Practising historical climatology in West Africa: a climatic periodisation 1750–1800

This paper presents the first interdecadal and interannual periodisation of the climate in West Africa between 1750 and 1800. The climatic synthesis is founded on previously unexploited British documents written at Cape Coast Castle, Cape Coast, Ghana and travel journals, which are combined with previous research on the Sahel. By combining historical evidence with the most recently identified rainfall patterns in the Sahel and the Guinea coast, the climatic periodisation distinguishes between wetter and drier periods. The results show that there was great interannual and interdecadal variability in the West African rainfall regime in the 18th century. The historical evidence suggests that the climate in the Sahel and the Guinea coastal interior alternated between five wet and dry periods, whereas the coastal dry zone alternated between three wet and dry periods. The most pronounced changes in the climate are found in the 1780s and 1790s. The Guinea coastal interior and the Sahel experienced a wet period in the 1780s and a dry period in the 1790s, whereas the coastal dry zone was drier in the 1780s and wetter in the 1790s. The investigation shows that the secondary rainy season on the Gold coast was weak or non-existent.