Ground data confirm warming and drying are at a critical level for forest survival in western equatorial Africa
- Published
- Accepted
- Subject Areas
- Coupled Natural and Human Systems, Biosphere Interactions, Climate Change Biology
- Keywords
- Climate change, Tropical forests, Central Africa, Gabon, Lopé, Warming, Drying, Seasonality, Meteorology, Western equatorial Africa
- Copyright
- © 2019 Bush et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2019. Ground data confirm warming and drying are at a critical level for forest survival in western equatorial Africa. PeerJ Preprints 7:e27848v1 https://doi.org/10.7287/peerj.preprints.27848v1
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 2000mm total annual rainfall. Meteorological data for Central Africa are notoriously sparse and incomplete and there are substantial issues with satellite-derived data because of inability to ground-truth estimates and persistent cloudiness. 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 in equatorial Africa 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 western equatorial Africa. We used 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 light-deficient, cool, long dry season. Long-term climatic means have changed significantly over the last three decades, with warming occurring at a rate of 0.23°C per decade (minimum daily temperature) and drying at a rate of 50mm per decade (total annual rainfall). Inter-annual variability is highly influenced by sea surface temperatures of the major oceans. In El Niño years Lopé experiences both higher temperatures and less rainfall with increased contrast between wet and dry seasons. Lopé rainfall observations lend support for the role of the Atlantic cold tongue in “dry” models of climate change in the region.
Conclusions. Dry season cloud in western equatorial Africa plays a key role in reducing evaporative demand during seasonal drought and maintaining evergreen tropical forests despite relatively low annual rainfall. In the context of a rapidly warming and drying climate, urgent research is needed into the sensitivity of clouds to ocean temperatures and the viability of humid forests in this dry region should the clouds disappear.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Fourier spectra for weather data from Lopé NP, Gabon
Fourier spectra represent the power of the cycle at each possible frequency. Peaks in the spectra indicate dominant cycles in the data. The dotted vertical lines indicate the position of annual (1/12 = 0.083 cycles per month) and biannual (1/6 = 0.167) cycles. Time series were standardised but observation lengths differ.
Seasonality of aerosol optical depth at Lopé NP, Gabon (2014-2017)
Lines indicate the monthly means calculated from daily data. The three wavelengths (440nm, 500nm and 675nm) are all relevant for photosynthetically active radiation.
Matrix of Pearson correlation coefficients for four oceanic indices and rainfall at Lopé NP, Gabon
Red indicates negative correlation and blue indicates negative correlation. The tint indicates the strength of the correlation.
Matrix of Pearson correlation coefficients for four oceanic indices and minimum temperature at Lopé NP, Gabon
Red indicates negative correlation and blue indicates negative correlation. The tint indicates the strength of the correlation.