For the first time in 12 years, the Tokyo Metropolitan Government on Wednesday attempted, on a trial basis, to artificially produce rain to cope with lower-than-average water levels in a Tama River reservoir.
Lack of rain in recent months has affected levels at dams across the Kanto region.
Ground-based generators were used at around 2 p.m. Wednesday at sites in Okutama, western Tokyo, and Koshu, Yamanashi Prefecture, to send a vapor of silver iodide mixed with acetone into the air.
When the vapor reaches an altitude of 4,000 to 5,000 meters, it freezes and condenses in the clouds, producing rain.
According to the metropolitan government, about 10 mm of rain fell upstream of the Ogouchi Dam in Okutama in an hour from around 5 p.m., while about 11 mm was registered downstream in one hour from around 2 p.m.
“It is likely the rain that fell upstream of the dam was induced by the (rain) generators,” a metropolitan government official said.
Officials said that they will decide whether to run the generators more extensively depending on the dams’ storage levels.
The dams along the Tone River were at 47 percent of capacity as of Wednesday, while dams along the Tama River were at 69 percent. Due to a water shortage, the metro government on July 24 cut by 10 percent the water taken from the dams along the Tone River.