Technical Yearbook 2023

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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 and other authors (2016).

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TABLE 1. Geographic and climatic characteristics of the six study sites in the Western Cape, South Africa (extracted from TerraClim products, and Jack and other authors, 2022). Variables and climate change 1. Lutzville 2. Skurfberg 3. Koue Bokkeveld 4. Roundstone 5. Polkadraai 6. Hemel and Aarde Agro-climatic zone Hardeveld Sandveld North Cederberg Bokkeveld Swartland Cape Town – Winelands Rûens-West Slope (%) 1,4 2,5 9,6 10,8 5,8 10,4 Solar radiation 1404321 1485178 1532318 1396896 1384975 1412797 Elevation (m) 12 540 1 036 327 221 266 Distance to coast (km) 15,2 34,3 104,3 49,5 13,7 4,3 Mean wind speed (m/s) 4,5 5,7 4,5 5,8 5,2 6,4 Growing degree days 1 942 1 935 1 505 2 083 1 771 1 619 Growing season temperature 19,2 19,2 17,1 19,8 18,4 17,7 Aspect East East West West South South Mean soil depth (cm) 612 668 333 807 896 351 Mean clay (%) 2 3 12 17 20 10 Rainfall (annual) 57 266 780 366 544 507 Rainfall (summer) 1 11 35 24 41 65 Rainfall (winter) 46 121 296 179 270 207

Strong night time warming. Strong drying and less heavy rainfall. Strong drying. Strong warming. Drought.

All-year strong warming. Strong drying and less heavy rainfall. Strong drying. Strong warming. Very hot days. Drought.

All-year strong warming. Strong drying and less heavy rainfall. Strong drying. Strong warming. Very hot days. Drought.

All-year strong warming. Strong drying and less heavy rainfall. Strong drying. Strong warming. Drought.

Strong daytime warming. Strong drying and less heavy rainfall.

Autumn/spring warming. Drying. More all-year rainfall.

Climate trend

Strong drying. Warming. Drought.

Drying. Warming.

Climate future

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 and other authors, 2021). Analysis of the standardised precipitation evaporation index

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TECHNICAL YEARBOOK 2023