Deforestation, declining rainfall and drought in West Africa
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CTA. 1997. Deforestation, declining rainfall and drought in West Africa. Spore 69. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/48729
Since the turn of the century up to 90% of the once extensive belt of coastal rainforests in West Africa has been cleared for farming, mining and the timber industry. A new study has now revealed that this destruction of rainforests may have caused...
Since the turn of the century up to 90% of the once extensive belt of coastal rainforests in West Africa has been cleared for farming, mining and the timber industry. A new study has now revealed that this destruction of rainforests may have caused a decrease in rainfall over the last twenty years and contributed to the droughts in Mali and Niger. Rainforests are responsible for generating rain that falls downwind. More than 50% of the rain that falls on the forest canopy evaporates to form clouds that help to maintain rain that help to maintain rain fall on the drier lands in the interior. If the coastal rainforests are cut down, a greater percentage of rain falls to the ground and the water either seeps into the soil or flows directly back to the sea. Evaporation is therefore reduced and drought-prone countries further inland become more at risk from lower rainfall. Researchers from the Centre for Global Change Science at the Massachusetts Institute of Technology (MIT) have developed a statistical model to represent the hydrological cycle of the West African monsoon. The model takes into account energy flows, rainfall and evaporation in the coastal region as well as the level of condensation as new clouds form inland. It also predicts the position of the permanent weather front, which is the major source of West African coastal rainfall, known as the Inter-Tropical Convergence Zone (ITCZ). The model confirms their hypothesis that deforestation will lead to declining rainfall but, more alarmingly, predicts that the ITCZ, which normally moves across the continent during the summer monsoon season, will stay over the Atlantic Ocean. Further deforestation could lead to the forest regions being replaced by savanna. This would reduce evaporation even more and could cause the collapse of the monsoon system. Although the model is fairly crude, researchers at MIT believe that the decline in rainfall since 1970 confirms their predictions. Massachusetts Institute of Technology Centre for Global Change Science Building 54 1312 Cambridge, MA 021394307 USA
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