Atmosphere

The

Haute Vallée de l’Ouémé

(HVO) in Benin is located in a tropical wet and dry sub-humid climate, whereas the Drâa catchment is situated in the mostly semiarid subtropical climate zone of North Africa (see sect. I-3.4). In this chapter, the major meteorological processes including their seasonal cycles are described, which determine the weather and climate of Benin and Morocco. A better understanding of the dynamics of rainfall-bearing weather systems and how they are impacted by large-scale forcing mechanisms - such as the North Atlantic Oscillation (NAO), the El Niño-Southern Oscillation (ENSO), sea surface temperatures (SSTs) of tropical oceans, atmospheric aerosols, or land surface conditions - are instrumental in explaining and modeling rainfall variability at temporal scales ranging from days to decades. To approach this goal, meteorological research within IMPETUS has focused on identifying different types of rainfall systems in Benin and quantifying their contribution to annual rainfall. This has been complemented by studies that have tried to determine the percentage of variance in long-term rainfall fluctuations which is attributable to external factors such as SSTs, aerosols, and greenhouse gases.