Adrian Chappell

and 17 more

Vegetation is a major control on dust emission because it extracts momentum from the wind and shelters the soil surface, protecting dry and loose material from erosion by winds. Many traditional dust emission models (TEMs) assume that the Earth’s land surface is devoid of vegetation, adjust dust emission using a vegetation cover complement, and calibrate the magnitude of modelled emissions to atmospheric dust. We compare this approach with a novel albedo-based dust emission model (AEM) which calibrates Earth’s land surface normalised shadow (1-albedo) to shelter depending on wind speed, to represent aerodynamic roughness spatio-temporal variation. Existing datasets of satellite observed dust emission from point sources (DPS) and dust optical depth (DOD) show little spatial relation and DOD frequency exceeds DPS frequency by up to two orders of magnitude. Relative to DPS frequency, both dust emission models showed strong relations, but over-estimate dust emission frequency, suitable for calibration to observed dust emission. Our results show that TEMs over-estimate large dust emission over vast vegetated areas and produce considerable false change in dust emission, relative to the AEM. It is difficult to avoid the conclusion, raised by other literature, that calibrating dust cycle models to atmospheric dust has hidden for more than two decades, these TEM modelling weaknesses and its poor performance. The AEM overcomes these weaknesses and improves performance without masks or vegetation cover. Considerable potential exists for Earth System Models driven by prognostic albedo, to reveal new insights of aerosol effects on, and responses to, contemporary and environmental change projections.

Tarek Kandakji

and 2 more

Quantifying the effect of anthropogenic land use change on dust emission is a contentious issue. In this research, 1508 dust point sources were detected in the Southern High Plains and Chihuahuan Desert regions of the United States for 2001-2016, encompassing a period of extreme drought. These points were subjected to quantitative and spatio-temporal analysis. Point pattern analysis showed a significant cluster of these points in West Texas (Nearest Neighbor Ratio = 0.33, р < 0.001) where cultivated lands and grasslands are dominant land cover. Spatial observation suggests that the geographic center of dust points in these regions shifts away from bare soil and shrublands toward grasslands and cultivated lands as drought level increases, while it shifts away from grasslands and cultivated lands towards bare soil and shrublands in cases of no drought. Chi-square test captured a significant association between land use type and drought level on dust emission (χ2 (6) = 47.33, р < 0.001). However, Cramer’s V value (0.13, р < 0.001) indicates that the association captured by the chi-square is weak, suggesting that other factors, perhaps meteorological variables, are at play in the spatial distribution of dust sources in this region. The proportion of dust points differs significantly during severe/exceptional droughts versus no drought or abnormally dry/moderate drought in both cultivated lands and grasslands. The proportion of dust points in bare lands and shrublands, however, did not significantly change between no drought and severe-exceptional drought. These results suggest anthropogenic land use in southwestern U.S. is significantly associated with drought in terms of dust emission. Human activity amplifies of the effects of drought by increasing soil erodibility; thus, adopting land management practices to resist wind erosion is crucial. Further investigations on a global scale should provide more information on this association.