Numerical Simulation of Heavy Rainfall in August 2014 over Japan and Analysis of Its Sensitivity to Sea Surface Temperature

Abstract

This study evaluated the performance of the Weather Research and Forecasting (WRF) model version 3.7 for simulating a series of rainfall events in August 2014 over Japan and investigated the impact of uncertainty in sea surface temperature (SST) on simulated rainfall in the record-high precipitation period. WRF simulations for the heavy rainfall were conducted for six different cases. The heavy rainfall events caused by typhoons and rain fronts were similarly accurately reproduced by three cases: the TQW_5km case with grid nudging for air temperature, humidity, and wind and with a horizontal resolution of 5 km; W_5km with wind nudging and 5-km resolution; and W_2.5km with wind nudging and 2.5-km resolution. Because the nudging for air temperature and humidity in TQW_5km suppresses the influence of SST change, and because W_2.5km requires larger computational load, W_5km was selected as the baseline case for a sensitivity analysis of SST. In the sensitivity analysis, SST around Japan was homogeneously changed by 1 K from the original SST data. The analysis showed that the SST increase led to a larger amount of precipitation in the study period in Japan, with the mean increase rate of precipitation being 13 ± 8% K −1 . In addition, 99 percentile precipitation (100 mm d −1 in the baseline case) increased by 13% K −1 of SST warming. These results also indicate that an uncertainty of approximately 13% in the simulated heavy rainfall corresponds to an uncertainty of 1 K in SST data around Japan in the study period.

Impact of SST on Present and Future Extreme Precipitation in Hokkaido Investigated Considering Weather Patterns

“…On the basis of sensitivity experiments on precipitation during August 2014, Minamiguchi et al. (2018) also revealed that warmer SST around Japan could amplify heavy rainfall events associated with typhoons and fronts. In contrast, Iizuka and Nakamura (2019) found no significant relationship between local maximum precipitation and Sea of Japan SST during a heavy rainfall event that occurred over northern Japan in August 2013.…”

“…Manda et al (2014) performed a sensitivity experiment on a torrential rainfall event that occurred in Japan in mid-July 2012, and they demonstrated that future SST warming in the East China Sea could increase the frequency of extreme precipitation events over western Japan. On the basis of sensitivity experiments on precipitation during August 2014, Minamiguchi et al (2018) also revealed that warmer SST around Japan could amplify heavy rainfall events associated with typhoons and fronts. In contrast, Iizuka and Nakamura (2019) found no significant relationship between local maximum precipitation and Sea of Japan SST during a heavy rainfall event that occurred over northern Japan in August 2013.…”