December 16, 2004
The Ministry of the Environment issued a report about the ground subsidence in Japan, integrating the leveling results gathered by the national and local governments in FY 2003.
The ground has subsided by 2 cm or more in six regions, and the total area of ground subsidence was 3 km2. These values for both subsidence and number of regions were all time low record since the survey started. The highest subsidence was 4.2 cm leveled in the Ishinomaki area (Ishinomaki City) of Miyagi Prefecture.
1. State of Ground Subsidence in Japan in FY 2003
In FY 2003, there is one region (none in FY 2002) which recorded annual ground subsidence over 4 cm with the subsided area totaling under one km2 (0 km2 in FY 2002). Six regions recorded annual ground subsidence of 2 cm or more (8 regions in FY 2002), with the subsided area totaling 3 km2 (461 km2 in FY 2002) (Fig.1).
The greatest level of annual ground subsidence in FY 2003 was 4.2 cm that took place in Minamihama-cho, Ishinomaki City of Miyagi Prefecture.
2. Changes in the Area of Ground Subsidence
In terms of changes in the number of regions experiencing ground subsidence and changes in the total area of ground subsidence since the Ministry of the Environment started its survey in FY 1978, the number of the region where the ground subsided by 2 cm or more in FY 2003 was the minimum, with totaling 3 km2 which was the least ever.
The ground subsidence in Japan is generally on a downward trend, however, it can hardly be said that the trend has stabilized. As shown in Fig. 2, there is the possibility of abrupt ground subsidence triggered by drought, as seen in FY 1994.
The number of regions with 2 cm or more of ground subsidence has remained unchanged from six to nine since FY 1999, though the regions surveyed are not the same in each fiscal year.
3. Measures for Ground Subsidence
The following measures have been taken to prevent ground subsidence.
| (1) | Regulation on the pumping of groundwater |
Regulation on pumping-up of groundwater for industrial use and for air-conditioning of buildings is implemented in the designated areas in ten prefectures and in four prefectures in pursuant to the Industrial Water Law (under the co-jurisdiction of the Ministry of the Environment and the Ministry of Economy, Trade and Industry) and the Law concerning the Regulation of Pumping-up of Groundwater for Use in Buildings respectively. In addition, 25 prefectures and 301 municipalities enacted ordinances to regulate the pumping-up of groundwater as of August 2004.
| (2) | Measures based on the Guideline of Measures for Preventing Ground Subsidence |
The Ministerial Council concerned with Measures for the Prevention of Ground Subsidence formulated a Guideline of Measures for Preventing Ground Subsidence for Nobi Plain, Chikugo-Saga Plain, and Northern Kanto Plain in order to implement comprehensive measures suitable to local conditions. In accordance with this guideline, the national and local governments have implemented various measures.
| (3) | Monitoring and studies |
Local governments monitor ground subsidence and measure the level of groundwater using leveling and groundwater observation wells.
| (4) | Programs concerning ground subsidence |
The national and local governments implement programs to secure and supply surface water as a substitute for groundwater, and undertake restoration programs to help areas recover from damages caused by ground subsidence, in addition to programs to prevent disasters such as flooding, high tides, and tidal waves.
| (5) | Raising awareness for the prevention of ground subsidence by providing information |
To raise awareness for the prevention of ground subsidence and to facilitate the work of national and local government officials, the Ministry of the Environment posts a "National Ground Environment Information Directory" on its website to provide information on ground subsidence, groundwater levels, regulations regarding the pumping-up of groundwater.
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| * Fig. 1 | State of Ground Subsidence in Japan in FY 2003 |
| * Fig. 2 | Changes in Total Area of Ground Subsidence in Japan |