More people in Japan are living in areas with potential risks of flooding compared with two decades ago due to residential development on suburban fields, a study showed Monday.
The figure stood at around 35.4 million in 2015, up 4.4 percent from 1995, according to research by Yasunori Hada, an associate professor of regional disaster prevention at the University of Yamanashi in Yamanashi Prefecture.
The number of households in areas designated as flood-prone by central and local governments soared 24.9 percent, to about 15.3 million, in the same period, according to the study that was based on flooding hazard maps for fiscal 2011 and the national census, conducted every five years.
Hada pointed to a notable increase in the number of people and households in suburban areas at risk from flooding despite the overall population decrease in Japan, because land and homes are cheaper there than in central city areas.
“In many cases, land previously deemed unlivable or not useful as rice or vegetable fields has been developed,” said Hada.
The hazard maps compiled by municipal governments and flood-prone areas have been released online.
Flooding estimates by local governments were almost in line with the actual damage seen in the city of Joso, in Ibaraki Prefecture, following torrential rain in 2015, and the city of Kurashiki in Okayama Prefecture, in a similar disaster in July.
The nation’s population has been on the decline since around 2010, but the number of people in flood-prone zones rose from about 33.9 million in 1995 to 34.8 million in 2005, going on to add about 1.5 million over the 20-year period through 2015.
The number of households in flood zones increased from about 12.2 million in 1995 to 13.9 million in 2005, eventually rising by about 3 million over the two decades.
By prefecture, Kanagawa logged the fastest increase in flood-prone area population at 17.4 percent, followed by Tokyo at 15.3 percent and Okayama at 12.8 percent.
“In addition to raising awareness among people already living in areas with potential flooding, we have to restrict use or development of land based on disaster risks,” said Hada.