Wind speed trend analysis and inter-annual variability in South Africa

Abstract

Precise projections of long-term linear wind speed patterns provide a useful predictor of shifts in air circulation. Additionally, they are vital for the planning and financing of sectors such as wind power. Trend analysis and inter-annul variation (IAV) of wind speed were executed to examine longterm wind speed patterns and variations in historical mean wind speed data as an index of climate change in South Africa. The examinations were performed on annual mean wind speed data. The variations and patterns, however, are not the result of one factor. They are the result of the interactions of several climatic elements and variables. Thus, the study of wind speed patterns reveals climatic changes. The data used for the analysis was obtained from Wind Atlas of South Africa’s (WASA) website. WASA collected data since 2010 at 19 metrological stations (WM01-WM19). Trend analysis was performed using the nonparametric Mann-Kendell’s test. The results showed an increasing trend at WM01 and a decreasing trend at WM08. There were no trends at other stations. From the trend analysis results, the magnitude at which wind speed changes per year for the period in investigation varied between 0.003 and 0.111 m/s/year. The lowest change was at WM05, and the highest at WM11. IAV values were calculated by dividing the standard deviation of the annual mean and long-term mean wind speed. IAV values ranged between 1.088% and 3.353%. The industrial standard is 5.4%, but in South Africa it is between 2% and 6% in the study that was conducted in 2019. Stations that had IAV values below 2% are WM03, WM09, WM10, WM14 and WM15, and that implies that the degree at which mean annual wind speed changes at these stations is low. It is recommended that further work be done with long term period (e.g. 20 years).