Drought special part 4. End of civilizations

Ingenious water management helped the ancient Wari state expand throughout the Andes. Why couldn’t it survive a drought?

That’s the teaser for the third “feature article” of the drought series published recently in Science.

The article concerns a faction of the Wari state that successfully inhabited dry hillsides of the Moquegua Valley of southern Peru.

…dry periods certainly stressed prehistoric communities—sometimes intensely, if they tipped into regional droughts. But for Wari, they also appear to have led to innovation, including new and better ways of storing, moving, and using precious water. Their canals were far longer and sturdier than any that came before, and although some other cultures had used agricultural terraces, Wari massively scaled up the technology and brought it to new regions.

Their infrastructure included:

1. A 20 km mountain-slope canal
2. Gravel and earth terraces to retain water for slow release to agricultural lands (essentially a form of storage reservoir)
3. A brewery (where a beer made from molle berries was brewed)

Sounds like a pretty fun place—until the civilization collapsed during a severe drought.

The opening of the article seems to suggest that there’s some mystery about how a civilization replete with water infrastructure could be obliterated by drought. Some social science theories are offered. But no one seems to countenance the most simple explanation—that the water storage capacity of the terraces was insufficient to sustain supply during a severe drought, leading to collapse in food supply and ultimately the end of the city.

The article has a fascinating ending:

Ironically, Wari engineering long outlasted the state itself. Beginning in the 1300s, the expanding Inca Empire repurposed Wari canals, roads, and agricultural terraces to feed and connect their far-flung territories.