Early urbanism in Mesopotamia coincided with increased moisture between 6500 to 5500 years BP

Climate change is thought to have played a significant role in the rise and demise of complex Mesopotamian societies throughout the mid- to late Holocene. However, assessing the links between societal change and climate variability has been historically challenging, in part due to an absence of long-term, well-dated palaeoclimate archives located in close proximity to key archaeological sites. Here, we synthesise proxy data with archaeological information from Mesopotamia to demonstrate that the earliest urban development documented in this region coincides with increasing and potentially peak effective moisture in the mid-Holocene by $\sim$5500 BP. We posit that increasing moisture availability likely facilitated the expansion and development of the earliest cities, with resource extraction under favourable climatic conditions providing new opportunities for urban centres to expand their resource areas into new domains, and far beyond what is evident in earlier periods. Following $\sim$5200 BP, these same archives show increasing aridity coincident with the end of the Late Chalcolithic, and abandonment of several key settlements. Taken together, our work contextualises the evolution of critical urban centres in Mesopotamia between 6500 to 5500 yrs BP, and underscores the sensitivity of these centres to climatological variability.