Prolonged drought on Rapa Nui during the decline of megalithic monument construction

Beginning in the 13th century, Polynesian settlers on the island of Rapa Nui engaged in megalithic monument construction, crafting hundreds of ahu platforms and moai statues from volcanic bedrock. The decline of this tradition centuries later, coincident with land-use changes and the emergence of new ritual practices on the island, has intrigued archaeologists for decades. Here, we present evidence for a transition to persistent drought conditions on Rapa Nui beginning in the mid 16th century, based on two independent reconstructions of hydrogen isotopes in rainfall inferred from hydrogen isotopes of leaf waxes preserved in wetland sediments. Consistent with observational data and model simulations, we interpret more negative hydrogen isotopes in precipitation to reflect an increase in the frequency of large storms and total rainfall amount over Rapa Nui. We show that 16th–17th century changes in human geography on Rapa Nui coincided with a sustained, multi-century decrease in annual precipitation of ~600–800 mm, which is of greater magnitude than the drying observed in recent decades. Changes in the human geography of Rapa Nui, Easter Island, Chile, in the 16th and 17th centuries and the decline in monument construction coincided with a sustained decrease in annual precipitation of approximately 600–800 millimeters, according to hydrogen isotope data from leaf waxes in sediments.