Climate and conflict in the Eastern Pacific: exploring a possible catastrophic coastal El Niño event and its impact on ancient Peruvian societies (320-200 BCE) through an interdisciplinary approach.

ongoing

Coastal El Niño (CEN) events have affected the northern half of Peru's coast for millennia bringing very warm climate conditions that lead to heavy rainfall and floods. In the central Peruvian desert of Casma, the presence of numerous fortified settlements dating from around 320-200 BCE suggests that their construction occurred during a period of warfare and regional instability. However, the reasons behind this instability remain unclear. The larger of these fortresses, Chankillo, may hold the key to understand when and why these structures were built. Well-preserved wooden lintels in Chankillo’s structures provide an opportunity to study the environmental past. A preliminary tree-ring width study revealed an anomalous wide ring in timbers from the lintels just before Chankillo’s construction, which could be the result of a CEN-induced catastrophic episode of heavy rainfall. This extreme CEN may have sparked instability and warfare, shaping central Peruvian history around 2,300 years ago. PACHACUTI aims to determine whether a catastrophic CEN event took place around 320-200 BCE, before Chankillo’s construction, by combining dendroarchaeology, annually-resolved stable oxygen isotope (18O) analysis and radiocarbon wiggle-matching. This ground-breaking interdisciplinary approach will use samples from Chankillo’s architectural timbers to develop an 18O chronology capturing hydroclimate variability over the 120 years before Chankillo’s construction. This novel record will encapsulate the frequency, magnitude and impacts of past CEN events during this period, offering insights into the climatic context surrounding Chankillo’s origins. Furthermore, it will also serve to date other archaeological sites in the region. If proven, this discovery will reveal the oldest known CEN event with a significant societal impact, highlighting the need to improve mitigation strategies to reduce the impact of future extreme hydroclimatic events for modern societies.