About one in six Japanese live in low-lying areas that are likely to be devastated in the event of a tsunami, underscoring the pressing need for reinforcing measures to prepare for the next big disaster, according to a study.
About one in six Japanese live in low-lying areas that are likely to be devastated in the event of a tsunami, underscoring the pressing need for reinforcing measures to prepare for the next big disaster, according to a study.
The study, by Nagoya University’s Disaster Mitigation Research Center, showed that of the nation’s 128 million residents, 21.8 million lived on land less than 5 meters above sea level, most of which extends along coastal areas.
The finding means that 17 percent of the population live in areas accounting for only 3.3 percent of Japan's total land mass.
The expected height of a tsunami and the scope of damage would depend on the topography of each area and how prepared local communities were for dealing with a disaster with countermeasures such as a seawall, researchers say.
But Nobuo Fukuwa, professor of environmental and safety management at the center who led the study, said authorities should compile response measures by taking into account various dangers facing lowlands.
“Low-lying lands are at risk not only for tsunami, but also for tidal waves, the strong tremors of a quake and liquefaction,” he said.
Fukuwa conducted the study with Kumiko Wakita and other researchers. Their findings are based on the maps showing the elevation in each of the 250-square meter segments compiled by the Geospatial Information Authority of Japan and the 2005 national census.
Tokyo had the largest number of residents living in a potentially vulnerable area, with 3.43 million, followed by Osaka Prefecture with 3.06 million, Aichi Prefecture with 1.74 million and Chiba Prefecture with 1.44 million.
The coastal region stretching from eastern Japan to Kyushu along the Pacific could be hit by tsunami generated by a massive earthquake along the Nankai Trough southwest of Tokyo.
In the area where tsunami more than 20 meters high may be generated under the government’s projection, 490,000 lived in land less than 5 meters above the sea in Shizuoka Prefecture.
The number totaled 380,000 in Mie Prefecture and 140,000 in Kochi Prefecture.
The region along the Sea of Japan also faces risks, where a major tremor could be triggered by under-sea subduction zones or offshore active faults.
In Niigata Prefecture, 630,000 lived in such lowlands, while 250,000 could be impacted in Ishikawa Prefecture.
The corresponding number stood at 1.03 million in Fukuoka Prefecture.
The study also showed that 2.63 million lived on land at even greater risk, less than 1 meter above the sea.
Of these, Tokyo, Nagoya and Osaka combined represented more than 76 percent.
Fourteen million lived in areas at 5 meters or above sea level and less than 10 meters, while 32 million resided in areas at 10 meters or above and less than 30 meters.
Tokyo, as well as Aichi and Osaka prefectures, face increased risks due to the concentration of their populations in low-lying coastal areas, with 20-30 percent of residents living on land less than 5 meters above sea level.
An average 7 percent of the population lived in lowlands less than 5 meters above the sea in the prefectures of Iwate, Miyagi and Fukushima, where tsunami struck after the magnitude-9.0 Great East Japan Earthquake on March 11, 2011.
Despite the lesser population density, tsunami caused a large number of deaths in the region.