The surface of a rapidly urbanized city has been covered by asphalt pavements, concrete buildings, and other heat retaining structures. This coverage causes its higher temperatures even in the evening and so-called a heat island phenomenum can be found. The accumulated heat makes ambient air warmer and causes an updraft of the air, being followed by a localized torrential downpour. The materials used for these structures are usually unpearmeable and help the rain water run off quickly into sewer pipe through their surfaces.
This study places an emphases on porous asphalt mixtures that can keep the water in themselves and discharge it gradually. The effect of porous asphalt pavements preventing the flood is examined by a case study in Meguro area where an actual flood took place and wide area was covered by water.
It was found that it is very effective to employ the porous asphalt pavements to prevent this kind of flood. The void is recommended to be larger than 20%.