The Diet on Wednesday enacted a special law to promote the use of unclaimed land in the public interest, as more and more properties are expected to become available amid a decreasing population.

The act, to be fully put into effect by June next year, will enable the heads of local governments to give permission to applicants to use unattended land for up to 10 years for public purposes such as community halls, parks and health clinics. If the landowner shows up and reclaims the land, the property will be returned after the term of the land-use contract ends. If no one reclaims the land, the land-use period can be extended.

Given the rapidly aging population, unclaimed land lots are projected to increase, raising concerns that leaving them in their current state could hamper redevelopment plans and public works projects, as well as hinder efforts to rebuild disaster-hit areas.

In 2016, the total area of unclaimed land — residential, agricultural and forested properties — was estimated at about 4.1 million hectares, slightly bigger in size than the island of Kyushu, according to a private-sector study group.

The research group, which includes former internal affairs minister Hiroya Masuda, estimated that accumulated economic losses due to the neglect of such land, including damage from flooding and mudslides, could reach ¥6 trillion by 2040.

In many cases, the ownership of estates remain unknown due to the failure of owners to complete the land registration process, which costs money and is viewed as burdensome.

For local governments planning public works projects, it can also cost time and money to track down such landowners.

The law enacted Wednesday is a provisional measure and the government plans to revise related legislation by 2020 to tackle the issue.

Under the special law, simplified procedures mean the central government and local municipalities will also be able to more easily acquire the unclaimed land.

If the property is not used for the stated purpose, the governor will order the applicant to restore the land to its original state. An applicant who refuses to follow the order can be sentenced to up to one year in prison or face a fine of up to ¥300,000 ($2,700).