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

Drought may have contributed to changes in human geography on Rapa Nui in the late 16th and early 17th centuries, but there are currently no continuous paleoclimate records that provide direct, quantitative insight into local hydroclimate conditions during this time period. Here, we present new evidence for a multicentury rainfall deficit on Rapa Nui beginning at approximately 1550 CE, based on two independent reconstructions of hydrogen isotopes in rainfall inferred from hydrogen isotopes in leaf waxes preserved in wetland sediments. Chain-length distribution data suggests that known vegetation changes on Rapa Nui (e.g., palm deforestation) did not significantly influence the sources of leaf waxes for either wetland. Therefore, we assume that leaf wax hydrogen isotopes reflect isotopes in precipitation at a constant offset through time. We use instrumental data from the Global Network of Isotopes in Precipitation (GNIP) to show that there is a significant relationship between isotopes in precipitation over Rapa Nui and mean annual rainfall amount. We then apply the relationship between these two variables to estimate the magnitude of drought at 1550 CE, inferred from our leaf wax records. We estimate that the period 1550 CE to 1720 CE on Rapa Nui saw a 600-800 millimeter decline in average annual rainfall relative to the previous three centuries. This drought is of greater magnitude than the drying observed in recent decades and likely posed significant challenges to the 16th-17th century inhabitants of Rapa Nui.