Journal des sciences de la Terre et du changement climatique

Abstrait

Impacts of Climate Change on Rainfall Amount, Onset and Length of Rainy Season over West Africa

Elijah Adesanya ADEFISAN

Onset, cessation and hence length of rainy season as well as the annual and seasonal amount of rainfall were investigated for a possible climate change impacts in the near future using ensembles of eight regional climate models (RCMs). Comparison of the model ensembles with global precipitation climatology project (GPCP) data shows a good agreement with the observation. Apart from the onset of rainfall and annual amount with error of 51%, 16.5% respectively over Guinea zone, the percentage error for all other parameters were found to be just 10% or less over the zones and in the West African sub-region. Analysis of the present (1997-2007) and its different from the near future (2027-2037) with IPCC scenario A1B shows some reductions (or early) and increment (or delay) in some of these rainfall characteristics. These changes were investigated in each of the three climatic zones and also the entire West Africa. Rainfall amount was found to be reduced to 0.29mm/day (7.9%) over the entire subregion while this reduction is more pronounced in the Sahel (with 0.37mm/day) than the other two zones. Throughout the three zones and of course the entire West African sub-region, there is general delay of onset, early cessation and therefore shorter length of rainy season. Over Guinea, length of rainy season was reduced by 27 days while it was 14 and 13 days respectively over Savana and Sahel, the mean over West Africa is 18 days. This threatens the agricultural practices and therefore calls for a way of getting plant species that mature and germinate early enough so at to mitigate the impacts of shorter length of rainy season in the near future over West Africa. Though, there seems to be a relief in the rainfall amount from June to September over Guinea as there is an increase of 1.63mm/day (25%), but this poses some threats in terms of damages and destruction to lives and properties that may be associated with frequent occurrences of floods and probably squall lines. Savana has little reduction of 0.3mm/day while the reduction is a bit high over Sahel with 1.0mm/ day, this threatens agricultural practices and water resources management over these zones as the rainfall amount over them presently is not substantial enough for a sustainable agricultural practice.