Abstract. The intensity of precipitation events is expected to increase in the future.
The rate of increase depends on the strength or rarity of the events; very
strong and rare events tend to follow the Clausius–Clapeyron relation,
whereas weaker events or precipitation averages increase at a smaller rate
than expected from the Clausius–Clapeyron relation. An often overlooked
aspect is seasonal occurrence of such events, which might change in the
future. To address the impact of seasonality, we use a large ensemble of
regional and global climate model simulations, comprising tens of thousands
of model years of daily temperature and precipitation for the past, present,
and future. In order to make the data comparable, they are quantile mapped to
observation-based time series representative of the Aare catchment in
Switzerland. Model simulations show no increase in annual maximum 1-day
precipitation events (Rx1day) over the last 400 years and an increase of
10 %–20 % until the end of the century for a strong (RCP8.5) forcing
scenario. This fits with a Clausius–Clapeyron scaling of temperature at the
event day, which increases less than annual mean temperature. An important
reason for this is a shift in seasonality. Rx1day events 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 mean precipitation show this behaviour
more strongly. The highest Rx1day per decade, in contrast, shows no change in
seasonality in the future. This discrepancy implies that decadal-scale
extremes are thermodynamically limited; conditions conducive to strong events
still occur during the hottest time of the year on a decadal scale. In
contrast, Rx1day events are also limited by other factors. Conducive
conditions are not reached every summer in the present, and even less so in
the future. Results suggest that changes in the seasonal cycle need to be
accounted for when preparing for moderately extreme precipitation events and
assessing their socio-economic impacts.
Changing seasonality of moderate and extreme precipitation events in the Alps
