Today's supercomputer-based weather predictions cannot accurately predict the threat of torrential rains, which can develop within minutes.

Now, an international team led by Takemasa Miyoshi, of the Riken Advanced Center for Computational Science, has used supercomputing and advanced radar observational data to accurately predict the occurrence of torrential rains in localized areas.

Fast-developing rainstorms are notoriously difficult to predict. Image credit: Pixabay. Using Riken's K computer, the researchers carried out 100 parallel simulations of a convective weather system using the nonhydrostatic mesoscale model employed by the Japan Meteorological Agency—but with 100-meter grid spacing rather than the typical 2-kilometer or 5-kilometer spacing—and assimilated data from a next-generation phased-array weather radar. With this, they produced a high-resolution, three-dimensional distribution map of rain every 30 seconds, 120 times more rapidly than the typical hourly updated systems operated at the world’s weather prediction centers today.

To test the accuracy of the system, the researchers attempted to model a real case—a sudden storm that took place on July 13, 2013 in Kyoto close enough to Osaka that it was caught by the radars at Osaka University. The simulations were run starting at 15:00 Japanese time and tested as pure simulations without observational data input, as well as with the incorporation of data every 30 seconds on 100-meter and 1-kilometer grid scales.

The simulation alone was unable to replicate the rain, while the incorporation of observational data allowed the computer to represent the actual storm. In particular, the simulation performed with 100-meter grids led to a very accurate replication of the storm compared to actual observations.

“Supercomputers are becoming more and more powerful and are allowing us to incorporate ever more advanced data into simulations," says Miyoshi. "Our study shows that in the future, it will be possible to use weather forecasting to predict severe local weather phenomena such as torrential rains, a growing problem [that] can cause enormous damage and cost lives.”