Spatiotemporal dynamics of shear stress partitioning around vegetation in a sparsely vegetated dryland

Abstract. Vegetation is the dominant regulator of wind erosion and dust emission in drylands. Drag partition theory is typically used to quantify how vegetation reduces surface shear stress, but lateral flow acceleration along plant sides and the resulting spatiotemporal patterns of shear stress redistribution around individual plants in the field remain understudied. Here we quantify the surface shear stress ratio, its spatial and temporal variability, and lateral flow acceleration along the side of a shrub across a range of wind magnitudes and phenological phases. The spatial variability of the surface shear stress ratio exceeded that reported previously, whereas the temporal variability was 75 % of the spatial variability. Along the shrub side, surface shear stress ratio was independent of wind speed and exhibited a statistically significant decreasing trend with foliar growth while maintaining pronounced spatial heterogeneity, including localized shear amplification near shrub margins. The shape and position of the acceleration zone was broadly consistent with prior studies, although uncertainties remain regarding how vegetation type and dimensional traits influence its extent and form. Incorporating phenology-dependent, yet wind speed-independent, shear stress redistribution and spatiotemporal variability into drag partition schemes provides a pathway toward improved process-based representation of vegetation-wind interactions in wind erosion models. This refinement could improve predictions of the timing, location, magnitude, and frequency of aeolian sediment transport and dust emission, including low-intensity events when above-canopy winds are near or below conventional thresholds.