What drives the intensification of mesoscale convective systems over the West African Sahel under climate change?

Fitzpatrick, Rory G.J.; Parker, Douglas J.; Marsham, John H.; Rowell, David P.; Guichard, Francoise M.; Taylor, Chris M. ORCID: https://orcid.org/0000-0002-0120-3198; Cook, Kerry H.; Vizy, Edward K.; Jackson, Lawrence S.; Finney, Declan; Crook, Julia; Stratton, Rachel; Tucker, Simon. 2020 What drives the intensification of mesoscale convective systems over the West African Sahel under climate change? Journal of Climate, 33 (8). 3151-3172. https://doi.org/10.1175/JCLI-D-19-0380.1

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Abstract/Summary

Extreme rainfall is expected to increase under climate change, carrying potential socioeconomic risks. However, the magnitude of increase is uncertain. Over recent decades, extreme storms over the West African Sahel have increased in frequency, with increased vertical wind shear shown to be a cause. Drier midlevels, stronger cold pools, and increased storm organization have also been observed. Global models do not capture the potential effects of lower- to midtropospheric wind shear or cold pools on storm organization since they parameterize convection. Here we use the first convection-permitting simulations of African climate change to understand how changes in thermodynamics and storm dynamics affect future extreme Sahelian rainfall. The model, which simulates warming associated with representative concentration pathway 8.5 (RCP8.5) until the end of the twenty-first century, projects a 28% increase of the extreme rain rate of MCSs. The Sahel moisture change on average follows Clausius–Clapeyron scaling, but has regional heterogeneity. Rain rates scale with the product of time-of-storm total column water (TCW) and in-storm vertical velocity. Additionally, prestorm wind shear and convective available potential energy both modulate in-storm vertical velocity. Although wind shear affects cloud-top temperatures within our model, it has no direct correlation with precipitation rates. In our model, projected future increase in TCW is the primary explanation for increased rain rates. Finally, although colder cold pools are modeled in the future climate, we see no significant change in near-surface winds, highlighting avenues for future research on convection-permitting modeling of storm dynamics.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1175/JCLI-D-19-0380.1
UKCEH and CEH Sections/Science Areas:	Hydro-climate Risks (Science Area 2017-)
ISSN:	0894-8755
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	Africa, convection, wind shear, precipitation, climate change, climate models
NORA Subject Terms:	Meteorology and Climatology
Date made live:	05 May 2020 22:02 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/527101

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