"Shu Yu has been at the forefront of underground urban planning for decades. He spent many years studying in Japan, the home of modern subterranean development, before bringing his expertise to bear on his homeland, China.
...If we want to resolve urban problems related to population density and limited surface space, we must turn to underground development. It's a matter of 'ascending to the sky and reaching into the earth.' Today, underground space is still used primarily for disaster protection. During World War II, Paris turned abandoned caves into ammunition depots, secret outposts, and arsenals. London used subways. Now China plans to construct integrated civil-defense projects designed to prepare for military conflict and protect against natural disasters. For instance, rain from torrential downpours cannot adequately be drained through sewer systems and often produces flooding. Constructing underground rivers is a relatively easy solution to this problem, and it creates a sustainable way of dealing with rainwater."