To your last point: the infrastructure in place along the Yangtze that enables all of those people to live so close to the river, did not exist prior to twenty

To your last point: the infrastructure in place along the Yangtze that enables all of those people to live so close to the river, did not exist prior to twenty years ago. For a useful comparison, the central valley in California would flood regularly and very destructively without modem infrastructure. Entire towns were wiped out (Google it, thousands dead in the 1800s)