Abstract
The summertime Sahara and Sahel are the world’s largest source of airborne mineral dust. Cold-pool outflows from moist convection (‘haboobs’) are a dominant source of summertime uplift but are essentially missing in global models, raising major questions on the reliability of climate projections of dust and dust impacts. Here we use convection-permitting simulations of pan-African climate change, which explicitly capture haboobs, to investigate whether this key limitation of global models affects projections. We show that explicit convection is key to capturing the observed summertime maximum of dust-generating winds, which is missed with parameterised convection. Despite this, future climate changes in dust-generating winds are more sensitive to the effects of explicit convection on the wider meteorology than they are to the haboobs themselves, with model differences in the change in dust-generating winds reaching 60% of current values. The results therefore show the importance of improving convection in climate models for dust projections.
Highlights
Airborne mineral dust affects solar and infrared radiation[1,2], nucleates ice in clouds[3], darkens snow and ice surfaces when deposited there[4] and is a health hazard[5]
For the Sahara and Sahel, dust uplift is dominated by the daytime breakdown of the nocturnal low-level jet (LLJ) as well as, in the summer, haboobs generated from convective storms
Model setups are detailed in Methods, but key to interpretation here is that the explicit convection improves the entire West African monsoon[26], as well as the intensity of storms within it[23]
Summary
Airborne mineral dust affects solar and infrared radiation[1,2], nucleates ice in clouds[3], darkens snow and ice surfaces when deposited there[4] and is a health hazard[5]. Fifth Assessment Report of the Intergovernmental Panel on Climate Change has shown that they fail to capture basic features of Earth’s dust cycle and past inter-annual variability[8] Such failures of dust models are due to a combination of the difficulty in representing the land surface[9,10], wet and dry deposition[11], the dust size distribution and radiative properties[11] and the rare highwind events that dominate dust uplift[12,13]. We build on a previous study[25], which presented future climate projections of changes in extreme rain from 4.5 km gridspacing regional simulations of African climate (‘CP4’), alongside an equivalent 25 km run with parameterised convection (‘P25’), to quantify the impact of explicitly capturing convection, and by association haboobs, on future climate changes in dustgenerating winds These simulations use 10 years of past climate (1997–2007, ‘CP4’ and ‘P25’), and 10 years around 2100 under a Representative Concentration Pathway (RCP) 8.5 scenario (‘CP4FC’ and ‘P25FC’). Model setups are detailed in Methods, but key to interpretation here is that the explicit convection improves the entire West African monsoon[26], as well as the intensity of storms within it[23]
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