KUMAMOTO (Kyodo) Kumamoto Family Bank's unique temperature-based time deposit is proving popular with environmentally conscious clients.

The time deposit, which gives customers a higher interest rate if this summer proves cooler than last summer, starts with an interest rate of 0.25 percent. But that will nearly double to 0.4 percent if the average temperature in Kumamoto in August stays the same or drops below the average of 28.3 degrees recorded last year, the bank said.

The interest rate for the time deposit will hold for a year, the bank said. After that, it will revert to the interest rate for regular one-year time deposits, it said. The minimum deposit is 500,000 yen.

The new time deposit, launched June 15, will be available through Aug. 18 or until the product attracts total deposits worth 15 billion yen, the bank said.

The summer time deposit ended up being the bank's biggest first-day launch for a new product, it said.

"People who are conscious about the environment probably thought it was interesting," a bank official said.