Abstract
The Congo Basin is one of three key areas of tropical convection and contains the planet’s second largest rainforest. Understanding how global warming might change its climate is crucial, particularly during the dry seasons, when rainfall amounts currently bring the rainforest boundaries close to the threshold of viability. There is considerable uncertainty in projections of future rainfall change from the Coupled Model Intercomparison Project (CMIP5) under the high-emissions experiment (RCP8.5). Whilst there is a general trend towards wetting in most months, its magnitude varies considerably. In the December to February dry season, the projected change in seasonal rainfall varies from 2 to 160 mm across models. This study uses a regionally-focused process-based assessment to understand inter-model differences in rainfall projections, as a first step to assessing their plausibility. Models which produce the most wetting by the end of the century feature enhanced convection over the Congo Basin region, enhanced subsidence in the African subtropics, and decreased uplift over the Maritime Continent. In contrast, models with a small wetting response feature reduced convection over the Congo Basin. This indicates that wetting over the Congo Basin is related to a weakening of the Indian Ocean Walker circulation, reminiscent of a positive Indian Ocean Dipole state. Models with the highest magnitude wetting also feature greater low-to-mid-level moisture flux from the north and the east compared to models with less wetting. These results indicate that the future degree of wetting over the Congo Basin will be linked to changes in convection over the Maritime Continent.
Highlights
The Congo Basin hosts the planet’s second largest rainforest, a vital global carbon store and significant element of the global carbon cycle
To assess the likely rainfall changes in this season, we focus on a smaller domain than in previous figures (10°E–35°E, 10°S–5°N, green box in Fig. 4), which comprises the core of the tropical rain-belt over the Congo Basin during this season
Values of ΔP are small compared to the large range of model climatological values; in January, for example, the mean historical rainfall in models ranges from 28.1 mm to 165.0 mm month− 1, whereas the ΔP values only range from − 4.0 to 43.5 mm month− 1
Summary
The Congo Basin hosts the planet’s second largest rainforest, a vital global carbon store and significant element of the global carbon cycle. A shift in the location or intensity of rainfall in the dry seasons in the future is likely to have implications for the rainforest extent, which in turn is likely to influence the carbon storage capacities of the region (James et al 2013; Malhi et al 2013) These changes are likely to occur concurrently with increasing rates of deforestation in the region, which some studies have found to result in drier and warmer conditions in parts of the Congo Basin, by affecting evapotranspiration, cloud physics and moisture circulation patterns (Maynard and Royer 2004; Werth and Avissar 2005; Bala et al 2007; Akkermans et al 2014; Bell et al 2015). This approach will be a vital first step towards providing reliable projections of future change in the region
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