A significant portion of the global population is at risk from once-in-a-century flooding, with estimates suggesting around a quarter of the world's population, or approximately 1.8 billion people, may be affected. The flooding threat appears to be a global issue, with various regions, including china and coastal communities, facing increased risks due to climate change. The exact number of people at risk and the severity of the flooding may vary, with some studies indicating that millions more could be impacted by coastal flooding in the coming decades.