The Tokyo Metropolitan Government has revised its flood prevention guidelines for underground spaces in the capital for the first time in 17 years amid abnormal weather conditions in recent years, with disaster plans updated to include artificial intelligence-based risk assessments.

The guidelines were revised earlier this month to implement preventive measures for underground spaces that are considered to be at the highest risk of flooding, such as shopping malls and subway stations, as well as rooms in privately owned buildings and houses that are partially or fully below ground.

The revision includes implementing AI technologies to process data on past damage and weather patterns as well as the respective area¡¯s topography data to calculate the risk of underground facilities flooding and the best route of evacuation.

The Tokyo government hopes to update flood prevention plans for underground facilities to incorporate measures such as the installation of flood guards and contingencies such as evacuation plans.

Other revisions to the guidelines include establishing a timeline of who does what at each step of the potential flooding so officials in charge know how to react in times of disaster.

In the event of a disaster, security cameras and flood sensors will be used to assess the situation.

There are currently around 72,000 underground spaces in the city, a slight increase from 2008 when the previous guidelines were made. Among them, nearly half are public facilities including shopping malls and various buildings. Eight of them are large-scale underground streets, comprising a total of 213,000 square meters.

Major underground shopping malls include the Yaechika shopping center at Tokyo Station and four large facilities at Shinjuku Station.

The guidelines are aimed at raising awareness among operators of such facilities whom the Tokyo government is looking to work with to implement the various flood-prevention measures.

The revisions follow recent years¡¯ occurrences of abnormal weather conditions across Tokyo, which now experiences more intense rainfall throughout the year than it did when the previous guidelines were issued. Severe rainfall in August 2024, for example, caused several major underground train stations, including Azabu-Juban and Ichigaya stations, to be inundated.

According to projections by the Japan Meteorological Agency, such cases of intense rainfall are forecast to increase over the next several decades. It is estimated that instances of heavy rainfall of more than 50 millimeters per hour will increase in the Kanto region and although typhoon occurrences are expected to go down, the intensity of each is projected to increase, leading to more rain.