The Meteorological Research Institute analyzed the heaviest hourly rainfall recorded in more than 980 locations across Japan between 1978 and 2013. Researchers learned that the maximum hourly rainfall intensified by about 13 percent in the past 35 years. Annual rain tends to intensify when temperatures, including water temperatures, are high.

In 2013, when Japan's average temperature was 0.3 degrees Celsius above the norm, maximum hourly rainfall was 16 percent higher than the 1978-2013 average, 19 downpours had more than 80 millimeters of rain per hour in each of the past 5 years.   That's 50 percent higher than the average figure for the same period of time three decades ago.(KH)