Response of Simulated Extreme Precipitation to Thermodynamic Changes in Pseudo-Global Warming

The pseudo-global warming (PGW) method has been popularly used to estimate the climate change effects on the event of interest. This study examined the uncertainties in the PGW method, including the variable selection and model domain setting, through its application to localized heavy precipitation in mesoscale convective systems in Japan. This study used the Weather Research and Forecasting (WRF) model version 4.1.2 to simulate the target heavy precipitation, which is the August 2022 heavy rainfall in the Tohoku and Hokuriku regions exceeding 600mm in 48-hr. As a result of the PGW experiment, when only the air temperature warming effect was considered, the basin-averaged 48-hour accumulated precipitation significantly increased (almost doubled). On the other hand, when air temperature and sea surface temperature warming effects were considered, the accumulated precipitation did not change significantly compared to the present climate, while the rainfall became more intense and shorter in duration. The location and duration of the convergence zone in the lower to middle atmosphere were found to be critical to the precipitation increase in the basin scale. Further, the model domain setting was found to be quite sensitive to the simulated rainfall in the PGW experiment. Our findings emphasize the importance of the variable selection and model domain setting in the PGW analysis for examining localized heavy rainfall changes under climate change.