Active Monsoon in West Africa and Sahel

Active Monsoon in West Africa and Sahel



10 September 2012

Many parts of West Africa and the Sahel have experienced flooding since the end of July because of a very active monsoon. This was mainly caused by interactions between the atmosphere and the ocean and above normal temperatures over the Mediterranean region. The African Centre of Meteorological Applications for Development (ACMAD) has issued a report describing these patterns, related flooding events and impacts.

ENSO (El Niño-Southern Oscillation) is among the major drivers of rainfall variability in the tropics including sub-Saharan Africa. Over the past few months, a transition from ENSO neutral to El Niño was observed in the equatorial Pacific. Such a situation contributes to the irregular distribution of West African monsoon rainfall during the season. Disruptions to the onset and withdrawal of the monsoon, and wet and dry spells have been observed during summers characterized by a transition from ENSO neutral to El Nino conditions in the Equatorial Pacific.

Much more importantly, a very active phase of the Madden Julian Oscillation (a global phenomenon that modulates convection and rainfall in the tropics at intraseasonal timescales) was observed over the region.

There were above normal temperatures over North Africa and the Mediterranean sea from May to July 2012 and beyond. An active monsoon season with rainfall recorded over desert locust prone areas of the Sahel has been reported in association with above normal temperatures in north Africa and the Mediterranean sea during spring and summer. International support is being mobilized to strengthen locust development monitoring in the Sahel this year.

From late July to Late August 2012, precipitation above 150% of normal was recorded in southeastern Mauritania and adjacent areas in Mali, Senegal, the north of Burkina Faso, the middle and lower Niger river basin in Mali, the Lake Chad basin in Niger, Nigeria and Cameroon. Flash and riverine floods due to excessive precipitation at and upstream of many locations of the Lake Chad and River Niger basin were reported.


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