Variations of East African Climate during the Past Two Centuries

Abstract

The evidence on the climatic history of East Africa over the past two centuries comprises historical accounts of lake levels, observations and analyses of glacier variations, wind and current observations in the Indian Ocean, as well as raingauge measurements. East Africa experiences its rainy seasons in boreal spring and autumn, centered around April–May and October–November; the spring rains being more abundant and the autumn rains more variable. Rains tend to be abundant/deficient with slow/fast westerlies (UEQ) and Eastward Equatorial Jet (EEJ) in the upper hydrosphere of the equatorial Indian Ocean. A drastic climatic dislocation took place during the last two decades of the l9th century, manifest in a drop of lake levels, onset of glacier recession, and acceleration of UEQ and EEJ. The decades immediately preceding 1880 featured high lake stands, extensive glaciation, and slow UEQ and EEJ, as compared to the 20th century. The onset of glacier recession in East Africa after 1880 contrasts with a start of ice shrinkage in New Guinea and the Ecuadorian Andes around the middle of the l9th century. The regional circulation regime characterized by slow UEQ and EEJ in the decades prior to 1880 was conducive to extensive ice cover along with high lake stands in East Africa, and this may account for the onset of glacier recession much later than in the other mountain regions of the equatorial zone. The evolution of East African climate over the first half of the l9th century merits further exploration.