistically significant. Source: Jack et al. (2022).
FIGURE 5. Historical (left map) and projected future (right map, 2046 – 2065) accumulated seasonal positive chill units for the Western Cape Province. Source: Midgley et al. (2021).
Analysis of the standardised precipitation evaporation index (SPEI) shows that drought conditions are likely to be far more common in the future across all the zones (Jack et al., 2022). The increase in such conditions in the northern zone (Cederberg to Sandveld) is stronger, and the increase in the southern coastal zone (Rûens-West) is somewhat weaker than elsewhere.
Thus, climate change is playing out differently across the Chenin blanc production regions of South Africa. The key message is one of continued warming, increasing rainfall variability and general drying over the next two to three decades. The mountain and ocean influences will play a large role in local dynamics. Even when rainfall decreases are not projected, or do not manifest, increasing temperatures will almost certainly bring significant water balance challenges to grape production. We can expect shifts in current suitability for Chenin blanc, but also possibilities of new sites becoming suitable.
TerraClim
Temperature increases may shift plant phenology, ripening and harvest dates, potentially affecting quality, yield and economic sustainability. This emphasises the need for hourly weather data at the production unit level, as climate and terrain underpin most biological systems. The South African wine industry has long been concerned about climate change. In 2018, Winetech (the industry’s research funding agency, www.winetech.co.za) funded Dr Tara Southey to initiate the TerraClim research and development project, with the aim to improve our understanding of the potential impacts that this phenomenon may have. TerraClim is currently collecting data from more than 400 weather stations and 100 loggers throughout the Western Cape at hourly intervals. Plans are afoot to substantially increase the climate database and extend it to other regions in South Africa.
TerraClim has developed and implemented novel geostatistical and data science techniques to model climatic conditions at all farms within the TerraClim region, for multiple seasons, to contextualise the local environment in the context of increased seasonal climate variability. The resulting climate surfaces, integrated with terrain variables, are available via the web application www.terraclim.co.za, reports or private consultation. The climate surfaces are also being used as input to geospatial techniques to identify areas (e.g. vineyards) where conditions are most variable and (based on recent climate records) most suitable for particular cultivars and varieties. Refer to Table 1 for the site-specific data extraction per the Chenin blanc case study site. TerraClim solves the problem of data inaccessibility by providing highly-detailed, up-to-date, field-specific climate data at regional scales. This data is ideal for generating historic and current climatic and physical (terroir) profiles for each individual field, orchard or vineyard.
This is an extremely valuable tool that is currently being expanded to a range of crop types, cultivars, clones and rootstocks, to further enable adaptive strategies for climate resilience.
Practical approaches
Site selection can be matched with appropriate existing or innovative vineyard design, establishment and management methods to achieve a high level of resilience and sustainable yield, as well as a range of wine styles. The role of soil health will be increasingly important to assist the plant to become resilient against climatic stresses. Practical ways of designing to harvest and reuse all rainfall water and increase the levels of water tables can be considered. The rebuilding of ‘vleilande’ or wetlands can build a biodiverse system for all kinds of insects and small animals and also increase the levels of the water tables. Mulching could be used to preserve soil moisture, avoid the use of herbicides and build soil reserves. Certain varieties could benefit from a sprawl or bush vine training system, rather than the VSP (vertical shoot position) system. There are many ways in which the threat of climatic stresses, which could cause lower acidities and higher pH in grapes, flooding, sunburn, shrivelling of berries, etcetera could be tackled.
Significance to industry
The versatility of Chenin blanc, together with careful site selection, appropriate vineyard design and best viticultural practices, will allow this wonderful variety to survive and flourish well into the future, even with climate change. However, the choices made now are critical to securing a sustainable future for Chenin blanc in South Africa and other producing countries.
Abstract
The Chenin blanc wine grape cultivar is adapted to a wide range of climates and soils. Climate change in the Western Cape, South Africa, is causing warmer and dryer conditions. This will impact production and berry quality, but there are many practical ways in which this threat could be tackled. A science- and data-driven approach, using available tools and analysis at multiple scales, can be matched with appropriate vineyard-level planning and practices to build resilience and ensure sustainability.
References
Jack, C., 2016. Climate change in the Western Cape. In: Midgley, S.J.E., New, M., Methner, N., Cole, M., Cullis, J., Drimie, S., Dzama, K., Guillot, B., Harper, J., Jack, C., Johnston, P., Knowles, T., Louw, D., Mapiye, C., Oosthuizen, H., Smit, J. & Van den Broeck, D. (2016). A status quo review of climate change and the agriculture sector of the Western Cape province, Chapter 4, pp. 64 – 100. Report submitted to the Western Cape Department of Agriculture and the Western Cape Department of Environmental Affairs & Development Planning. African Climate & Development Initiative, University of Cape Town, Cape Town.
Jack, C., Van Aardenne, L., Wolski, P., Pinto, I., Quagraine, K. & Kloppers, P., 2022. SmartAgri: Updated climate change trends and projections for the Western Cape. Report submitted to the Western Cape Department of Agriculture. Climate System Analysis Group, University of Cape Town, Cape Town.
Midgley, S.J.E., Davis, N. & Schulze, R.E., 2021. Scientific and practical guide to climate change and pome/stone fruit production in South Africa (Part 1): Atlas of key climate-related variables for historical and future climate conditions as relevant to pome and stone fruit production. Report submitted to Hortgro Pome and Hortgro Stone, Stellenbosch, South Africa.
For more information, contact Stephanie Midgley at stephanie.midgley@westerncape.gov.za.
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