Fig. 4 Relationships between wind erosion, and temperature and precipitation in southern Africa due to temporal changes in the (a) mean annual temperature and (b) annual precipitation. Spatial distributions of (c) mean annual temperature and (d) annual precipitation. Spatial patterns of the partial correlations between wind erosion, and (e) mean annual temperature and (f) annual precipitation.
The annual maximum wind speed in southern Africa showed a clear downward trend from 1991 to 2015, with a decline rate of 0.0742 m/s/a (r² = 0.87, p < 0.01) (Fig. 5a). A significant drop in the wind speed led to a reduction in soil wind erosion (Fig. 3a). There was a significant positive correlation (p < 0.1) between the annual wind erosion modulus and the annual average maximum wind speed across 68.18% of southern Africa (Fig. 5b), mainly distributed in the Kalahari Basin of South Africa and southern Botswana. A slight rise in wind speed in 2003–2004 and 2006–2007 led to an increase in the average annual wind erosion modulus, which suggested that wind speed had a strong influence on wind erosion spatial distribution and temporal changes. However, near-surface wind speed is not the main factor affecting soil erosion in the Western Coastal Namib area where the soil erosion is more likely to be affected by the surface rock structure and lower vegetation coverage.