Drought, freshwater availability and cultural resilience on Easter Island (SE Pacific) during the Little Ice Age

After decades of human-deterministic explanations for the collapse of the ancient Rapanui culture that inhabited Easter Island (Rapa Nui) before European contact (1722 CE), paleoecological studies developed over the last decade have provided sound evidence of climate changes and their potential socioecological impacts. Especially significant is the occurrence of a century-scale (1570-1720 CE) drought occurred during the Little Ice Age. Freshwater is a critical resource on Easter Island that heavily depends on rain, which maintains the only three permanent surficial freshwater sources on the island: two lakes (Rano Kao and Rano Raraku) and a marsh (Rano Aroi). Under these conditions, the LIA drought could have significantly affected human life; however, the Rapanui society remained healthy, showing remarkable resilience. There are two main hypotheses on how the ancient Rapanui could have obtained freshwater to guarantee its continuity. The intra-island migration hypothesis proposes that Rano Raraku, the cultural center of this culture, dried out and the Rapanui were forced to migrate to Rano Kao, which was likely the only surficial freshwater source during the LIA drought. This shift was accompanied by a profound cultural reorganization. The coastal groundwater hypothesis dismisses the use of lakes and other surficial freshwater sources to maintain the water-stressed Rapanui population and contends that the only routine freshwater sources during the LIA drought were the abundant and widespread coastal seeps fed by fresh/brackish groundwater. The pros and cons of these two hypotheses are discussed on the basis of the available archeological and paleoecological evidence, and it is concluded that in the present state of knowledge, neither can be rejected. Therefore, these two proposals could be complementary, rather than mutually exclusive.