Land subsidence due to groundwater exploitation in Japan

Problems

• Land Subsidence in Japan

  Land subsidence is mainly caused by overexploitation of groundwater, and it has resulted in several problems along Japan's coastal areas, such as damage to buildings and facilities, changes in stream slopes, and increased risks of river flooding during high tides or storm surges. 
  
  In Japan, groundwater has been extensively exploited for various purposes, including industrial use, public water supply, and agriculture. This overexploitation has decreased underground water levels, causing the land to sink. The problem is particularly severe in urban areas with high water demand.
  
  Land subsidence can lead to numerous problems. It can damage buildings and infrastructure, disrupt transportation, and increase flood risks, especially in low-lying coastal areas. In Japan, where many cities are located near the coast and are already vulnerable to sea-level rise due to climate change, land subsidence further exacerbates these risks.
  
  Tokyo is one of the cities that has experienced significant land subsidence due to groundwater extraction. In the 1960s, parts of Tokyo sank at 240 mm per year. This rapid subsidence led to frequent flooding and damage to infrastructure. In response, the Tokyo Metropolitan Government implemented strict groundwater use regulations, successfully reducing the subsidence rate.
  
  However, other areas of Japan continue to face this issue. In Osaka, another major city, land subsidence due to groundwater extraction remains a significant problem. The city is located in a low-lying area near the coast, making it particularly vulnerable to flooding. 
  
  According to the flood hazard map of the Ministry of Land, Infrastructure, Transport and Tourism, most of the city of Osaka is in an area expected to be flooded. This is partly because the Yodo and Yamato Rivers, which are first-class rivers, cross from east to west, but the main reason is that Osaka is low-lying. It wasn't always like this.
  
  Osaka is Japan's largest city and has a thriving industry. There are many factories in the area and there is a high demand for groundwater, and large amounts of groundwater were pumped out during the early Showa era (December 25, 1926 to January 7, 1989). As a result, the ground subsided.
  
  In addition to these preventive works, the use of groundwater was gradually regulated as industrial water supply works planned to replace groundwater were completed.
  
  Thanks to a regulation prohibiting the use of groundwater in the city of Osaka, land subsidence in the city has gradually decreased and is now almost stopped.

• Conclusion

  Land subsidence due to groundwater exploitation is a pressing issue in Japan. While steps have been taken to address this problem, more must be done. As the water demand continues to grow, it is crucial to manage groundwater resources sustainably. At the same time, Japan's experience offers valuable lessons for other countries facing similar challenges. Through a combination of policy, technology, and planning, it is possible to mitigate the impacts of land subsidence and ensure the resilience of our cities.