Figure 3.7 indicates that South Africa has a mean annual precipitation (MAP) to mean annual runoff (MAR) ratio of 8.6%, that is, only 8.6% of the rainfall is available as surface water. This is one of the lowest conversion ratios in the world.

Canada and Australia, which have similar MAP figures, have ratios of 65.7% and 9.8% respectively.

The MAR for South Africa is estimated at 50 150 million m³ a^-1. This is not distributed evenly throughout the country, with the Eastern seaboard having high runoff, whilst the western regions tend to have low runoff (Figure 3.8.)

Nor is it consistent over time, with great variability between years (Figure 3.3 a-e).

Groundwater:

Similar to surface waters, South Africa'sgroundwater resources are relatively limited compared to world averages Figure 3.9 (E Braune,DWAF pers. comm.)

Of critical importance is the relationship between groundwater and surface water. Groundwater can only be abstracted on a sustainable basis at a rate less than, or equal to, its long-term average recharge through infiltration of rainwater. Already many of the streams that existed at the beginning of the century have dried up due to over-extraction, and groundwater failure is common in some of the more densely-populated areas (Basson et al. 1997).

There are an estimated 50 000 new boreholes drilled in South Africa per year by the private sector, but the majority are dry or low yielding (E Braune,DWAF, pers. comm.). Figure 3.10 shows the growth in number of boreholes registered on the National Groundwater Database. The present figure (1999) is 197 811 extant boreholes.

Wetlands are some of the most threatened aquatic habitats in South Africa (Walmsley 1991) . Threats to wetlands include human development activities, channelisation, drainage, crop production, effluent disposal and water abstraction; that is, most human-induced land-use changes (see Terrestrial Ecosystem section). Begg (1986) states that "wetlands formerly occupied between 10 and 15% of every catchment in Natal.

Within the last fifty years wetlands in these same areas have been reduced to a few scattered remnants, and in certain catchments virtually eliminated". This probably applies to the rest of South Africa, but little information is available about the extent of previously-existing wetland areas.

Even the present DEA&T database on wetlands is limited to 1 377 wetlands as shown in Figure 3.11. Of these, 21% are marine and estuarine, 21% are endorheic pans, 15% are riverine, 5% are lacustrine, 19% are palustrine, and 18% are man-made (Cowan and Van Riet 1998). Of the 829 naturally-occurring freshwater wetlands, 13.5% have full protection within a national park, provincial nature reserve or wildlife sanctuary and 3.9% are partly protected (Cowan and Van Riet 1998).