Response of Dust Emissions in the Southwestern North America to Trends in Vegetation Cover over the Twenty-First Century: Implications for Air Quality

Fine mineral dust is known to cause adverse consequences for human health and visibility. Climate models predict a shift toward warmer and drier environments in southwestern North America. However, projected dust trends under the warmer and drier conditions are controversial, in part due to uncertainties in the response of vegetation cover to future climate scenarios. Many previous studies have not taken land cover or land use change into account. Here we implement a coupled modeling approach to assess the impacts of future changes in climate and land use practices on dust mobilization, and we investigate the consequences for surface air quality. We rely on the Lund-Potsdam-Jena (LPJ) dynamic vegetation model and the chemical transport model GEOS-Chem to examine trends across the 21^st century for different Representative Concentration Pathways (RCPs). We probe the impact of future meteorology on changes in vegetation type, leaf area indices (LAI), and soil characteristics using the LPJ following three scenarios: 1) the all-factor scenario that includes changes in climate, land use, and CO₂ fertilization; 2) the fixed-CO₂ scenario that includes changes in only climate and land use; 3) the fixed-land use scenario that includes changes in only climate and CO₂. We then derive dust emissions under these distinct future scenarios to distinguish the effects of different drivers. The fine-scale, nested version of GEOS-Chem allows us to link trends in dust to human exposure at the county scale. Considering all factors in the worst-case scenario (RCP8.5), we find decreasing trends of fine dust emissions over Arizona and New Mexico but increasing emissions along Mexico's northern border in the late-21^st century during springtime, which is the peak dust season. LPJ simulates more densely vegetated environments in arid lands under future climate scenarios, including Arizona, New Mexico, and Texas, where dust is especially prevalent, but sparser vegetation in Northern Mexico. The two main drivers of trends in dust, CO₂ fertilization and land use practices, play opposing roles. Anthropogenic land use increases dust in Northern Mexico, while CO₂ fertilization enhances vegetation and thus decreases dust in Arizona, New Mexico, and Texas. Our work emphasizes the importance of land cover change as a key driver of future dust emissions, and provides a resource for environmental managers to better prepare for the air quality challenges in a changing world.