The effect of wind speed averaging time on sand transport estimates

Wind speed changes continuously in nature, but the characteristics of those changes differed among different time scales. Small-scale variations in wind speed mainly represent the instantaneous characteristics of the wind, whereas wind speed on larger scales can be used to estimate the average sand transport rate and soil erosion. The mean wind speed changes greatly as the averaging time used to calculate the mean changes, leading to different estimates of sand transport. In this study, we compared wind speed distribution and the total sand transport calculated using different averaging times (1, 2, 5, 10, 30, and 60 min, respectively). Different time scales produced significant differences in wind speed distribution and in the estimate of wind erosion. As the averaging time increased, the wind speed data series became smoother, peaks became smaller, and the wind speed distribution got narrower. Compared with sand transport calculated from the 1-minute mean wind speed data, all transport values were lower when calculated with averaging times of 2, 5, 10, 30, and 60 min. Thus, averaging the wind speed functions as a “smoothing filter” that tends to eliminate at least some of the high-frequency and low-frequency variability. It therefore affects the estimates of the real wind speed and of the transport and deposition of wind-blown sand. However, sand transport can be converted from the values calculated from different averaging times to a 1-min scale by making use of the conversion equation. Further studies are needed to apply and extend the present findings to improve the prediction of wind erosion.