Grasslands of the World.pdf - Disasters and Conflicts - UNEP

Grasslands of South Africa 83
CLIMATE
Rainfall
With a mean annual rainfall of approximately 450 mm, South Africa is regarded
as semi- arid . There is wide regional variation in annual rainfall (Figure 3.4),
from 3 000 mm
in the mountains of the south western Cape. However, only 28 percent of the
country receives more than 600 mm (Table 3.1).
The uncertainty of the rainfall is best expressed by the coefficient of variation
in annual rainfall (Figure 3.5). The low rainfall regions have the highest
coefficient of variation and drought is common. Annual rainfall distribution
is skewed such that there are more below-average than above-average rainfall
years, and the median is more meaningful than the mean. The high seasonal
variations are accompanied by high spatial variability, and the annual potential
evapotranspiration (PET) may exceed annual precipitation by ratios of up to
20:1, hence drought conditions are a common phenomenon (Schulze, 1997).
The declaration of drought status to a magisterial district has historically
been used by the Department of Agriculture and Land Affairs to intervene in
Figure 3.4
The median annual rainfall for South Africa .
SOURCE: Dent, Lynch and Schulze, 1987.
TABLE 3.1
Annual rainfall distribution and climatic classification in South Africa
Rainfall (mm) Classification Percentage of land surface