3. Climate Change over West Africa: Recent Trends and Future Projections

The West African climate has evolved in recent decades to respond to elevated anthropogenic greenhouse gas (GHG) forcing. An assessment of its recent trends and future changes is presented here based on various data sources (observations and models), along with an extensive review of recent literature including the latest Intergovernmental Panel on Climate Change report. A gradual warming spatially variable reaching 0.5 °C per decade in recent years is observed. In addition, the Sahel has recovered from the previous drought episodes (i.e., 1970s and 1980s); however, the precipitation amount is not at the level of the pre-drought period. Although these features are common across the different data sources, their magnitudes differ from one source to the other due to a lack of reliable observation systems. Projected climate change indicates continuous and stronger warming (1.5–6.5 °C) and a wider range of precipitation uncertainty (roughly between −30 and 30 %) larger in the Sahel and increasing in the farther future. However, the spatial distribution unveils significant precipitation decrease confined to the westernmost Sahel and becoming greater and more extensive in the high level GHG forcing scenario by the end of the 21st century. This coexists with a substantial increase in both dry spell length and extreme precipitation intensity. West Sahel is thus the most sensitive region to anthropogenic climate change. The rest of West Africa also experiences more intense extremes in future climate but to a lesser extent. It is also reported from other previous studies that the projected rainy season and the growing season will become shorter while the torrid, arid and semi-arid climate conditions will substantially extend. It is thus evident that in a “business as usual” World, most countries in West Africa will have to cope with shorter rainy seasons, generalized torrid, arid and semi-arid conditions, longer dry spells and more intense extreme precipitations. Such conditions can produce significant stresses on agricultural activities, water resources management, ecosystem services and urban areas planning. However, some GHG mitigation (i.e., a mid-level forcing) could help to reduce the stress.