Potential Factors Contributing To Sahel Drought
Originally it was believed that the drought in the Sahel primarily was caused by humans over-using natural resources in the region through overgrazing, deforestation and poor land management. In the late 1990s, climate model studies suggested that large scale climate changes were also triggers for the drought.
Based on Senegal river cycles, precipitation cycles of various El Sahel stations which are related to Solar(89–120 years) Wolf-Gleissberg cycles, and on relations to Nile floods and Equatorial lake levels, Yousef and Ghilly in 2000 anticipated that there is a considerable probability that drought will occur El Sahel Zone in 2005±4 years. This forecast was correct as drought occurred in El Niger in 2005 and again in 2010.
In 2002, after the phenomenon of global dimming was discovered, a CSIRO study suggested that the drought was likely caused by air pollution generated in Eurasia and North America, which changed the properties of clouds over the Atlantic ocean, disturbing the monsoons and shifting the tropical rains southwards.
In 2005, a series of climate modeling studies performed at NOAA / Geophysical Fluid Dynamics Laboratory indicated that the late 20th century Sahel drought was likely a climatic response to changing sea surface temperature patterns, and that it could be viewed as a combination of natural variability superimposed upon an anthropogenically forced regional drying trend. Using GFDL CM2.X, these climate model simulations indicated that the general late 20th century Sahel drying trend was attributable to human-induced factors; largely due to an increase in greenhouse gases and partly due to an increase in atmospheric aerosols. In IPCC future scenario A2 (CO2 value of ≈860 ppm) Sahel rainfall could be reduced by up to 25% by year 2100, according to climate models.
A 2006 study by NOAA scientists suggests that the Atlantic Multidecadal Oscillation plays a leading role. An AMO warm phase strengthens the summer rainfall over Sahel, while a cold phase reduces it. The AMO entered a warm phase in 1995 and, assuming a 70-year cycle (following peaks in ≈1880 and ≈1950), will peak around 2020. A 2009 study found further evidence for a link between the AMO and West African drought.
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