Japan's geography and assets vulnerable to natural disasters

Due to geographic, topographic and meteorological conditions, Japan's landscape is prone to various natural events, including earthquakes, volcanic eruptions, flooding, typhoons, torrential rain and heavy snowfall. Recent impacts of climate change are further aggravating the magnitude and frequency of disasters.

Japan's share of seismic activity globally represents its vulnerability to earthquakes and associated disasters like tsunamis. Between 2000 and 2009, 1,036 seismic activities larger than MW6.0 were recorded worldwide. Of these, 212 events, or approximately 20% of the world's total, were recorded just in Japan (Cabinet Office, Government of Japan, 2012). More recently, in 2011, the Great East Japan Earthquake (GEJE) that ruptured off the Pacific coast of north-eastern Honshu recorded a magnitude of MW9.0 and was the fourth-largest earthquake recorded worldwide since 1900 (USGS, 2015). It generated recorded tsunami waves of up to 9.3 metres and run-up heights of 35 metres that inundated 560 square kilometres of the Tohoku region (Central Disaster Prevention Council, Technical Investigation Committee, 2011) (for an image of the coastal inundation, see Figure 3).

Japan's geography is also prone to water-related disasters, including floods and storm surge. For instance, rivers in Tokyo are at a higher elevation than in other urban areas, unlike some major rivers in Europe (see Figure 4). These rivers are steep and narrow, thus increasing the potential for flash floods during torrential rainfall. This is significant considering that 50% of the total population and 75% of total assets are agglomerated in these flood-prone areas: 5.4 million people live below sea level; 4 million of which are within Japan's three largest bays of Osaka, Ise and Tokyo (MLIT, 2007a). These geographic conditions, as well as exposure to hazards – that is, the agglomeration of population and assets in vulnerable areas – have made the country highly vulnerable to water-related disasters. The effects of climate change, such as sea-level rise and more frequent typhoons, also further expose people and assets to risk.

Institutional and legislative frameworks relevant to spatial risk management

Due to the recurrent nature of natural disasters in Japan, the government has developed institutional and legislative frameworks for natural disaster management.