Water, mass and atmospheric cycle occurs dynamically interacting with variety of human activities in coastal megacities of Asian regions. The coastal megacities discharge a lot of load into the sea, and concurrently these regions have a potential of purification under the balance between nature and humanity. This session will discuss the issues and the future capability of water-atmosphere-human system in the coastal megacities from the various view points of hydrology, water resources, meteorology, environmental sciences, geochemistry and geography.