This GIS layer represents the Strategic Water Source Areas (SWSAs) as “fuzzy blobs” for South Africa, Lesotho and Swaziland. Strategic Water Source Areas are those areas that supply a disproportionately high amount of the country’s mean annual runoff, in relation to their surface area, here defined as those areas that contribute >50% of the country’s mean annual runoff. These areas have been mapped for South Africa, originally derived from a 1 x 1 minute grid (MAR_SWSA) which is also on BGIS. They make up 8% of the land area across South Africa, Lesotho and Swaziland but provide 50% of the water in these countries. The intention of the SWSA_blobs layer is to denote fuzzy boundaries around general areas considered to be Strategic Water Source Areas, and to attach names to these “blobs”.

This GIS layer represents the Strategic Water Source Areas (SWSAs) as “fuzzy blobs” for South Africa, Lesotho and Swaziland. Strategic Water Source Areas are those areas that supply a disproportionately high amount of the country’s mean annual runoff, in relation to their surface area, here defined as those areas that contribute >50% of the country’s mean annual runoff. These areas have been mapped for South Africa, originally derived from a 1 x 1 minute grid (MAR_SWSA) which is also on BGIS. They make up 8% of the land area across South Africa, Lesotho and Swaziland but provide 50% of the water in these countries. The intention of the SWSA_blobs layer is to denote fuzzy boundaries around general areas considered to be Strategic Water Source Areas, and to attach names to these “blobs”.

This GIS layer represents the polygon layer for Strategic Water Source Areas (SWSAs) of South Africa, Lesotho and Swaziland. Strategic Water Source Areas are areas that supply a disproportionate amount of mean annual runoff to a geographical region of interest. National Strategic Water Source Areas were derived by grouping mean annual runoff in MAR_SWSA (also in BGIS) into categories representing 10, 30, 50, 75, 90 and 100% of South Africa’s water supply. Those areas supplying = 50% (which were represented by grid cells with = 135 mm/year) were taken to represent national Strategic Water Source Areas and converted to this polygon coverage. The mean annual runoff category, depicting grid cells that contribute > 50, 30 or 10% of the mean annual runoff are provided as attributes, as well as the name of the Strategic Water Source Area.

Grid cells with = 135 mm/year mean annual runoff that represent national Strategic Water Source Areas. These grid cells were extracted from MAR_SWSA (also on BGIS), which is the data layer for the mean annual runoff for South Africa (mm/year for each 1 x 1 minute grid cell), based on disaggregating the Water Resources Assessment 2005 data (WR 2005; Middleton and Bailey 2009). The WR 2005 data represents the most commonly-used national mean annual runoff data used by the Dept of Water Affairs for water resources planning and management.