WINETECH Technical Yearbook 2020

traditional bioclimatic indices and daily descriptions of sites compared to hourly profile analysis. The study used six sites with different climatic classifications as described by traditional bioclimatic indices for the period 2012 to 2016. The seasonal climate profile was described based on hours within specific classes with no set cut-offs for temperature, relative humidity and wind specifically. This has provided better insights to guide adaptive strategies, as understanding how the climate is driving the grapevine responses. This analysis gives insights into the temperature ranges and the duration of hours at specific thresholds that could impact the grapevines optimal physiological functioning. Understanding the climatic kinetics/dynamics at field level, aids more effective adaptive strategies.

Globally, the varietal spectrum would change substantially in future since the suitability for the cultivation of a given cultivar is largely temperature driven. Frequency analysis would greatly and effectively guide decision making in this regard. Using the climate profile based on hours within specific classes with no set cut- offs, isolating when in each season there are shifts that would influence grapevine. This detail of seasonal profiling can be used to optimise distribution of a grapevine cultivar in a specific environment, based on grapevine physiology thresholds for optimal functioning in the context of climate change. SUMMARY The Western Cape wine grape terroir climate variability is dictated by latitude, water sources, topography and climate change. Traditional bioclimatic indices use cumulative units potentially masking some specific events/conditions within seasons. With climate change, seasonal variability and extreme events are increasing. The traditional bioclimatic indices do not account for environmental conditions at plant level, information needed for effective adaption strategies. Frequency analysis based on high resolution (hourly) weather data can detect the extremities and duration of conditions at a specific locality. This article explores the possible climatic details overlooked in the use of

FIGURE 6. Heat map: November 2018 to March 2019: Hours experienced >35°C. More hours above 35°C, red areas have more hours at warmer conditions, less favourable for optimal photosynthesis, more orange to red areas would require management practices to help with the heat.

cut-off thresholds, is a novel approach that explains the grapevine responses. Mapping the frequency of hours at specific thresholds, provides additional information for management at field level. Figure 2, 3 and 4 show the mapping application of hours at specific physiological thresholds important for grapevine functioning. The maps highlight the areas with more or

less hours at specific thresholds <20°C (Figure 4), between 25-35°C (figure 5) and greater than 30°C (figure 6), tem­ perature important for grapevine photo­ synthesis. This information in a spatial format adds additional information to aid decision-making over time and space (www.terraclim.co.za).

For more information, contact Tara Southey at tara@sun.ac.za.

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