Relationships of post-fire aeolian transport to soil and atmospheric conditions

Abstract

Aeolian transport is an important contemporary geomorphic process in semiarid cold deserts; most evi- dent when vegetative cover is temporarily eliminated by wildfire. The erodibility of recently burned sur- faces is not stable in time, and near-surface moisture is expected to affect erodibility prior to regrowth of vegetation. In this study we examine effects of soil and atmospheric moisture on wind erodibility of loess soil following late-summer (2007) wildfire at the US Department of Energy, Idaho National Laboratory in southeastern Idaho, prior to re-emergence of vegetation. We measured threshold wind velocities, soil vol- umetric water content, air temperature, relative humidity, and vapor density at two sites with severe and moderate burn intensity, respectively, and an unburned site. Results indicate that erodibility, as mea- sured by threshold wind velocities, decreased with time following fire. Little sediment transport was detected at the unburned site and erodibility could therefore not be determined. Multiple regression models with predictors including soil water, atmospheric moisture, and time variables explained 83% and 69% of the variability in erodibility at the severe and moderate burn intensity sites, respectively. Erodibility decreased as soil volumetric water content increased to 15-20%, but was less responsive to further wetting. Erodibility predominantly decreased as atmospheric moisture increased, however, rela- tionships were complex. Multiple regression coefficients indicated erodibility increased as relative humidity increased at timescales of days-months. Positive and negative relationships were observed between erodibility and atmospheric moisture, within individual saltation events. Atmospheric and soil moisture appear important for post-fire wind erosion before re-establishment of vegetation.