Global warming to heighten flooding risk

Global warming will significantly increase the risk of July torrential downpours and flooding in parts of the nation by the end of the century, a research team said Wednesday.

The team, led by Akira Noda of the Meteorological Research Institute, made the projections using the Earth Simulator, an ultrahigh-speed parallel supercomputer system developed by Japan to forecast complex global weather phenomena, including climate change.

The Earth Simulator, completed in 2002, can do 36 trillion calculations per second on such things as torrential downpours.

According to the findings, the average daily rainfall in July at the end of the 21st century will have increased by several millimeters compared with before 1990, team members said. The increase will be particularly large along the Pacific coast in and to the south of the Kanto region.

Southern Kyushu will see a rise of more than 7 mm in the daily average and will face higher risks of flooding and mudslides, they said.

The calculations for southern Kyushu also suggest that the area’s monthly rainfall could increase to more than 500 mm from the current level of about 300 mm.

The team found that in other areas, including inland Honshu, the Tohoku region and Hokkaido, rainfall is projected to decrease slightly, while a 3 mm to 4 mm drop in rainfall is expected in Taiwan and the Korean Peninsula’s central region.

It also said the number of tropical depressions will drop by about 20 percent, but that probably each one will grow in intensity, meaning that Japan will be harder hit by typhoons, which develop from tropical depressions.

Noda and his team developed a computation model of the Earth’s atmosphere that was marked into 20-sq.-km grids, and another East Asia model, marked every 5 sq. km.

The resulting data were collected from the models on the premise that the average global temperature will rise more than 2 degrees by 2100.

The team will present its findings at the Earth Simulator Center Symposium next month in Tokyo.