Why is Xi Jinping building secret commodity stockpiles?

From The Economist

Over the past two decades China has devoured enormous amounts of raw materials. Its population has grown bigger and richer, requiring more dairy, grain and meat. Its giant industries have been ravenous for energy and metals. In recent years, though, the economy has suffered from political mismanagement and a property crisis. Chinese officials are adamant that they want to shift away from resource-intensive industries. Logic dictates that the country’s appetite for commodities should be shrinking, and shrinking fast.

In reality, the opposite is happening.