We can confidently predict that a warmer world, overall, will be wetter. All the prehistoric data, such as reduced rainfall during past glacial periods, show this, as do all climate models. However, for some specific regions, including parts of Southern Africa, this will not necessarily be true. The belt of arid lands north and south of the tropics is likely to become drier even as the rest of the world becomes wetter. The details of future trends in rainfall at local scale are much harder to predict than, for instance, the future rise in temperature. The pattern of rainfall over South Africa during the past century provides no widespread, clear evidence of change, either up or down. Climate modellers deal with the variation between model predictions by calculating averages over a large number of runs of different models, called ensembles.

Broadly speaking, the future geographical distribution of rainfall in South Africa is likely to be similar to the present pattern, only more so – thus dry places are projected to get drier and wet places may get wetter.

Most of Southern Africa will remain a predominantly summer rainfall area. It is believed that the south-western Cape will remain a predominantly winter rainfall area, but may see some decreases in rainfall overall, with small increases in summer rainfall. Summer rainfall in the fynbos biome could be ecologically damaging – the main reason why there are so few grasses in the fynbos is the long, dry summers. Invasion of grasses taking advantage of wetter summer conditions would change the historical fire pattern from intense fires once every ten to twenty years, which fynbos needs to maintain plant diversity, to less intense but more frequent grass-fuelled fires.

The southern and eastern Cape represent a transition zone between the summer and winter rainfall regions. Changes in extreme rainfall events may be quite dramatic here.