PS 44-186 - Investigating drivers of increased risk of dust emission in the Four Corners using ecological monitoring and satellite data.

Abstract: Wind erosion and dust emission from drylands have large consequences for ecosystems, society, and human health. During spring in the western United States, dust emitted from drylands of the Colorado Plateau that is transported to snowpack in the Southern Rockies changes snow surface albedo, altering regional hydrology and threatening water resources. Dust emission is physically controlled in part by nonerodable surface roughness elements like plants, which attenuate wind shear stress at the soil surface and physically protect part of the surface from wind erosion. Thus, changes in plant cover and structure can have a large influence on the potential for dust emission from drylands. However, multiple factors can drive plant community change. In this study, our objective was to determine whether recently detected trends in surface roughness from 2001 to 2020 have been driven primarily by climate, land management, or their interaction. We first modeled surface roughness for the Four Corners region from the Moderate Resolution Imaging Spectroradiometer (MODIS) albedo product (MCD43A3; daily 500-m). We then identified where springtime surface roughness had significantly changed from 2001-2020 using Mann-Kendall trend analysis. Next, we described the abiotic and biotic conditions of the study region using gridded climate and soil-geomorphic maps, percent cover data of bare soil and plant functional groups using remote sensing products (LandCART), and cluster analysis in Google Earth Engine to create hypothesized ecological states. Finally, we assessed relative change in percent cover of each ecological state from 2001-2020 and compared them to overlapping trends in surface roughness and long-term drought (1995-2020) using Theil-Sen regression. Our results showed that state changes and drought were both strong drivers of surface roughness change. Also, drought trends had a relatively weak effect on state change, which suggests that other factors are driving reductions in surface roughness in rangelands, likely changing land use and fire. This is most evident among croplands and fire scars, but our data suggest that continuous land uses like livestock grazing may also play a role in surface roughness reduction. Moreover, our results indicate that even in areas experiencing long-term droughts that can change vegetation communities, land uses can be strong drivers of ecological changes that influence aeolian processes. This suggests that dust emission and its subsequent downwind impact on snow hydrology could be mitigated with land management practices that maintain ground cover and avoid ecological transitions to more patchy plant communities that less effectively protect erodible soils.