The mean annual precipitation (MAP, in mm) characterises the long-term quantity of water available to a region for hydrological and agricultural purposes, and is one of the most used statistics in crop production.
Note that while simple to calculate and attractive to use, the concept of MAP nevertheless has its weaknesses, in that in this region (and elsewhere in South Africa) years with lower than average rainfall are more numerous than years with higher than average rainfall. This is because MAPs are frequently inflated by a few very high annual totals from very wet years, especially in areas of low rainfall.
MAP was obtained using methods described in the section Background: Climate Change Modelling. This resulted in a unique 50-year daily rainfall record for each of the Quinaries covering the region (Schulze et al., 2010).
Future rainfall projections remain challenging and are not presented here. This is because:
- Rainfall is a derived rather than a direct output from GCMs.
- Complex rainfall-generating processes such as cloud formation and land surface-atmosphere interactions are not yet fully understood and resolved in climate models.
- Rainfall is an event based variable, and not continuous, as is temperature.
As the climate model developers address the weaknesses and inconsistencies in the older GCMs, the new set of GCMs can alter the picture somewhat. The future rainfall maps can be presented once there is a greater model agreement and confidence in the results.