TOKYO — The Japanese capital has seen a string of “guerilla” torrential downpours this summer, including one that even flooded a metro station. As the season of sudden rainfalls continues, social media users are sharing a bit of dubious wisdom: “Places with ‘valley’ in the name are low-lying and prone to flooding.'”
They are referring to Tokyo districts with the Chinese character read as “ya” — meaning valley — in their name, such as Ichigaya and Shibuya. And indeed, torrential rains that hit the city in August did cause flooding in those areas. But, while places are often said to get their titles from real geographical features, one expert warned, “It’s dangerous to make judgments based solely on place names.”
The social media downpour
On the night of Aug. 21, about 100 millimeters of rain fell in an area around Tokyo’s Minato Ward in just an hour, prompting the Japan Meteorological Agency (JMA) to issue a “record short-term heavy rainfall” warning.
In Shibuya Ward, roads under elevated tracks were flooded, leaving vehicles stranded and stores inundated. At Tokyo Metro’s Ichigaya Station, straddling Chiyoda and Shinjuku wards, rainwater poured down the stairs at one of the entrances, flooding the interior.
Did these places flood because they were valleys, as suggested by their names? Many on social media seemed to think so, labelling any with the character for valley as dangerous. But is there really any connection between place names and geography?
According to the “Dictionary of municipal name origins” published by Tokyodo Shuppan Co., the origin of the name Shibuya is said to be “a wetland gradually narrowing between plateaus.” The Shibuya Ward website states that while there is no definitive theory behind its name, it introduces four theories, including one that the lowlands along the Shibuya River were once a narrow valley, and another that it derives from a person’s name.
Meanwhile, the name Ichigaya could refer to “the first valley” of the Yamanote Plateau, according to the Tokyo Chamber of Commerce and Industry’s website. It seems likely that the origins of both place names are connected to actual valleys.
Geography and reality
Topographic maps from the Geospatial Information Authority of Japan, show that the area around Ichigaya Station lies at the bottom of a valley with gently sloping sides.
However, even within Ichigaya, areas like the Ministry of Defense in the Ichigaya Honmura-cho neighborhood of Shinjuku Ward are on higher ground. Similarly, although Shibuya Station and its surrounding areas are situated in valley-like lowlands, other parts of Shibuya Ward are on higher elevations. The presence of “valley” in a place name does not always fully describe the local geographic features.
Place names only a reference
“Every time a disaster like an earthquake or flood occurs, discussions about ‘dangerous place names’ and ‘safe place names’ resurface, but these don’t necessarily correlate with disaster risks,” said Yoshiharu Yokoyama, the 46-year-old head of the Daichi disaster risk research institute.
While place names featuring characters like “valley,” “pond,” “swamp” and “deep” are often labeled as dangerous online, Yokoyama points out that the names often encompass various terrains. Moreover, these frequently change due to municipal mergers or urban development.
As an example, Yokoyama cited the area name “Tsudanuma” in Narashino, Chiba Prefecture, which might appear to pose a flood risk as “numa” means “swamp.” However, upon examining the geography, the area includes plateaus and elevated regions. According to the Narashino Municipal Government, the name combines the former village names of “Yatsu,” “Kuguta” and “Saginuma.”
Names including characters like “hill” or “plateau” might suggest high ground, but caution is needed, as they could refer to places created through landfills or new residential areas in lowlands.
Yokoyama emphasized, “Place names should only serve as a reference. Always check the terrain and hazard maps to assess safety.”
Hazard maps are not perfect
At the same time, Yokoyama warned, “Hazard maps are not perfect predictions, and just because an area isn’t highlighted doesn’t mean it’s safe.”
The area around Ichigaya Station’s Exit 6, which let in all that water, wasn’t marked as dangerous on the flood hazard map released by the government of Shinjuku Ward. Hazard maps are based on simulations of maximum potential rainfall, considering the terrain and rivers, to estimate flood-prone areas. However, localized heavy rains can still cause damage in unexpected places.
The Tokyo Metropolitan Government’s Q and A page for flood projections states that “flooding not fully accounted for in simulations can occur,” and advises caution in lowlands or areas with previous flooding, even if they aren’t marked on the hazard map.
Yokoyama stressed the importance of personally checking the areas where you spend your everyday life: “It’s crucial to observe for yourself whether rainwater tends to flow toward or away from your location.”
(Japanese original by Maki Kihara, Tokyo City News Department)
Flood fears: Does ‘valley’ in a Japanese place name spell disaster?
