Extreme precipitation linked to temperature over Japan: current evaluation and projected changes with multi-model ensemble downscaling

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Recent studies have revealed that an increase in surface air temperature elevates the intensity of extreme precipitation associated with the increase of water vapor in the atmosphere, according to the principle of the Clausius–Clapeyron (CC) relationship. In this study, (1) we have verified the dependence of extreme precipitation intensity on temperature (CC relationship) under current climate and (2) investigated the projected changes of the CC relationship over Japan by using multi-model ensemble downscaling experiments of three Regional Climate Models (RCMs) (NHRCM, NRAMS, WRF) forced by JRA25, as well as three General Circulation Models (GCMs) (CCSM4, MIROC5, MRI-CGCM3). Simulated extreme precipitation linked to temperatures from ensemble experiments coincides with observations that place peak temperatures around 19–22 °C. Climate scenarios (RCP4.5) of the late twenty-first century suggest a 2 °C increase of 2 m air temperature, an increase in precipitation intensities above 15 mm/day, and a decrease in weaker precipitation intensities of 10–15 mm/day. The projected change rate of the mean precipitation intensities per mean change in air temperature over Japan is found to be 2.4%/°C. Extreme precipitation intensity increases with temperatures up to 22 °C in future climate scenarios, while the peak is 20 °C for the current climate. Extreme precipitation intensities at higher percentiles are projected to have larger rates of increase (3–5%/°C in the current climate and 4–6%/°C in the future climate scenarios). A decrease of precipitation intensity at higher temperatures relates to water vapor availability. An insufficient water vapor supply for saturation at higher temperatures can lead to a decrease in cloud formation and extreme precipitation.