1.0

This polygon layer has been converted from a grid of mean annual runoff for South Africa (mm/year for each 1 x 1 minute grid cell), using all values = 135 mm/year. The mean annual runoff data is also on BGIS (MAR_SWSA) and is based on disaggregating the Water Resources Assessment 2005 data (Middleton and Bailey 2009), which represents the most commonly-used national mean annual runoff data used by the Dept of Water Affairs for water resources planning and management. This data layer was used to identify Strategic Water Source Areas for South Africa. Strategic Water Source Areas are those areas that supply a disproportionate amount of mean annual runoff to a geographical region of interest.

TODO: please complete per data partner / dataset

This map is a polygon version created by extracting all grid cells in MAR_SWSA (also on BGIS) with = 135 mm/year and converting them to polygons. The original MAR_SWSA was created using the Water Resources of South Africa data (WR2005) for Mean Annual Runoff at a quaternary catchment scale (Middleton and Bailey 2009), which was then disaggregated to a 1 x 1 minute grid resolution using a set of generalised rainfall-runoff relationships provided by Pitman (1996) and used in the WR90 project (Midgley et al. 1994). The polygons here of Strategic Water Source Areas was produced by grouping areas generating mean annual runoff across South Africa, Lesotho and Swaziland into percentile categories, where areas representing 50% of the mean annual runoff in the region were considered to be Strategic Water Source Areas for the country. The polygons of these areas is given in this data layer. These areas in South Africa, Lesotho and Swaziland together contribute 50% of the region’s water supply in less than 8% of the land surface area.

Available documentation:

Nel, J.L, Colvin, C., Le Maitre, D.C., Smith, J. and Haines, I. 2013. South Africa’s Strategic Water Source Areas.

CSIR Report CSIR/NRE/ECOS/ER/2013/0031/A, CSIR, Stellenbosch, South Africa.

SANS 1878

FGDC-STD-001-1998