“Late-stage” deforestation enhances storm trends in coastal West Africa

Taylor, Christopher M. ORCID: https://orcid.org/0000-0002-0120-3198; Klein, Cornelia ORCID: https://orcid.org/0000-0001-6686-0458; Parker, Douglas J.; Gerard, France ORCID: https://orcid.org/0000-0001-5916-5174; Semeena, Valiyaveetil Shamsudheen ORCID: https://orcid.org/0000-0002-1895-449X; Barton, Emma J. ORCID: https://orcid.org/0000-0001-5945-9244; Harris, Bethan L. ORCID: https://orcid.org/0000-0002-0166-6256. 2022 “Late-stage” deforestation enhances storm trends in coastal West Africa. Proceedings of the National Academy of Sciences, 119 (2), e2109285119. 8, pp. https://doi.org/10.1073/pnas.2109285119

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Abstract/Summary

Deforestation affects local and regional hydroclimate through changes in heating and moistening of the atmosphere. In the tropics, deforestation leads to warming, but its impact on rainfall is more complex, as it depends on spatial scale and synoptic forcing. Most studies have focused on Amazonia, highlighting that forest edges locally enhance convective rainfall, whereas rainfall decreases over drier, more extensive, deforested regions. Here, we examine Southern West Africa (SWA), an example of “late-stage” deforestation, ongoing since 1900 within a 300-km coastal belt. From three decades of satellite data, we demonstrate that the upward trend in convective activity is strongly modulated by deforestation patterns. The frequency of afternoon storms is enhanced over and downstream of deforested patches on length scales from 16 to 196 km, with greater increases for larger patches. The results are consistent with the triggering of storms by mesoscale circulations due to landscape heterogeneity. Near the coast, where sea breeze convection dominates the diurnal cycle, storm frequency has doubled in deforested areas, attributable to enhanced land–sea thermal contrast. These areas include fast-growing cities such as Freetown and Monrovia, where enhanced storm frequency coincides with high vulnerability to flash flooding. The proximity of the ocean likely explains why ongoing deforestation across SWA continues to increase storminess, as it favors the impact of mesoscale dynamics over moisture availability. The coastal location of deforestation in SWA is typical of many tropical deforestation hotspots, and the processes highlighted here are likely to be of wider global relevance.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1073/pnas.2109285119
UKCEH and CEH Sections/Science Areas:	Hydro-climate Risks (Science Area 2017-)
ISSN:	0027-8424
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	deforestation, West Africa, convective storms, rainfall, sea breeze
NORA Subject Terms:	Hydrology Meteorology and Climatology Atmospheric Sciences
Date made live:	06 Jan 2022 16:41 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/531401

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