Abstract
The annual variation of extreme precipitation in Japan was analyzed using hourly data at 981 stations for 36 years (1979-2014). Except over the Nansei Islands, the intensity of hourly extreme precipitation (Pext) defined by upper 0.1% cases is found to show a unimodal annual variation with a peak in midsummer, unlike total precipitation amount which has a bimodal annual variation with two peaks of Baiu and Shurin. The dependence of Pext on mean temperature is close to or slightly lower than the Clausius-Clapeyron (CC) rate of 6-7%/K, indicating that the annual variation of extreme precipitation is strongly linked to that of saturation vapor amount. On the other hand, Pext is different according to regions by several tens of percent for a fixed temperature. This fact suggests the influence of geographical factors on its spatial distribution. As for 24-hour precipitation, Pext shows larger deviation from the CC scaling and larger regional differences than that of hourly precipitation, implying stronger control of synoptic effects in generating long-lasting heavy rainfall.
