摘要：The intensity of precipitation events is expected toincrease in the future. The rate of increase depends on thestrength or rarity of the events; very strong and rare eventstend to follow the Clausius–Clapeyron relation, whereasweaker events or precipitation averages increase at a smallerrate than expected from the Clausius–Clapeyron relation.An often overlooked aspect is seasonal occurrence of suchevents, which might change in the future. To address theimpact of seasonality, we use a large ensemble of regionaland global climate model simulations, comprising tens ofthousands of model years of daily temperature and precipitation for the past, present, and future. In order to make thedata comparable, they are quantile mapped to observationbased time series representative of the Aare catchment inSwitzerland. Model simulations show no increase in annualmaximum 1-day precipitation events (Rx1day) over the last400 years and an increase of 10 %–20 % until the end of thecentury for a strong (RCP8.5) forcing scenario. This fits witha Clausius–Clapeyron scaling of temperature at the eventday, which increases less than annual mean temperature. Animportant reason for this is a shift in seasonality. Rx1dayevents become less frequent in late summer and more frequent in early summer and early autumn, when it is cooler.The seasonality shift is shown to be related to summer drying. Models with decreasing annual mean or summer meanprecipitation show this behaviour more strongly. The highest Rx1day per decade, in contrast, shows no change in seasonality in the future. This discrepancy implies that decadalscale extremes are thermodynamically limited; conditionsconducive to strong events still occur during the hottest timeof the year on a decadal scale. In contrast, Rx1day eventsare also limited by other factors. Conducive conditions arenot reached every summer in the present, and even less soin the future. Results suggest that changes in the seasonalcycle need to be accounted for when preparing for moderately extreme precipitation events and assessing their socioeconomic impacts.
