Only 40 percent of dams in Japan can pre-emptively release water held in the reservoirs behind them prior to heavy rains to mitigate flood risks, a Kyodo News survey showed Monday.

Following recent typhoons and other extreme weather incidents, the lack of a pre-release function forced some dam operators to carry out an emergency discharge only after water levels approached their limit. During torrential rain in western Japan in 2018, a number of people died in swollen rivers after water had been released.

The government has been calling for dam operators to prepare the function for strategic release and the active management of water levels. But improvement work will likely bring various challenges, including high costs.

The survey, conducted last month, found that 246 out of 559 dams operated by 57 organizations throughout the country are able to pre-release water prior to forecast rainfall.

Of the 45 operators who said they have difficulty doing so, they cited a number of reasons including the structures of existing dams, which can lack discharge gates or have discharge conduits with limited drainage capacity.

One of the respondents said that if they pre-release water but then no rain falls, the resulting water shortage entails risks to farmers and water utility companies, and negatively impacts society at large.