The impact of ecosystem change on dust emission in North America

Authors: HENNEN, MARK - Cardiff University; CHAPPELL, ADRIAN - Cardiff University; WEBB, NICHOLAS - New Mexico State University

Submitted to: European Geosciences Union General Assembly Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/30/2020
Publication Date: 5/7/2020
Citation: Hennen, M., Chappell, A., Webb, N. 2020. The impact of ecosystem change on dust emission in North America. European Geosciences Union General Assembly Proceedings. 2020-21883. https://doi.org/10.5194/egusphere-egu2020-21883.
DOI: https://doi.org/10.5194/egusphere-egu2020-21883

Interpretive Summary: An estimated 50 Mt yr-1 of dust is emitted from North American landscapes, with profound regional impactson air quality and the resilience of ecosystems to land management and climate stressors. Vegetation types in different ecosystems protect the soil surface from erosive winds. In the dry western US, diverse land use and management drivers create disturbances that produce diverse ecosystem responses that can affect rates of wind erosion and dust emission. Identifying how ecosystem changes influence wind erosion and dust emission is needed to inform selection of conservation practices. To address this need, we produced the first moderate (500 m) resolution daily maps of dust emission across the western United States. These maps were based on estimates of wind erosivity at the soil surface derived from MODIS albedo data and using a regional dust model. We produced a North American dust emission climatology from 2001-2018 and evaluated the occurrence of dust emission across land use and land cover types within different ecoregions. We described the temporal patterns and seasonality of dust emissions and identified areas where changes in dust emission are occuring due to changes in vegetation communities responding to different land use and management systems.

Technical Abstract: An estimated 50 Mt yr-1 of dust is emitted from North American landscapes, with profound regional impacts (Shao et al., 2011). Dust emission flux in North America is controlled by wind speed and land surface (aerodynamic) roughness that are variable in both space and time. Vegetation growth, form and spatial distribution characterise different ecosystem regimes and protect the soil surface from the shearing stress of the wind. In the dry western US, diverse land use and management drivers create disturbance regimes that produce diverse ecosystem responses that could be drastically impacting rates of wind erosion and dust emission (Ravi et al., 2010). Resolving the impacts of ecosystem change on aeolian processes is needed to quantify anthropogenic-induced dust loads and identify management options as environmental solutions (Webb and Pierre, 2018). Currently, erosion surfaces in North America are derived from satellite imagery, either by spatial analysis of mean aerosol optical depth concentrations (e.g. Ginoux et al., 2012) or point source identification through subjective analysis of individual daily multispectral images (e.g. Lee et al., 2012; Kandakji et al., 2020). In either approach, the results are subjected to spatial and temporal bias caused by a lag in emission-to-observation period and loss of data during cloudy (dust and meteorological) periods. To complement these approaches we produced the first moderate (500 m) resolution daily maps of dust emission across the dry western United States. These maps were based on estimates of soil surface wind friction velocity (us*) derived from MODIS albedo data (Chappell and Webb 2016) using a commonly applied model (Marticorena and Bergammetti, 1995). The North American dust emission climatology from 2001-2018 was compared with the us* data volume to identify the spatio-temporal occurrence of three key disturbance regimes: i) land clearing for energy infrastructure, ii) invasion of shrublands by exotic annual grasses that alter fire regimes, and iii) replacement of grasslands by invasive shrub species. Against this background we examine the state and transition of ecosystem change across these landscapes to understand the impact on current dust emission. We use these findings to comment on the implications for future dust emission and to encourage the development of this modelling approach in Earth System Models.