Investigation of the Sensitivity of the Dust Emissions to Changes in the Normalized Vegetation Index (NDVI) over the Middle East in the GEOS Global Model Simulations

Over the period of 2003 to 2012, the Middle East region experienced a positive trend in aerosol optical depth (AOD) confirmed by long-term observations from the ground-based Aerosol Robotic Network (AERONET) of sun photometers and the space-based Moderate-Resolution Imaging Spectroradiometer (MODIS). Our previous studies with the NASA Goddard Earth Observing System (GEOS) global Earth system model show that the observed trends are also reproduced in the version of the model that includes aerosol data assimilation, the MERRA-2 Reanalysis, and are mostly absent in the version of the GEOS model with no aerosol data assimilated, the MERRA-2 GMI Replay. The fact that the observed trends are not present without invoking aerosol data assimilation points out deficiencies in the forward model with respect to the aerosol module. In order to improve the capabilities of the forward model, we have analyzed the rate of change of important dust emissions parameters, finding that changes in the vegetation cover could be an important factor not considered in the current model simulations. In this study, we investigate the sensitivity of the dust emissions to observed changes in the normalized difference vegetation index (NDVI) over the Middle East region in the same period. Our results show that enhancing dust emissions over regions in the Middle East that exhibit a decrease of vegetation reduces the differences between model and observations. Finally, we discuss implications for improving the aerosol forward model.