Handbook for Irrigation of Wine Grapes in South Africa

Chapter 1

1.3.4 COOL NIGHT INDEX The CI ′ is based on the minimum mean night temperatures during the month preceding harvest (Bruwer, 2010 and references therein). The objective of the CI ′ is to assess the qualitative potential of a wine region with respect to wine colour and aroma. The CI ′ is based on the minimum daily temperature during March (Table 1.7). An example where the CI ′ in the Lower Olifants River region was analysed by Bruwer (2010) is presented in Figure 1.6. Unlike the GDD and HI, only two regions could be demarcated according to the CI ′ . This suggests that the CI ′ might not be sensitive enough for viticultural purposes in South Africa. TABLE 1.7. The CI ′ used to classify the climate with respect to potential for viticulture based on night temperature in the month preceding harvest (Tonietto & Cabonneau, 2004 and references therein). Viticultural climatic class Class code Class interval (ºC) Warm nights CI ′ -2 > 18 Temperate nights CI ′ -1 > 14 < 18 Cool nights CI ′ +1 > 12 < 14 Very cool nights CI ′ +2 < 12 2 200 2 400 2 600 2 800 3 000 3 200 3 400 3 600 3 800 HI (ºC) Class HI +3 Class HI +2 Class HI +1 Ebenaeser Lutzville Vredendal Klawer R 2 = 0.9984 Figure 1.5

0

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Distance (km)

Figure 1.6

17

Klawer

16

15

Class CI h -1

14

Lutzville

(ºCI h C)

Class CI h +1

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Vredendal

Ebenaeser

12

Class CI h +2

11

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Distance (km)

FIGURE 1.6. Effect of distance to the Atlantic Ocean on viticultural potential in the Lower Olifants River region according to the CI ′ (Bruwer, 2010).

IRRIGATION OF WINE GRAPES 23