Seasonal variations in threshold wind speed for saltation depending on soil temperature and vegetation: A case study in the Gobi Desert

The threshold wind speed for saltation ($U_t$), an index of soil susceptibility to wind erosion, is affected by dynamics of various land surface conditions. Little information is available on the primary factors that affect $U_t$ in the Gobi Desert. This study explored seasonal variations of $U_t$ and its relations with land surface conditions at Tsogt-Ovoo, which is a dust source hotspot in East Asian drylands, based on a 6-year (2012–2017) measurement. The land surface parameters (soil moisture and temperature, and vegetation components of live, standing dead, and litter) were simulated by an ecosystem model. Results show that saltation tended to occur during February–June under strong western winds (>10 m s⁻¹), with the highest frequencies in 2012 and 2015. The saltation season was divided into two periods: spring (February–early May) with an increase in saltation (i.e., a decrease in $U_t$); and early summer (late May–July) with a decrease in saltation (i.e., an increase in $U_t$). For 2012 and 2015, multi-regression analysis reveals that $U_t$ negatively correlated with soil temperature in spring (R²_adjusted = 0.39) and positively with vegetation components of live and standing dead in early summer (R²_adjusted = 0.70). We assume that wind erosion was possibly enhanced through soil freeze–thaw processes and then was suppressed through plant growth in addition to dead leaves that were residues from the preceding summer. We establish a statistical model of $U_t$ for this hotspot to analyze the relative contributions of erosivity and erodibility to wind erosion during 2012–2017.