Layer: Strategic Water Source Areas Aquatic (ID: 9)

Parent Layer: Aquatic Biodiversity Theme

Name: Strategic Water Source Areas Aquatic

Display Field: swsa_name

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Description: 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.

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Shape ( type: esriFieldTypeGeometry , alias: Shape )
swsa_name ( type: esriFieldTypeString , alias: swsa_name , length: 30 )
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