Agriculture, Settlement, and Abrupt Climate Change: The 4.2ka BP event in Northern Mesopotamia

An abrupt aridification event at 4200 BP has been recorded in 41 paleoclimate proxies in the Old World, from Kilmanjaro, Tanzania to Rajasthan, India, East Asia and the Pacific. This event is particularly well defined for Western Asia, where it has been associated with the abandonment of settlements across the Fertile Crescent and the collapse of states on the Levantine coast and in the dry-farming plains of Northern Mesopotamia, including the Akkadian Empire. Adaptations to climate change are constrained by both local environmental and social factors. Agriculturalists, especially those living in pre-industrial societies, are particularly susceptible to changes in precipitation. The Tell Leilan Regional Survey, which systematically studied sites in a 1650km2 area of Northeastern Syria, records one set of adaptations to this event in an area where dry-farming provided the subsistence base. The survey transect crosses ecotones, from the present 500mm isohyet in the North to the 250mm isohyet in the South, and contains diverse wadi systems, ground water resources, soil profiles, and an ancient marsh/lake-- all of which allow this region to be taken as a microcosm of Northern Mesopotamia. In order to contextualize our study of human response to abrupt climate change, it is necessary to consider how the economic and social systems that were previously in place were transformed by this event. This study attempts to quantify climate change and model its effects on agricultural, pastoral, and settlement systems in Northeastern Syria from 2400-1700 BC. From 2400-2300 BC, optimal climate conditions coincided with the consolidation of an indigenous state. The next century witnessed the Akkadian conquest and imperialization of the Habur plains, which resulted in both the intensification and extensification of agro-production. During the next 300 years, (2200-1900 BC), rainfall plummeted to 70% of the climatic optimum, triggering the abandonment of cities along with their attendant villages. The survey records an 80% decline in settled hectares from the previous period. The only agricultural villages that remained occupied during this crisis were either concentrated along perennial wadis or located in areas with ample groundwater. Otherwise, the survey recorded the presence of a few temporary sites, probably camps belonging to semi-nomadic pastoralists, a lifestyle which may have begun in response to this event. The precipitation regime stabilized at approximately 1900 BC, allowing for a massive resettlement of the area. This resettlement did not, however, lead to a resumption of third millennium agricultural practices; instead, these villages embraced a flexible economic regime, which emphasized a reliance on pastoral as well as agricultural products, and as such, was well-adapted to the more marginal conditions of the early second millennium BC. This paper, therefore, attempts to quantify the effects of the 4.2 ka BP abrupt climate change event on ancient agricultural systems, settlement patterns, and societies through archaeological survey in northern Mesopotamia.