Handbook for Irrigation of Wine Grapes in South Africa

Chapter 1

dependency of rainfed grapevines on rainfall in the Coastal region is illustrated by the positive yield response to rainfall, particularly the cumulative rainfall in July and August (Fig. 1.1). Furthermore, the regression equation indicates that the yield will be almost zero if no rain occurs in July and August under the given conditions.

Figure 1.1

12

2014

10

8

2015

2017

6

2016

4

Yield (t/ha)

2018

2

y = 0.0625x – 0.0519 R² = 0.9925

0

0 20 40 60 80 100 120 140 160 180

Rainfall (mm)

FIGURE 1.1. The effect of rainfall during July and August on the yield of dryland Cabernet Sauvignon near Philadelphia in the Coastal region. The dashed vertical line indicates the 71-year mean rainfall.

1.2 CLIMATE CLASSIFICATION In South Africa, wine grapes are grown in two broad climatic regions. Most of the wine grape vineyards occur in the Western Cape which has a Mediterranean climate. Wine grapes are also grown under summer rainfall conditions in the Northern Cape and on a limited scale in the other provinces. However, if a more accurate climate classification is used, there are distinct climatic differences within the two broader climate regions. The internationally accepted Köppen-Geiger classification separates climates into five primary groups based on latitude, i.e. tropical, arid, temperate, cold and polar (Peel et al. , 2007). In South Africa, wine grapes are only grown under arid and temperate conditions (Table 1.2). Each of the primary groups are further divided into secondary and tertiary groups based on air temperature and precipitation relationships. Furthermore, the Köppen- Geiger classification uses a so-called precipitation threshold, which is calculated according to the annual rainfall distribution as described in Table 1.2. The climate types for South Africa are indicated in Figure 1.2, but it should be noted that limited climate variation may occur within the demarcated areas.

IRRIGATION OF WINE GRAPES 15