Technical Yearbook 2023

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 and other authors (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 and other authors (2022).

(SPEI) shows that drought conditions are likely to be far more common in the future across all the zones (Jack and other authors, 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

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TECHNICAL YEARBOOK 2023