Vertical profile of the scaling of water vapor with respect to temperature

The intensities of heavy rainfall events are expected to increase as climate warms, because the atmosphere can hold more water vapor at a rate of ~7% per 1 °C rise in temperature according to the Clausius-Clapeyron (CC) equation. In this study, we explored the scaling of water vapor in terms of specific humidity and saturation vapor pressure with respect to the temperature at different atmospheric levels to understand their variation and efficacy at each atmospheric level in causing heavy rainfall. For this, we analyzed d4PDF dataset (database for Policy Decision making for Future climate change) at 20 km grid resolution in two climate periods (1951-2010 and 2051-2110 with 4K warming) over different regions of Japan. We find that the scaling patterns of the vertical profile are mostly similar in both the specific humidity and saturation vapor pressure during rainy days. At lower levels (below 850 hPa), the rate of change of specific humidity varies within the range of 6.9-7.5%/°C in present climate, while at 500 hPa the rate over southern Japan corresponds to 5.2%/°C and that over other regions shows within 6.9-8.9%/°C. These rates in future climate show slightly weaker, but the magnitude of the specific humidity with respect to temperature show increased values at all the levels and prolonged to another 4°C which may fuel the rainfall events more and ultimately would bring much intensified heavy rainfall events in future warming climate.