Handbook for Irrigation of Wine Grapes in South Africa

Chapter 1

Climate

1.1 INTRODUCTION Since elements such as incoming solar radiation and air temperature can affect wine quality or style in a positive way, the climate of a region is important in wine production. On the other hand, high levels of humidity can increase the occurrence of diseases and pests, whereas strong winds may cause physical damage to grapevines. Given that vineyards for wine production are primarily planted in a Mediterranean climate with hot, dry summers and limited rainfall (Table 1.1), their water requirements must be replenished by irrigation. For example, vineyards in the Breede River and Lower Olifants River regions depend totally on irrigation. In most cases, irrigation water is obtained from winter rainfall stored in on-farm dams, or large dams which feed irrigation schemes. Where possible, irrigation water is pumped from rivers or bore holes. TABLE 1.1. Long term mean annual rainfall in grape growing regions. Data supplied by the ARC Institute for Soil, Climate and Water in Pretoria.

Rainfall (mm)

Region

District

Autumn & winter Spring & summer Total

Coastal

Grabouw

645

366

1 011

Stellenbosch

490

254

744

Piketberg

580

263

843

Breede River

Tulbagh

392

182

574

Robertson

164

116

280

Little Karoo

Montagu

176

149

325

Barrydale

204

154

358

Lower Olifants River

Lutzville

93

47

140

Lower Orange River

Upington

56

183

239

It is only in some areas of the Coastal region where grapevines can be grown without irrigation, i.e. if they have deep, well-developed root systems. These dryland, or rainfed, vineyards survive on the winter rainfall stored in the root zone and rainfall in spring. Based on the foregoing, it is clear that winter rainfall is by far the most important climatic variable with regard to sustainable viticulture. The

14 CHAPTER 1 – CLIMATE