The great drought of 563–594 and the crisis of the Moche

In 1983 two cores were drilled through the Quelccaya ice cap in the southern highlands of Peru; their visible annual layers gave a record of precipitation for the past 1,500 years. In 1991 Izumi Shimada, Crystal Barker Schaaf, Lonnie Thompson and Ellen Mosley-Thompson drew attention to one anomaly: a drought that began abruptly around 563 and lasted until about 594, with precipitation some 30 per cent below the mean — remarkable in the whole record for its severity, abrupt onset and persistence. Shorter droughts occurred in 524–540 and 636–645, and a wet period followed in 602–635; for this part of the cores the dating is accurate to about ±20 years. Since the rivers of the desert coast are fed by rain in the highlands, the authors argued that the drought sharply reduced the water available for irrigation.

The Moche IV–V transition, which archaeologists date to about 550–600, fits this picture. Late in Moche IV a great flash flood damaged the base of the Huaca del Sol at the southern capital, and sand dunes then invaded the site and cut off its irrigation canals; the capital was abandoned, and the Moche seem to have lost control of their lands south of the Moche valley. In Moche V power moved inland and northward, to new towns at the necks of the valleys — Galindo in the Moche valley and Pampa Grande in the Lambayeque valley, a city of perhaps 10,000–15,000 people — with large storehouses and a firm grip on the intakes of the main canals.

The interpretation remains debated. The English Wikipedia summarises the ice-core evidence differently: climatic events of 563–594, possibly a ‘super El Niño’, brought thirty years of intense rain and flooding followed by thirty years of drought, in the aftermath of the climatic downturn of 535–536; the Russian article speaks of some thirty years of El Niño rains followed by a long drought. Shimada and his colleagues found no concrete evidence for the older theory of a Wari invasion and saw the late-6th-century drought as the trigger of changes prepared by earlier droughts and El Niño floods. Moche polities survived in some valleys after 650, with fortified settlements suggesting conflict over scarce resources.