Is climate the main driver of Mid-Holocene settlement dynamics on the Varamin plain?

Abstract

For different areas throughout West Asia and the Middle East, settlement discontinuities and periods of cultural decline in the Mid-Holocene have been attested. Whether these phenomena were caused mainly by climatic factors, especially periods of drought, has been an ongoing scientific debate of the last decade(s).  One of these regions, the Varamin plain, is located few kilometers east of Teheran on an alluvial fan along the southern slopes of the Elburs-mountain-range (Northern Iranian Highlands). A recent archaeological survey on the Varamin plain revealed a striking absence of archaeological finds for the end of the Proto-Elamite period (Early Bronze Age) between approximately 5000 and 4100 BP that has been interpreted as a (temporal) abandonment of the plain. This crisis presumably lasted until the beginning of the Iron Age around 3500 BP.Since paleoenvironmental and paleoclimatic information for this region are scarce, this study makes use of 3 different approaches to unravel the Holocene climate variability in West Asia in general and the Northern Iranian plateau specifically: a) analysis of climate reconstructions, b) a high-resolution snapshot simulation performed in ICON-NWP for the mid-Holocene time-slice (7000 BP) and c) a transient simulation performed with the Max Planck Institute Earth System Model (MPI-ESM) spanning the period from 8000 BP to pre-industrial (PI, 100 BP).The comparison of the regional proxy-based climate reconstructions reveals a considerable degree of hetegorenity, impeding any straightforward inferences regarding possible paleoclimatic forcings for settlement dynamics. In particular, no specific drought period can be identified that coincides with the settlement crisis.The model results show that there is a general aridification trend between 7000 BP and PI in West Asia. While absolute annual mean precipitation changes are small, the model data reveal a shift in seasonality of precipitation with drier autumns and winters but substantially wetter conditions during spring during mid-Holocene times. In combination with longer and colder winters during the Mid-Holocene, this may have enhanced water availability and therefore favored agricultural production.  Superimposed on this minor aridification trend, the model shows pronounced climatic variability with distinct multi-decadal wet and dry periods with variations of up to +/-12% in precipitation. Therefore, we cannot exclude that climatic events and variability including their geomorphological responses may have played a role in settlement discontinuties, but we can not clearly identify climate changes as the main driver.