L'involution démographique et urbaine dans l'aire tokyoïte

National audienceJapan faces a brand new demographical situation. Prospective studies announce a shrink of the population from 2006 on, whereas it is almost possible to say that this shrinkage has already strarted. In addition, the japanese population super aging. Prospective studies stress that within 20 years, 25% of the population should be over 60 years old. As for whole Japan, Tokyo metropolitan area has to face the same demographical situation. These transformations have important direct consequences on the urban form, and can be classified in two types.The first type of transformation that will be considered in this paper concerns suburban shrinking processes. Tokyo's suburb mostly spread from the 1960's on, when baby-boomers started working. This huge suburban growth remained until the 1980's, during the flying economy time, that encourged families to settle away from Tokyo center to access to individual housing. It is in this frame that new towns such as Tama New Town (Tokyo-To), Koshigaya (Saitama Prefecture) ou Kashiwa (Chiba Prefecture) were developed. But these cities are nowadays problematically abandonned. Formerly thought for couples with children, they don't correspond any more to the aging population that lives in, especially concerning comfort ans accessibility. Consequently, brownfields and “ghost areas” are developping in new towns.The second type of transformation that will be considered concerns intra urban dynamics. The japanese urban model is changing. On the contrary to the occidental cliché, and despite the high density of its population, Tokyo has been a low city until recently, and has a considerable development potential. According to Architect Livio Sacchi studies, 52% of the whole space is used. So the current vertical densification (rising Tokyo) makes a rupture with the traditionnal japanese urban model. But it is also a way to answer the aging population demands.Thus, brand new planning issues are raising: what response can be given to the needs of a super aging urban society? How can shrinking processes be stopped or solved? Such questions may constitute the chore of urban planning politics.Le viellissement et la diminution de la population à Tokyo conduisent à une ville moins diluée dans l'espace par un double phénomène de rétraction périurbaine d'une part et de retour au centre d'autre part. Cette situation sans précédent soulève des questions majeures d'aménagement urbain