Combined social and climatic factors explain the long-lasting decline of Harappa

Tiwanaku was a regionally significant, state level polity in the south-central Andes from ca. 500–1000 CE. The development of complex society in the region was greatly facilitated through intensified agricultural systems that relied on monsoonal precipitation. At the end of the first millennium CE, the Tiwanaku political regime collapsed, and their raised field systems were mostly abandoned within 200 years or less. It has been suggested that a prolonged period of aridity contributed to the collapse, but questions have remained about its chronology and severity. In this study, we investigated the relationship between δ2Hwax and δ18Ocalcite values, aridity and societal change. A period of nondeposition or erosion occurred between 915 and 1025 CE indicating a low lake stand exposing the core site. This extended and pronounced drought ending 1025 CE was recorded in the isotopic proxies extracted from lake sediments that show this period of aridity persisted into the 13th century. The broad agreement between our record and other regional paleoenvironmental archives of Holocene climate variability is consistent with Northern Hemisphere oceanic and atmospheric circulation patterns as a mechanism for driving centennial scale climate change in the Andes and supports the correspondence between prolonged drought and the collapse of Tiwanaku.