Extreme wind maps for WASA Phase 2 domain, South Africa

Metadata and further information

December 2018

METADATA
Data set name	Extreme wind maps for the WASA domain, South Africa
Data set date	December 2018
Data provider	SAWS and DTU Wind Energy
Contact persons	Andries Kruger (SAWS) or Xiaoli G. Lars?n (DTU)
Contact details	Andries.Kruger@weathersa.co.za (SAWS) or xgal@dtu.dk (DTU)
Data type	GIS maps (reolution:38 km for 10 min map and 81 point values for gust map, interpolation with kriging)
Data format	ArcGIS ENVI
File name(s)	10 minute map : WASA2 10min with legend.mpk Gust map : WASA2 gust map.mpk
Data origin	10 min: Model data output verified with measurements for KwaZulu-Natal, Free State, parts of Mpumalanga, Gauteng, Northern Cape and Eastern Cape provinces) Gust: Observational data and additional point values derived from modelling over escarpment and coastal regions.

DATA PARAMETERS
1:50 yr 10 min wind speed	1:50yr 10 min wind speed [ms1] @ 10 m above ground level (standard conditions)
1:50 yr gust speed	1:50yr 2-3s gust speed [ms1] @ 10 m above ground level (standard conditions)

COORDINATE SYSTEM
Projection	1994 Hartbeeshoek
Zone number	n/a

DETAILED NOTES

Purpose
This data set was created for the WASA Phase 2 project and the Department of Energy, South Af-rica. The extreme wind maps were developed for use for input to site-specific assessments of the 1:50 year extreme winds and can be used with e.g. WEng software.

Methodology
10 minute map: The map is developed from the Spectral Correction Method (SCM) applied to rea-nalysis data at a resolution of 38 km. These values were verified by estimations obtained from ob-servations from the weather station network of SAWS.
Gust map: Main input is 1:50 year gust estimations derived from measurements from the SAWS observation network. The following were considered:

The Coast: most stations along the KwaZulu-Natal coast estimate a 1:50 year gust in the region of 35 m/s, therefore 35 m/s or 36 m/s (as in the case of the SANS map) is appro-priate. Towards the south at the Eastern Cape coast wind speeds are somewhat higher and in northern KwaZulu-Natal somewhat lower.
Top of escarpment should be higher than 40 m/s, as indicated by measurement estima-tions and provision for conservativeness.
The interior, excluding the escarpment, influenced by thunderstorms and synoptic-scale systems to varying degrees - measurements provide most reliable input.
To accommodate the coastal values of 36 m/s and making the values at the escarpment not too high, a common interval of 4 m/s was used (32, 36, 40, 44 m/s).
Additional inserted values along the coast (36 m/s along most of the coast, but 40 m/s along the Eastern Cape coast) and at the escarpment (44 m/s) ensured that interpolation in these regions are more realistic.
The northern and north-eastern Free State indicate higher gust estimations than 40 m/s indicated by SANS map - allocated a value of 44 m/s.
43 weather stations, and 38 additional data points for realistic representation ? total:81 point values

Reference is made to the information and documentation available from www.wasa.csir.co.za.
Limitations
The accuracy is limited by the inherent uncertainties of estimations of extreme winds estimated for extended periods of time, whether through the application of statistical methods to measured data, or the methodologies applied in the modelling. However, for conservativeness the values make provision for perceived uncertainties to a large degree.

The maps were designed specifically for planning purposes and should be used with utmost care for design, development and detailed assessments of actual wind farms.

The Extreme Wind Maps for South Africa is a product of the Wind Atlas for South Africa project and is described further on the WASA download pages. Details of the scientific considerations and methods applied are available from the developers (contact details above), and has been published through a range of peer-reviewed papers.

1:50 year 10 minute wind speed (m/s)

1:50 yr gust speed (m/s)

Please choose the file you wish to download.