Tokyo
Tokyo Geography & Climate
Geography
Tokyo sits at the head of a bay on the Kanto plain, the largest area of flat land in Japan, and its site is both the reason for its size and its central risk.
The plain and the bay
The Kanto plain gave the city room to spread in a country that is three-quarters mountain, and Tokyo Bay gave it a port. The western wards rise onto the Yamanote uplands, a plateau of firm ground where the samurai districts and now the affluent neighbourhoods are; the eastern wards are the Shitamachi low city, built on soft alluvium and reclaimed land at or below sea level, historically the merchant and artisan quarter and still the more working-class half.
Reclaimed land
Large parts of the waterfront — Odaiba, the container terminals, much of the eastern shore — are made ground, some of it built on refuse. It is the least stable ground in the city.
Three plates
Tokyo sits above the junction of the Pacific, Philippine Sea and North American plates, which is as seismically complicated as anywhere inhabited. Small tremors are routine and a major earthquake is expected.
Rivers and floods
The Sumida, Arakawa and Tama drain the plain, and the city sits behind an enormous system of levees and an underground flood-diversion cavern north of the city that is among the largest structures of its kind.
Sinking and pumping
Groundwater extraction through the twentieth century caused parts of the eastern wards to subside by more than four metres, leaving a zone of several hundred thousand people living below high-tide level behind embankments. Pumping was curtailed from the 1960s and the subsidence largely stopped, but the low ground remains, which is why the flood defences are as elaborate as they are.
Mount Fuji
About 100 kilometres west, visible from tall buildings on clear winter days.
Climate Patterns
Tokyo has a humid subtropical climate with four distinct seasons and two of them difficult.
Summer
Late July to early September is hot and extremely humid: highs of 31 to 35°C with humidity that keeps nights above 25°C, and the urban heat island adds several degrees. It is genuinely draining, and Japan issues heatstroke alerts. Air-conditioned shops, underground passages and department stores are the standard survival strategy.
The rainy season
Tsuyu runs from early June to mid-July, when a stationary front sits over the country delivering weeks of grey, humid, drizzly weather. It is not the worst time to visit — hydrangeas are out and sites are quiet — but it is not pleasant.
Typhoons
August to October, with a few each year passing close enough to shut the trains and flights for a day. Warnings are accurate and well publicised.
Winter
December to February is cold but dry and strikingly sunny: 5 to 12°C by day, close to freezing at night, with very little rain and the clearest air of the year. Snow falls once or twice and paralyses the city.
The heat island
Tokyo has warmed by roughly three degrees over the past century, about three times the global average, because of the sheer density of concrete, asphalt and air-conditioning exhaust. Nights no longer cool down in summer the way they did, which is the part residents notice, and it is why the city now plants rooftop gardens and paves some roads with water-retaining surfaces.
Spring and autumn
Short and excellent. Cherry blossom in late March and early April; autumn colour in late November.