Climate change effects on the localized heavy rainfall event in northern Japan in 2022: Uncertainties in a pseudo-global warming approach

This study used the pseudo-global warming (PGW) method in the Weather Research and Forecasting (WRF) model to examine the effects of climate change on localized heavy rainfall events in the Tohoku and Hokuriku regions in August 2022. This heavy rainfall event is one of the representative cases of heavy rainfall in the region, in which water vapor transport from the Sea of Japan is a key factor, and its frequency and magnitude are projected to increase with climate change. Our modeling results showed that the simulated 48-h precipitation under the projected 2090s warming conditions increased by 34.6 % compared to precipitation without consideration of future warming effects. In general, the amount of water vapor in the atmosphere and convection instability over the ocean increased with future warming. While the rate of increase in water vapor is generally consistent with Clausius-Clapeyron scaling (7 %/K) based on surface temperature rise, the 48-h cumulative precipitation notably exceeds this scaling rate, even larger than triple Clausius-Clapeyron scaling. This increase in precipitation is driven by a combination of thermodynamic effects—such as enhanced water vapor content with rising temperatures—and dynamic effects, including strengthened updrafts. We showed that the model domain location can significantly affect the simulated precipitation and its changes in PGW simulations. For instance, a 29.2 % change in 48-h precipitation was observed solely due to the geospatial shift of the innermost domain. This finding indicates the importance of the model domain location as a source of uncertainty in the PGW method.