WINETECH Technical Yearbook 2020

Seasonal weather variation within local mesoclimates explained using high resolution climate data (PART 3)

in the varieties planted in wine regions worldwide. Driving potential shifts in suitable zones for viticulture with some regions becoming too warm all together, while others become more viable. The selection and application of climatic indices need to be reviewed in the context of climate change, especially the classification classes that are internationally used to describe the indices. South Africa is warm to intermediate, with many areas classified as too hot. There are, however, many environmental factors moderating the daily temperatures, as well as irrigation supporting viable growth and production in hot areas, making these areas cooler and viable for high quality table wines. Factors such as aspect, altitude, site exposure and distance from the sea or large water bodies generate various mesoclimates and unique environments for viticulture. Due to the complexity of factors influencing the environment and the sensitivity of the grapevine to change, the site and seasonal variability should be explained using higher resolution information. Bioclimatic indices are effective in highlighting general

site and seasonal differences, and for global comparisons. The classification classes set for the climatic indices are also too large, making it difficult to see smaller changes. Finer scale analysis, using hourly data as frequency analysis (how many hours at a specific temperature range) and for diurnal analysis (the tempo of daily change) of sites and seasons is important, within the climatic indices describing a site or season. Hourly information highlights the diurnal trend of warming, speed of warming and diurnal cooling for temperature, relative humidity and wind. Figure 1 describes the study sites ranging from a cooler site, to intermediate sites and a warmer site. Environmental conditions quantified using traditional bioclimatic indices, additional variables and hourly resolution data. The hourly data analysis did not consider pre-set cut-offs in the weather data, as seen in other climatic studies, but rather analysed the entire temperature, wind and relative humidity profiles, allowing the data to “express itself” (classes used can be seen in table 1).

JUNE 2020

TARA SOUTHEY: Centre for Geographical Analysis, Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch KEYWORDS: Climate, terrain, seasonal, hourly, adaptation

Increased seasonal variation has become a reality in the context of climate change. Should we be reconsidering howwe measure a season? This article highlights findings from an extensive study, considering climate change impacts on viticulture over four growing seasons. Increased seasonal variation in weather is a growing reality and concern in the context of climate change. The last few seasons, the agricultural sector has faced extreme seasonal events, not always quantifiable using traditional climate indices (heat summations over the growing season). As climate exerts a dominant

influence on wine production, driving baseline suitability, largely controlling crop production and quality and ultimately driving economic sustainability of wine producing enterprises. Small changes in climate have the potential to bring about significant changes in the management of existing vineyards, as well as changes

TABLE 1. Frequency analysis threshold classes for temperature, relative humidity, wind speed over the climate band, separated into different levels. Element Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level 7 Level 8 Level 9 Level 10 T (°C) 0

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