63e8961f-fdfa-4847-a450-8461e5e58462 SANBI The Metadata Manager +27 21 799 8738 Kirstenbosch Research Centre Cape Town Claremont 7735 South Africa bgishelp@sanbi.org.za 2025-08-25T15:17:29 SANS 1878 FGDC-STD-001-1998 Albers 2021 Strategic Water Source Areas for surface water 2021 Strategic Water Source Areas (SWSAs) refer to the 10% of South Africa’s land area that provides a disproportionate 50% of the country’s water runoff. Understanding where these SWSAs are is crucial to planning and management of water resources, including the ecosystems that support water quality and quantity. These areas extend into Lesotho and eSwatini. National SWSAs for surface water have been delineated in various forms over the past 15 years, with increasing precision in each iteration. In 2018, 22 SWSAs were identified based on a generalised 1.7 x 1.7 km resolution Mean Annual Runoff dataset, providing a widely accepted product that gained strong traction with government and non-government audiences, proving effective for building awareness and integrating SWSAs in a range of national policies and frameworks. However, the coarse resolution does not align well with the scales used for implementation at catchment and local levels. So, using best available information and the latest geostatistical approaches, South Africa’s SWSAs for surface water have now been delineated at a finer resolution of 90 x 90 m. The work, which concluded in 2021 resulted in two products (both explained in greater detail in Lotter & Le Maitre (2021)): 1. A downscaled mean annual precipitation surface: through consideration of several explanatory variables in the modelling process (such as elevation, latitude, distance from coast, topographical positional index, and Mean Annual Runoff), the “new” Mean Annual Precipitation surface layer was “interpolated” using a dataset of over 8000 rainfall stations and a Shuttle Radar Topography Mission (SRTM) 90 m Digital Elevation Model (DEM) (available as a stand-alone product). 2. 2021 SWSA layer: This precipitation surface layer was used to delineate fine-scale SWSA boundaries, which were compared with the older 2018 SWSAs for surface water to maintain the 22 SWSAs with similar extent and location to those identified in the 2018 SWSAs. Delineating SWSAs at a finer scale was done across South Africa, Lesotho and eSwatini because of the shared water catchments that feed into water supply systems in South Africa. Both above mentioned layers therefore extend across the three countries. The 2021 spatial layer for SWSAs for surface water is a fine-scale delineation of the SWSAs, intended to support the integration of SWSAs in a range of catchment- and local-level planning, management, and regulatory processes. These include Catchment Management Strategies and their associated plans, land-use planning by municipalities, Environmental Impact Assessments and environmental authorisations, restoration projects undertaken through programmes such as Working for Water and Working for Wetlands, and expansion of South Africa’s protected area estate by conservation authorities. The 2021 SWSA for surface water layer is a refined spatial resolution of all the 22 SWSAs for surface water identified in 2018. It is not intended to be a revision of the 2018 SWSAs. It is intended to be integrated into a range of catchment- and local-level planning, management, and regulatory processes. Such as, in Catchment Management Strategies and their associated plans, in land-use planning by municipalities, in Environmental Impact Assessments and environmental authorisations, in restoration projects undertaken through programmes such as Working for Water and Working for Wetlands, and in expansion of South Africa’s protected area estate by conservation authorities (often in partnership with private and communal landowners). Mrs Precious Nokuthula Mahlangu South African National Biodiversity Institute (SANBI) Principal Researcher + 27 (21) 888 2407 Stellenbosch Stellenbosch Western Cape South Africa no.mahlangu2@sanbi.org.za Dr Mervyn Lötter Mpumalanga Tourism and Parks Agency Control Scientist: Biodiversity Planningng Pty Ltd Principal Hydrogelogist +27(0) 82 043 8075 Cape Town Office, 15 Bournemouth Road Muizenberg 7950 South Africa mervyn.lotter@mtpa.co.za Strategic Water Source Areas, surface water, Mean Annual Precipitation South Africa 10000 environment 2021-01-01 2021-01-01 15.292968749999995 33.486328125 -35.17380831799959 -21.616579336740585 SANBI bgishelp@sanbi.org.za ZIP 1 In 2004, the National Spatial Biodiversity Assessment (NSBA) 2004 included a map of the tertiary and quaternary catchments that jointly supply approximately 50% of the country’s water, referred to at that stage as “high water yield catchments”. In 2011, the National Freshwater Priority Areas (NFEPA) study identified sub-quaternary catchments with relatively high mean annual runoff as high-water yield areas. It also identified high groundwater recharge areas (Nel et al., 2011). In 2013, this work was taken further in a study by World Wide Fund for Nature South Africa (WWF-SA) and Council for Scientific and Industrial Research (CSIR) which identified 21 SWSAs for surface water which covered 8% of South Africa and supplied 50% of the mean annual runoff (Nel, et al 2013). These SWSAs for surface water (SWSA-sw) were included in the 2013 National Water Resources Strategy as areas needing protection for water security. Groundwater was not included in this study, although it is an important, and often the only, reliable water source in much of South Africa. In 2018, 22 SWSAs for surface water and 37 SWSAs for groundwater were identified (Le Maitre, et al 2018). The 22 SWSAs for surface water were identified based on a generalised 1.7 x 1.7 km resolution Mean Annual Runoff dataset, providing a widely accepted product that gained strong traction with government and non-government audiences, proving effective for building awareness and integrating SWSAs in a range of national policies and frameworks. However, the coarse resolution does not align well with the scales used for implementation at the catchment and local levels. The 2018 SWSAs excluded some catchment areas (Pondoland to Zululand coast) where the runoff was higher than the threshold because they were deemed water secure. It also added in three SWSAs (Waterberg, Upper Vaal, Upper Usutu) using a lower runoff threshold. These decisions were carried across into the fine-scale delineation process. In 2021, a new downscaled Mean Annual Precipitation of South Africa (refer to Lotter and Le Maitre 2021 for more details) and the latest geostatistical approaches were used to delineate South Africa’s SWSAs for surface water at a finer resolution of 90 x 90 m. The 2021 SWSAs for surface water were validated against the previous 2018 SWSAs for surface water. The fine-scale delineation is not intended to be a revision of the 2018 SWSAs. Instead, its primary purpose is to refine the spatial resolution such that SWSAs can be reliably integrated into a range of catchment- and local-level planning, management and regulatory processes. The 2021 SWSAs for surface water (Lotter and Le Maitre 2021) is now the best available layer for SWSAs for surface water. For SWSAs for groundwater, the best available layer remains the 2018 SWSAs for groundwater by Le Maitre et al 2018. The 2021 SWSAs for surface water were developed through the Biodiversity and Land Use (BLU) project, which was executed by SANBI in partnership with a range of public and private organisations and supported by the United Nations Development Programme (UNDP) and financed by the Global Environment Facility (GEF). Technical leadership for the work was provided by the Mpumalanga Tourism and Parks Agency, with technical review and input from experts on the SWSA Spatial Task Team. The technical report and finalisation and management of the spatial data were supported through the Ecological Infrastructure for Water Security (EI4WS) project, which is funded by the GEF, implemented by the Development Bank of Southern Africa (DBSA) and executed by SANBI in partnership with a range of private and public partners