The role of moist convection and haboobs in climate change of dust-generating winds over the Sahel and Sahara

Abstract:

The Sahara is the world’s largest source of airborne mineral dust, which affects global climate through changes in solar and infrared radiation, ice nucleation, and their impact on albedo. Climate models struggle to correctly capture the past variability in mineral dust, and future projections of dust emission remain highly uncertain. A major source of this uncertainty is that cold pool outflows from moist convection (‘haboobs’), which are a key dust uplift mechanism in the Sahara and Sahel, are essentially missing from global models, due to their use of parameterised convection. Therefore any impacts of climate change on haboobs, and their associated dust emissions, are not captured by current climate models, raising major questions on the reliability of current projections of dust. Here we present results from the first convection-permitting simulations of pan-African climate change, which are able to explicitly capture haboobs, to determine the impact of missing haboobs in climate models on projections of dust-generating winds. Our results show that simulations with parameterised convection are unable to reproduce the observed summertime maximum in dust-generating winds, and that explicit convection is key to capturing the observed seasonal cycle. In a future climate explicit convection leads to an earlier increase in the summertime dust maximum, but this is due to indirect effects of explicit convection on the regional climate, as opposed to changes in haboobs themselves. These results highlight the need to improve the general representation of convection, not only haboobs, in order to improve dust projections.