WRF-CHEM Simulations of Saharan Dust for the Periods of 1981–2010, 2041–2060, 2081–2100 Using NCEP, ECMWF Reanalyses, and the CMIP5/CMIP6 GCMS

The Sahara Desert is the largest source of aeolian dust with high annual transport across West Africa, Europe, the Caribbean and United States, which affects air-quality, and poses a health risk to many communities. Global Climate Models (GCMs) are used to project future climate under different representative concentration pathway or shared socioeconomic pathway (SSP) scenarios; however, their coarse resolution has challenges in resolving primary dust emission locations over North Africa. In this study, we drive the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-CHEM) using European Centre for Medium-Range Weather Forecasts (ECMWF), National Center for Environmental Prediction (NCEP), and the Coupled Model Inter-comparison Project Phase 5 or 6 (CMIP5; Geophysical Fluid Dynamics Laboratory Earth System Model version 2M (GFDL-ESM2M), CMIP6; Max Planck Institute Earth System Model (MPI-ESM)) GCMs at the lateral boundaries for 1981–2010 (ECMWF–WRF, NCEP–WRF, MPI–WRF, and GFDL–WRF simulations respectively) and in the future time period during the mid and late 21^st century (2041–2060 and 2081–2100 respectively) under two different scenarios (i.e., SSP1–2.6 or RCP–2.6 and SSP5–8.5 or RCP–8.5) at 20 km grid spacing. We evaluated the annual and seasonal biases in Particulate Matter (PM₁₀ and PM_2.5) and the low-level circulation during the historical period (1981–2010). The preliminary results reveal similar seasonal variability of dust concentrations between the WRF-CHEM simulations and surface observations over the Sahel but show large biases in terms of the magnitude during winter due to biases in the surface circulation. We will also evaluate MPI-WRF, GFDL–WRF, ECMWF–WRF, and NCEP–WRF simulated Aerosol Optical Depth (AOD) against MODIS, CALIOP or MISR AOD during the early 21^st Century. Finally, we compared the future PM concentrations for the periods of 2041-2060 and 2081–2100 under both SSP1–2.6 (or RCP–2.6) and SSP5–8.5 (or RCP–8.5) forcing to the base period of 1981–2010, and our preliminary results show high dust concentrations in the future for mid-century scenarios driven by strong winter season Libyan and Azores high pressure systems and the summertime Saharan heat low. Projections of warmer climates and higher dust concentrations in the future will lead to negative health outcomes in West Africa.