Regional and vertical scaling of water vapor with temperature over Japan during extreme precipitation in a changing climate

Water vapor in the atmosphere plays a critical role in the occurrence of extreme precipitation events. As temperatures increase, the atmosphere can hold more water vapor, which leads to an increase in the intensity of extreme precipitation events. The Clausius-Clapeyron (CC) equation predicts that the intensity of extreme precipitation events will scale with temperature at a rate of approximately 7% per degree Celsius. However, previous studies have been limited to explore how the availability of water vapor varies at different pressure levels in the atmosphere on wet days. In our study, we found a strong positive relationship between specific humidity and temperature on wet days in the lower atmospheric levels over Japanese regions, while no significant relationship was found at higher levels. The rate of change of specific humidity with temperature on wet days varied by region, but was within the range of 8.3 ± 2.4% per degree Celsius. Our findings suggest that extreme precipitation events will become more intense in the future warming climate across all regions of Japan. This intensification is mainly driven by increased moisture availability on wet days, as well as changes in temperature and atmospheric dynamics, which are expected to influence extreme precipitation events.