Numerical study of a Saharan dust plume impact on radiation, urban climate and thermal comfort in the Paris region during an heatwave event

In Europe, heatwave conditions associated with southern synoptic flows can sometimes be combined with episodes of dust plumes coming from the Saharan desert. Change in the atmospheric composition of aerosols alters the radiation observed near the ground, resulting in impacts on other variables such as air temperature. This study focuses on the heatwave experienced by the Paris region from 15 to 19 June 2022, combined with the passage of a Saharan dust plume. To investigate the aerosols impact on local weather conditions and thermal comfort, three Meso-NH atmospheric numerical simulations are used: one without dust aerosol (C0), one with dust aerosols defined from CAMS reanalysis (C1), and one with twice the concentration of CAMS dust aerosols (C2). Simulation C1 is validated against observations from the PANAME-Urban experimental campaign. The time evolution of Aerosol Optical Depth and incoming solar radiation at the surface is well reproduced, with improvement in the resulting air temperature and boundary layer height when taking aerosols into consideration. The radiative effect of dust aerosols results in a decrease in incoming solar radiation and air temperature of up to 75 W m −2 and 1 °C, respectively. At 16:00 UTC, it results in a thermal comfort improvement of up to 1 °C in sunny urban and suburban areas. However, in shaded suburban areas, the increase in diffuse solar radiation and humidity and the decrease in wind speed induced by the dust aerosols counterbalance the air temperature decrease, resulting in no thermal comfort improvement. This result highlights the need to integrate these insights into operational heat-health warning systems – by coupling aerosol forecasts with bioclimatic indices.