in landfill zones) in 2011; the frequency of direct and large quakes is a relative rarity. The 1923 earthquake, with an estimated magnitude of 8.3, killed 142,000 people, the last time the urban area was directly hit. Volcanic eruptions Mount Fuji is about southwest of Tokyo. There is a low risk of eruption. The last recorded was the Hōei eruption which started on December 16, 1707, and ended about January 1, 1708 (16 days). During the Hōei eruption, the ash amount was 4 cm in southern Tokyo (bay area) and 2 cm to 0.5 cm in central Tokyo. Kanagawa had 16 cm to 8 cm ash and Saitama 0.5 to 0 cm. If the wind blows north-east it could send volcanic ash to Tokyo metropolis. According to the government, less than a millimeter of the volcanic ash from a Mount Fuji eruption could cause power grid problems such as blackouts and stop trains in the Tokyo metropolitan area. A mixture of ash with rain could stick to cellphone antennas, power lines and cause temporary power outages. The affected areas would need to be evacuated. Water management Tokyo is located on the Kantō Plain with five river systems and dozens of rivers that expand during each season. Important rivers are Edogawa, Nakagawa, Arakawa, Kandagawa, Megurogawa and Tamagawa. In 1947, Typhoon Kathleen struck Tokyo, destroying 31,000 homes and killing 1,100 people. In 1958, Typhoon Ida dropped of rain in a single week, causing streets to flood. In the 1950s and 1960s, the government invested 6–7% of the national budget on disaster and risk reduction. A huge system of dams, levees and tunnels was constructed. The purpose is to manage heavy rain, typhonic rain, and river floods. Tokyo has currently the world's largest underground floodwater diversion facility called the Metropolitan Area Outer Underground Discharge Channel (MAOUDC). It took 13 years to build and was completed in 2006. The MAOUDC is a long system of tunnels, underground, with tall cylindrical tanks, each tank being large enough to fit a space shuttle or the Statue of Liberty. During floods, excess water is collected from rivers and drained to the Edo River. Low-lying areas of Kōtō, Edogawa, Sumida, Katsushika, Taitō and Arakawa near the Arakawa River are most at risk of flooding. Climate The former city of Tokyo and the majority of Tokyo prefecture lie in the humid subtropical climate zone (Köppen climate classification: Cfa), with