Rare ground data confirm significant warming and drying in western equatorial Africa

Emma R Bush; Kathryn Jeffery; Nils Bunnefeld; Caroline Tutin; Ruth Musgrave; Ghislain Moussavou; Vianet Mihindou; Yadvinder Malhi; David Lehmann; Josué Edzang Ndong; Loïc Makaga; Katharine Abernethy

doi:10.7717/peerj.8732

Rare ground data confirm significant warming and drying in western equatorial Africa

PeerJ. 2020 Apr 14:8:e8732. doi: 10.7717/peerj.8732. eCollection 2020.

Authors

Emma R Bush¹, Kathryn Jeffery^{1

2}, Nils Bunnefeld¹, Caroline Tutin¹, Ruth Musgrave³, Ghislain Moussavou⁴, Vianet Mihindou^{2

5}, Yadvinder Malhi⁶, David Lehmann^{1

2}, Josué Edzang Ndong², Loïc Makaga², Katharine Abernethy^{1

7}

Affiliations

¹ Faculty of Natural Sciences, University of Stirling, Stirling, UK.
² Agence Nationale des Parcs Nationaux (ANPN), Libreville, Gabon.
³ Elephant Protection Initiative, London, UK.
⁴ Agence Gabonaise d'Études et d'Observation Spatiale (AGEOS), Libreville, Gabon.
⁵ Ministère des Eaux et Forêts, Charge de l'Environnement et du Développement Durable, Libreville, Gabon.
⁶ Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK.
⁷ Institut de Recherche en Écologie Tropicale, CENAREST, Libreville, Gabon.

Abstract

Background: The humid tropical forests of Central Africa influence weather worldwide and play a major role in the global carbon cycle. However, they are also an ecological anomaly, with evergreen forests dominating the western equatorial region despite less than 2,000 mm total annual rainfall. Meteorological data for Central Africa are notoriously sparse and incomplete and there are substantial issues with satellite-derived data because of persistent cloudiness and inability to ground-truth estimates. Long-term climate observations are urgently needed to verify regional climate and vegetation models, shed light on the mechanisms that drive climatic variability and assess the viability of evergreen forests under future climate scenarios.

Methods: We have the rare opportunity to analyse a 34 year dataset of rainfall and temperature (and shorter periods of absolute humidity, wind speed, solar radiation and aerosol optical depth) from Lopé National Park, a long-term ecological research site in Gabon, western equatorial Africa. We used (generalized) linear mixed models and spectral analyses to assess seasonal and inter-annual variation, long-term trends and oceanic influences on local weather patterns.

Results: Lopé's weather is characterised by a cool, light-deficient, long dry season. Long-term climatic means have changed significantly over the last 34 years, with warming occurring at a rate of +0.25 °C per decade (minimum daily temperature) and drying at a rate of -75 mm per decade (total annual rainfall). Inter-annual climatic variability at Lopé is highly influenced by global weather patterns. Sea surface temperatures of the Pacific and Atlantic oceans have strong coherence with Lopé temperature and rainfall on multi-annual scales.

Conclusions: The Lopé long-term weather record has not previously been made public and is of high value in such a data poor region. Our results support regional analyses of climatic seasonality, long-term warming and the influences of the oceans on temperature and rainfall variability. However, warming has occurred more rapidly than the regional products suggest and while there remains much uncertainty in the wider region, rainfall has declined over the last three decades at Lopé. The association between rainfall and the Atlantic cold tongue at Lopé lends some support for the 'dry' models of climate change for the region. In the context of a rapidly warming and drying climate, urgent research is needed into the sensitivity of dry season clouds to ocean temperatures and the viability of humid evergreen forests in this dry region should the clouds disappear.

Keywords: Central Africa; Climate change; Drying; Gabon; Lopé; Meteorology; Seasonality; Tropical forests; Warming; Western equatorial Africa.

Grants and funding

Weather data collection at SEGC, Lopé National Park, was funded by the International Centre for Medical Research in Franceville (CIRMF; 1986–2010) and by Gabon’s National Parks Agency (ANPN; 2010–present) as the institutions responsible for day-to-day running of the field station during those periods. Emma Bush received funding from a Collaborative Impact Studentship co-funded by the University of Stirling and ANPN from 2013 to 2018 to prepare and analyse these data. Nils Bunnefeld received funding from the European Research Council under the European Union’s H2020/ERC grant agreement no 679651 (ConFooBio). Yadvinder Malhi received funding from the UK Natural Environment Research Council (NE/1014705/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.