The number of people living in flood zones across Japan has increased by 6.05% between 1995 and 2015, according to a survey by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). The country’s total population over that same span increased by just 1.21%. Even prefectures experiencing depopulation saw growth in the number of residents living in flood zones.

Why is this happening?

While the existing town areas suffer from ageing population, suburban sprawl has continued in areas near rivers that were once fields and rice paddies. In Kyushu, which is often hit with torrential rain and flooding during typhoon season, six prefectures (excluding Saga) have seen population growth in flood zones. In Nagasaki, the overall population has shrunk by 10.86% since 1995 while the population in flood zones grew by 10.10%. 

As of 2012, flood zones were designated based on the probability of a 200-year flood. A revision to the Flood Control Act in May 2015 saw that raised to a 1000-year flood. Although the government has spent decades developing dams and levees, residential land in flood zones has not decreased since at least the 1980s. Rather than continue spending on infrastructure projects for flood-proofing, the focus in recent years is now on convincing residents to live in safer areas. 

The Financial Services Agency has entered into discussions with home insurance providers and the Japan Housing Finance Agency to look into introducing rules that could see insurance premiums and home loan interest rates based on the relative flood risk of the property’s location. There are also calls for land-use restrictions to be introduced that would be similar to those that apply in landslide hazard zones.

Understanding flood zones

When searching for a home to buy or rent, it’s always a good idea to grab a copy of the local Hazard Maps that are often provided by the local City Hall. Some of those maps may be available to download from the city’s homepage. The maps may cover tsunami, flooding, earthquake shaking and liquefaction, landslides, and even volcanic hazards.

Source: The Nishi Nihon Shimbun, December 10, 2020.