An analysis of data from the Asahi Shimbun found that the number of people living in areas at risk of flooding when rivers overflow due to heavy rain was approximately 25.94 million people nationwide in 2020, an increase of approximately 900,000 over the past 20 years. As heavy rains become more frequent due to climate change, around 20% of the total population lives in areas at risk of flooding, and experts are calling for the need to encourage people to move to safer areas. At the end of the article, there is a national map that shows the percentage of the population in your city, town, or village that is expected to be flooded, as well as the increase or decrease in that percentage over the past 20 years. The analysis looked at approximately 3,000 of the more than 30,000 rivers across the country, mainly those with large drainage basin areas and those that cause large amounts of damage in the event of flooding, and looked at the population within areas that are expected to be flooded in the event of heavy rainfall that occurs “about once every 100 years.” The estimate was based on the “Flood Inundation Areas Expected” (2011 edition) published in the Ministry of Land, Infrastructure, Transport and Tourism’s National Land Digital Information and population data from the national census (2000-2020). According to the report, Japan’s total population has decreased by about 1.5% (approximately 1.91 million people) from 2010, when it was at its highest, over the past 20 years up to 2020, while the population of areas expected to be flooded has increased by about 3% to about 25.94 million people. Of these, the population of areas expected to be flooded by more than three meters, meaning the first floor would be submerged, was approximately 2.57 million, an increase of approximately 70,000. The population of areas flooded by more than five metres, meaning that even the second floor would be submerged, is estimated at around 260,000 people. The city with the largest population in the areas expected to be flooded is Tokyo, with approximately 4.15 million people, accounting for just under 30% of the city’s population. Approximately 920,000 people were flooded by more than three metres. This was followed by Saitama Prefecture (approximately 2.77 million people), Kanagawa Prefecture (approximately 1.7 million people), Aichi Prefecture (approximately 1.6 million people), and Hyogo Prefecture (approximately 1.4 million people), with the population increasing in 20 prefectures over the past 20 years. After the period of rapid economic growth, flood control measures such as dams led to the development of low-lying areas at risk of flooding, and as land prices were relatively cheap, population flowed in. Additionally, although some regulations have now been strengthened, the revision of the City Planning Act in 2000 also had an impact, making exceptions to urbanization control zones, where the construction of housing is generally prohibited, for areas designated by local governments through ordinances. Professor Yasunori Hata of Nihon University, who is an expert on disaster prevention, said, “Some local governments are reluctant to curb development in areas expected to be flooded due to concerns about population outflow, but with floods occurring almost every year, traditional hard countermeasures such as dams and levees are insufficient. “We need to promote land use that takes disaster risks into account, such as encouraging people to live in vacant houses in safe locations.” (Takashi Togo, Kanato Ishii) Heavy rain in Noto, 1.5 meters of flooding despite repairs after earthquake The northern part of the Noto Peninsula was hit on the 21st… (The following is a paid version, 2893 characters remaining) Asahi Shimbun, September 29, 2024, 16:00.
>>1 It is the job of municipalities to decide and regulate urban planning. This is what happens in Japan because there are so many small municipalities that they lack the ability to make proper urban planning decisions. Small municipalities should merge to gain the ability to make proper urban planning decisions.
The eastern half of Saitama was a lake bottom until the Edo period, but is now an area at zero altitude that was irrigated by diverting the Tone River.
>>10 My house is at an altitude of 80m, and the city area 1km away is at an altitude of 60m. If my house gets flooded, it will be like Japan is about to be destroyed. It’s difficult to go shopping.
>>12 You can walk to the station and use two trains, and the hazard map is white. Because it’s white, there’s no risk of flooding, landslides, soil damage, or anything else, so it’s safe. It’s convenient and safe even without a car, so the price per tsubo has always been high, and I think there’s certainly little turnover of people.
In southern Saitama, the flood limit was revised from 3 meters to 5 meters. But new detached houses (on former farmland) are being built one after another. There is also agricultural water and stingy rivers, so there is a risk of inland flooding, but do people think “my house will be fine” and aren’t they shown any hazard maps?
>>13 Even if you look at the hazard map, you’re probably overestimating it due to homeostasis bias. It should be illegal to build houses on dangerous land, or it should be mandatory to build houses on stilts.
>>15 No matter if the LDP or the Constitutional Democratic Party allocates disaster budgets, there’s no one to do it People are fleeing the construction industry The temperature at the construction site exceeds 40 degrees, and in asphalt work it exceeds 60 degrees Working outside in this heat is life-threatening, so it’s unavoidable to protect lives If they really want people to stay in the construction industry, they’ll need hourly wages of 5,000 yen and daily wages of 40,000 yen.
Detached houses in areas expected to flood should have their first floors raised and in the event of a flood risk disaster, they will have to live on the second floor or higher and reduce their belongings.
If it’s just flooding, you won’t die if you run away, so it’s fine. Well, people who live there without worrying about it don’t seem to have a sense of danger, so they’ll probably die without running away… In landslide areas, be prepared to die at any time from a little heavy rain or earthquake.
In Saitama, a new residential area was built along the Arakawa River, but after just three years the river overflowed and the area was submerged, and sadly, it was demolished again soon after. It’s called Hirakata in Ageo City.
If you don’t like the risk of natural disasters, you can’t live in Japan. Flooding is no big deal since you have time to escape. What’s really scary is the predicted tsunami from the Nankai Trough earthquake.
>>39 This time in Wajima, the peak was 121mm in an hour, and 222mm in three hours, so if we get a strong linear precipitation band of 600mm in 24 hours, we’ll be out of luck.
>>39 During the heavy rains in northern Kyushu in July 2017, the 1-hour rainfall near Asakura City was 169mm (actual measurement). Analyzed rainfall near Asakura City was approximately 400mm in 3 hours, 900mm in 12 hours, and 1000mm in 24 hours.
Because it was cheap, I bought a small house in a flood-prone area very close to a river, and lived in it for 18 years with no maintenance, and somehow managed to sell it and run away.
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