Urban Development and Water Environment Changes in Asian Megacities

Abstract

Since their growth into modern cities, Asian megacities have seen a change in their water environment due to such undertakings as the reclamation of their regional streams, rivers, lakes and ponds, and commencement of large-scale groundwater withdrawal projects. As a result, so-called water environment issues emerged in many megacities. A time-series analysis of the process of their emergence reveals that the earlier a city developed, the earlier water environment issues emerged. Accordingly, one can well expect that a city that is currently demonstrating remarkable growth might see in the near future an emergence of water environment issues similar to those in other cities that developed in earlier days. In this research, the urban development processes in the Asian megacities and resulting changes in their water environment were discussed, and the water environment issues that have emerged as a consequence were sorted out. As a result, it has been brought to light that the cities that developed early also saw water environment issues emerge early, but a good part of them are now in the process of being solved. This research stopped short of examining any specific actions taken to address those issues, but a remaining challenge is to apply in an effective fashion the approaches and experience of those cities to other megacities. As a city develops, changes occur to its water environment, such as a decrease in the area of its waters. Such changes would result in reduced groundwater recharge or might also diminish water retention and other functions served by the surface ground, possibly making it vulnerable to floods. It is a very important task to assess what changes in water environment lead to water environment issues to what extent, but there is still very little understanding of these questions. Presumably, a challenge remains for us to answer them in the future by studying a particular megacity.