Are climate and land cover changes in East Asia important factors for dust emission variability in the past 30 years?

Abstract:

Mineral dust is important for climate because it alters the radiation budget, both directly by scattering sunlight and indirectly by influencing cloud processes. Studies have shown that the variability of dust emission is greatly affected by local wind speeds and land surface characteristics. Globally, land cover change is mainly driven by vegetation changes that modify the dust sources, which can be represented by changes in leaf area index (LAI), and its effect on East Asian dust emission under the backdrop of changing wind patterns has yet to be quantified. Here we present a study to investigate how climate and land cover changes might have modified dust emission in East Asia during 1982-2010 using the GEOS-Chem chemical transport model. New developments include a dynamic geomorphology-dependent dust emission scheme and better representation of vegetation effect on surface roughness and threshold wind speed. We also implement subgrid wind variability to reduce the resolution dependence of the model. The bias of modeled total aerosol optical depth (AOD) relative to observations is reduced from about -86% to -14%, mostly due to the inclusion of subgrid wind variability, but up to 10% of the emission improvements stem from the revised vegetation dependence. Simulations suggest that about 45 Tg, ~9% of the global dust emission, is from East Asia in spring. Sensitivity studies with changing historical LAI vs. surface wind show that climate variability might be a more important factor than land cover change contributing to dust emission variability and trends over the past 30 years.