Handbook for Irrigation of Wine Grapes in South Africa

TABLE 9.1. Dry ball (T d

) and wet ball (T w

) temperatures for calculating dew point

temperature at different altitudes (A).

Wet ball temperature (°C)

A (m)

T d

-T w

(°C)

-2

-1

0

1

2

3

4

5

250 0.2 -2.3 -1.3 -0.3

0.7 0.3

1.7

2.7

3.7 3.4 2.8 1.5 0.1

4.7 4.4 3.8 2.6

0.5 -2.8 -1.8 -0.7

1.3 2.3

1.0 -3.7 -2.6 -1.5 -0.5

0.6

1.7 0.3

2.0 -5.7 -4.5 -3.2 -2.0 -0.9 3.0 -8.0 -6.6 -5.2 -3.8 -2.5 -1.2 1.3 4.0 -10.8 -9.0 -7.4 -5.8 -4.3 -2.9 -1.5 -0.1 5.0 -14.2 -12.0 -10.0 -8.2 -6.4 -4.8 -3.2 -1.6 7.0 -25.8 -21.1 -17.4 -14.4 -11.8 -9.4 -7.3 -5.3 9.0 – – -36.9 -26.5 -20.7 -16.5 -13.1 -10.3 11.0 – – – – – -33.0 -23.5 -17.9 500 0.2 -2.3 -1.3 -0.3 0.7 1.7 2.7 3.7 4.7 0.5 -2.8 -1.8 -0.7 0.3 1.3 2.4 3.4 4.4 1.0 -3.7 -2.6 -1.5 -0.4 0.7 1.7 2.8 3.9 2.0 -5.6 -4.4 -3.1 -1.9 -0.8 0.4 1.5 2.7 3.0 -7.8 -6.4 -5.0 -3.7 -2.3 -1.1 0.2 1.4 4.0 -10.4 -8.7 -7.1 -5.6 -4.1 -2.7 -1.3 0.1 5.0 -13.6 -11.5 -9.6 -7.8 -6.1 -4.5 -2.9 -1.4 7.0 -24.0 -19.8 -16.5 -13.6 -11.2 -8.9 -6.8 -4.9 9.0 – -81.6 -31.9 -24.1 -19.2 -15.4 -12.2 -9.5 11.0 – – – – -18.6 -28.5 -21.3 -16.4 750 0.2 -2.3 -1.3 -0.3 0.7 1.7 2.7 3.7 4.7 0.5 -2.8 -1.7 -0.7 0.3 1.3 2.4 3.4 4.4 1.0 -3.6 -2.5 -1.4 -0.4 0.7 1.8 2.8 3.9 2.0 -5.5 -4.3 -3.0 -1.9 -0.7 0.5 1.6 2.8 3.0 -7.6 -6.2 -4.8 -3.5 -2.2 -0.9 0.3 1.5 4.0 -10.1 -8.4 -6.9 -5.4 -3.9 -2.5 -1.1 0.2 5.0 -13.1 -11.1 -9.2 -7.5 -5.8 -4.2 -2.7 -1.2 7.0 -22.5 -18.7 -15.6 -12.9 -10.6 -8.4 -6.4 -4.5 9.0 – -41.2 -28.5 -22.2 -17.8 -14.4 -11.4 -8.9 11.0 – – – – -36.3 -25.3 -19.4 -15.1

1 000 0.2 -2.3 -1.3 -0.3

0.7 1.7

2.7 2.4 1.8 0.6

3.7 3.4 2.9 1.7 0.4

4.7 4.4 3.9 2.8 1.7

0.5 -2.7 -1.7 -0.7

0.3

1.4 0.7

1.0 -3.6 -2.5 -1.4 -0.3

2.0 -5.4 -4.1 -3.0 -1.8 -0.6 3.0 -7.4 -6.0 -4.7 -3.4 -2.1 -0.8 4.0 -9.8 -8.2 -6.6 -5.1 -3.7 -2.3 -0.9 0.4 5.0 -12.7 -10.7 -8.9 -7.1 -5.5 -3.9 -2.4 -1.0 7.0 -21.2 -17.8 -14.8 -12.3 -10.0 -7.9 -6.0 -4.2 9.0 – -34.6 -25.9 -20.6 -16.7 -13.4 -10.7 -8.2 11.0 – – – – -30.9 -22.9 -17.8 -13.9

288 CHAPTER 9 – PREVENTING COLD DAMAGE IN VINEYARDS