Threshold wind velocity as an index of soil susceptibility to wind erosion under variable climatic conditions

Wind erosion starts when the threshold wind velocity ( µ t ) is exceeded. We evaluated the sensitivity of µ t to determine the wind erosion susceptibility of soils under variable climatic conditions. Three years field data were used to calculate µ t by means of the equation µ t = ū ‐ σ Φ −1 ( γ ), where ū is the mean wind speed (m s −1 ), σ the ū standard deviation (m s −1 ), γ the saltation activity and Φ the standard normal distribution function of γ . Saltation activity was measured with a piezoelectric sensor (Sensit). Results showed that ū of the whole studied period (3·41 m s −1 ) was lower than µ t (7·53 m s −1 ), therefore, wind erosion was produced mainly by wind gusts. The µ t values ordered in the sequence: Winter (6·10 m s −1 ) < Spring (8·22 m s −1 ) = Summer (8·28 m s −1 ) < Autumn (26·48 m s −1 ). Higher µ t values were related to higher air humidity and lower wind speeds and temperatures. The µ t values did not agree with the erosion amounts of each season, which ordered as follows: Summer (12·88 t ha −1 ) > Spring (3·11 t ha −1 ) = Winter (0·17 t ha −1 ) = Autumn (no erosion). Low µ t and erosion amounts of Winter were produced by a scarce number of gusts during eroding storms. We concluded that µ t is useful as an index of soil susceptibility to wind erosion of different climatic periods. The use of a unique µ t value in wind erosion prediction models can lead to erroneous wind erosion calculations.