The development of the ancient irrigation system at Engaruka, northern Tanzania: physical and societal factors

Climate data from Empakaai Crater in northern Tanzania, covering the last 1200 years, are related to the establishment, development and decline of the ancient irrigation system at Engaruka. New dates for the system are linked to reconstructed climatic variations and historical data on long-distance and regional trade and migration patterns. A shift from a comparatively humid climate to drier conditions in the 1400s prompted the establishment of irrigated agriculture at Engaruka, and a flourishing long-distance trade increased its value as a water and food source for passing caravans. Once established, the land-use system at Engaruka was sufficiently resilient to survive and even intensify during much drier climate from c. 1500 to 1670 CE (Common Era) and during the decline of caravan trade between c. 1550 and 1750. The ancient land-use system probably reached its maximum extension during the humid conditions between 1670 and 1740, and was deserted in the early to mid 1800s, presumably as a result of the added effects of climate deterioration, the Maasai expansion, and change of livelihood strategies as agriculturalists became pastoralists. Towards the end of the 1800s irrigated agriculture was again established at Engaruka, in part driven by the transfer from pastoral to agricultural livelihoods caused by the Rinderpest.