TOKYO - Tokyo’s Ogouchi Dam, a key water source for the capital, has fallen to its lowest level since the Heisei era, raising concerns over potential water shortages as rising temperatures intensify pressure on supply.
Temperatures climbed across Japan on April 6th, with some areas recording summer-like conditions, while one of Tokyo’s main water reservoirs edged closer to a drought crisis.
Ogouchi Dam in Okutama, which can supply up to 40 days of drinking water for Tokyo residents when full, has dropped to less than half its capacity, equivalent to just 13.5 days of supply.
Nakamura Koichi, head of the Ogouchi Reservoir Management Office at the Tokyo Metropolitan Government’s Bureau of Waterworks, said the level is the lowest recorded since the Heisei era, warning that calls for water conservation could be issued if levels continue to fall.
A visible white line along the dam wall marks where water levels once stood, with the current level measured at 62.7 meters—nearly 25 meters below normal. Land that is usually submerged has now emerged, and a bridge that once floated on the reservoir is now accessible on foot.
The reservoir’s storage rate has fallen to 33.9 percent, far below the level needed to sustain normal supply.
Visitors expressed concern, with one saying the situation appeared serious and that stronger water-saving efforts would be necessary.
Even after moderate rainfall over the weekend, the water level rose by only about 60 centimeters, equivalent to roughly 0.28 days of supply—just seven hours of drinking water for Tokyo’s population.
The Tama River system, which includes Ogouchi Dam, accounts for about 20 percent of Tokyo’s water supply, while the Tone River system provides the remaining 80 percent and is currently recovering due to snowmelt inflows.
Nakamura noted that an immediate water shortage is unlikely, adding that prolonged dry conditions are also unlikely, and the city aims to maintain stable water supply.
However, other regions are already facing direct impacts from water shortages.
In Nara Prefecture, declining levels at Ohtaki Dam have led to water restrictions for the first time in 21 years, affecting approximately 880,000 people across 24 municipalities.
In Aichi Prefecture, Ure Dam reached a storage rate of zero percent in March, prompting Toyohashi and Toyokawa cities to switch to pre-washed rice for school lunches at 112 elementary and junior high schools starting April 27th.
As water shortages spread, temperatures rose nationwide on April 6th.
Nagano City recorded 25 degrees Celsius, marking its first summer day of 2026, while central Tokyo experienced early summer conditions with a high of 23.7 degrees at 11 a.m., comparable to mid-May.
People walking in the city were seen carrying parasols and wearing short sleeves, with some waiting for traffic lights in shaded areas, creating scenes reminiscent of midsummer.
At a park in Tokyo’s Sumida Ward crowded with cherry blossom viewers, some sought relief near fountains, with one visitor saying they had switched to short sleeves and were staying hydrated and resting in the shade.
Japan is expected to see an early start to summer in 2026, with temperatures projected to rise above average during peak season and an increase in extremely hot days anticipated.
Source: FNN
