Table of ContentsWhen devastating floods caused by heavy rain make headlines, the concern about the safety of our own neighborhoods becomes all consuming. For those contemplating a home purchase in Tokyo, understanding the intricacies of flood hazard maps, inundation prediction areas, and the distinctions between external and inland flooding is vital. This article aims to shed light on these essential aspects, providing valuable insights for informed decision-making.Call or email us here >>Tokyo Flood Hazard Map and Inundation Prediction Area Map: DifferencesIn Tokyo, flood hazard maps and inundation prediction area maps can be viewed on the websites of each local government and the website of the Tokyo Metropolitan Bureau of Construction. Both maps are useful for finding out the danger zone and how much flooding will occur in the event of flooding due to heavy rain. This chapter provides an overview and differences between flood hazard maps and expected inundation areas.What is the Tokyo Metropolitan Flood Hazard Map?A flood hazard map is a map designed to help with disaster prevention and evacuation in case a river overflows due to heavy rain. Hazard maps are created by each local government, and in the case of flood hazard maps in Tokyo, 23 wards, 26 cities, and 2 towns have prepared and published them. You can check the list of wards and cities published on the website of the Tokyo Metropolitan Government Bureau of Construction.The Flood Hazard Maps, compiled by individual local governments within Tokyo:delineate hazardous zonesassess danger levels designate evacuation sites and routesThese maps employ a color-coded system to convey the risk levels visually, aiding quick comprehension. Evacuation locations and evacuation routes are also useful information in case of emergency, so we recommend that you check carefully in advance when buying a house.What is the Inundation Prediction Area Map of Tokyo?Inundation Prediction Area Maps, drawn up by the Tokyo Metropolitan Government, focus on predicting inundation depths in case of flooding. Divided into 14 zones, these maps outline dangerous areas and their associated risk levels. Notably, they encompass information about both external and inland flooding, offering a comprehensive overview of flood-prone regions.Distinguishing features between Flood Hazard maps and Inundation Prediction Area MapsThere are three differences between flood hazard maps and inundation prediction area maps:Creator: Flood hazard maps are drawn up by local ward municipalities, ensuring a localized understanding of flood risks. Conversely, inundation prediction area maps are developed by the urban flood damage countermeasure liaison committee, focusing on specific river areas to provide in-depth insights.Display: Flood hazard maps are tailored to the unique needs of individual wards and municipalities, enabling precise identification of danger zones and evacuation routes at the local level. In contrast, inundation prediction area maps are river-focused, offering a broader perspective on flood-prone regions within specific river areas.Information: Flood hazard maps comprehensively outline evacuation routes and locations, providing vital information for swift emergency response. Inundation prediction area maps, while rich in data about flood depths and risk levels, do not include specifics such as evacuation locations.For individuals seeking to assess flood risks in their current or potential residence, the user-friendly "Flood Risk Search Service" offers a seamless way to access crucial information based on inundation prediction area maps. This valuable tool equips residents with the knowledge needed to make informed decisions, ensuring their safety and preparedness in the face of potential flooding events.Tokyo Flood Hazard Map and Inundation Prediction Area Map: External FloodingExternal flooding is a phenomenon in which the water level of a river rises due to heavy rain and overflows over the embankment, or the levee breaks and floods the urban area. External flooding is more likely to occur when heavy rain lasts for a long time, and once a river overflows, water flows into the urban area at once in a short time. Therefore, damage is likely to spread over a wide area, and it takes time for the water to recede.What is the expected damage caused by external flooding?External flooding can result in significant damage, including: Submerged or washed-away cars Flooded houses Delays in escape for vulnerable populations such as the elderly and childrenIf you are in a car in the danger zone and flooding occurs, get out of the car immediately and evacuate to a higher place. If you live in a house with more than two floors and flooding occurs, evacuate to the upper floors immediately. External flooding deepens in a short period of time, so there is a risk that children and the elderly will be delayed in escaping. To evacuate immediately, check the flood hazard map carefully in advance for evacuation sites and routes.Where are the places where external flooding is likely to occur?Places where external flooding is likely to occur are areas around rivers. If there is a river near the property you are about to purchase, check the flood hazard map and inundation prediction area map to see how likely the area is of flooding in the event of a flood. If you currently live in an area prone to flooding, preparedness is key. Simulating evacuations, securing belongings, and investing in tools like water stop boards or sandbags can provide essential safeguards against external flooding.Tokyo Flood Hazard Map and Inundation Prediction Area Map: Inland FloodingInland flooding, a consequence of rainwater accumulation exceeding sewer drainage capacities, presents unique challenges. This phenomenon manifests in two primary ways: inundation, where water gradually spreads due to overwhelmed drainage systems, and flooding, wherein rising river waters flow back, inundating urban areas.Anticipated Impact of Inland FloodingWhile inland flooding typically unfolds at a slower pace compared to external flooding, its subtle onset can lead to delayed evacuation if one isn't vigilant. A specific example occurred in October 2019, when Typhoon No. 19 unleashed unprecedented heavy rains, causing the Tama River to swell dramatically. This deluge resulted in the inundation of 40 homes in Setagaya and Ota wards, prompting the urgent evacuation of approximately 17,000 residents. This event illustrates the substantial human and material toll that inland flooding can exact, underscoring the need for proactive preparedness and swift response measures in vulnerable areas.Vulnerable Areas Prone to Inland FloodingIdentifying regions susceptible to inland flooding is essential for proactive disaster preparedness. Such areas include:Low Altitude Areas: These locations are predisposed to rainwater accumulation due to their geographical positioning, heightening the risk of inundation during heavy downpours.Indented Areas like Valleys: Valleys, with their natural depressions, often trap rainwater, creating a breeding ground for inland flooding. The topography slows drainage, increasing the potential for water accumulation.Urban Areas with Asphalt Pavement: Urban locales covered in impermeable asphalt face a unique threat. Rainwater struggles to seep through the solid surface, exacerbating the risk of flooding.To safeguard against these risks, it's crucial to take preventive measures. Regularly checking evacuation routes and understanding both the internal and external flood risks is paramount. Additionally, enhancing rainwater drainage by keeping house gutters clean and well-maintained can significantly reduce the likelihood of inland flooding. Proactive measures, combined with a comprehensive understanding of vulnerable areas, form the foundation for effective flood mitigation strategies.In Conclusion In conclusion, comprehending the nuances of flood hazard maps, inundation prediction areas, external flooding, and inland flooding is essential for prospective homebuyers in Tokyo. The differences between these maps lie in their display units, posted information, and creators, each offering unique perspectives on flood risks. By leveraging this knowledge, individuals can make informed decisions when selecting a residence, ensuring their safety and security in the face of potential natural disasters.Mr.LAND is a real estate agency based in Tokyo, Japan with over 30 years experience in the industry. At the Global Division, we specialize in helping international clients buy and sell real estate in Japan with full support in English. We pride ourselves in tailoring every transaction to meet the needs of each client. DM us to discuss your real estate needs anytime! We would love to hear from you!