Michael Gagan, Linda K. Ayliffe, Nick Scroxton, Wahyoe Hantoro, Mika R. Puspaningrum, Gerrit D. van den Berg, Heather Scott-Gagan, Scott A. Condie, Larry Edwards, Hai Cheng, Jian-xin Zhao, John Charles Hellstrom, Alena K Kimbrough, Matthew J. Gagan, Bambang W Suwargadi, Joan A. Cowley, Bronwyn C. Dixon, Garry K. Smith, Neil Anderson, Henri Wong, Hamdi Rifai

The cause of the disappearance of the primitive hominin, Homo floresiensis, from the Indonesian island of Flores ~50,000 years ago is a key question in palaeoanthropology. The potential roles of human agency and climate change continue to be debated, but the history of freshwater availability critical to survival at the type locality, Liang Bua, remains unknown. Although speleothem 18O is used widely as a proxy for monsoon rainfall, seasonal rainfall variations with contrasting 18O values can distort the record without altering mean annual rainfall. Here, we reconstruct summer and winter rainfall concurrent with H. floresiensis by combining speleothem Mg/Ca (a local rainfall proxy) with 18O (for rainfall seasonality). Geochemical modelling of the Mg-18O system shows that H. floresiensis and its primary prey, Stegodon, experienced a protracted decline in mean annual rainfall from ~1,560 to 960 mm between 76,000 and 55,000 years ago. During the final occupation phase at Liang Bua 60,000–50,000 years ago, summer rainfall dropped to a record low of ~430 mm, indicative of limited recharge of river-bed watering points and dry-season water stress. These findings point to landscape aridification, and intensified human-faunal interaction around dwindling resources, as likely contributors to the abandonment of Liang Bua.