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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/nhess-2018-55
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Mar 2018
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Natural Hazards and Earth System Sciences (NHESS).
Changing seasonality of moderate and extreme precipitation events in the Alps
Stefan Brönnimann1,2, Jan Rajczak3, Erich Fischer3, Christoph C. Raible1,4, Marco Rohrer1,2, and Christoph Schär3 1Oeschger Centre for Climate Change Research, University of Bern, Switzerland
2Institute of Geography, University of Bern, Switzerland
3Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
4Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
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 do not. 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 yrs 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 fall, 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 behavior 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 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.
Citation: Brönnimann, S., Rajczak, J., Fischer, E., Raible, C. C., Rohrer, M., and Schär, C.: Changing seasonality of moderate and extreme precipitation events in the Alps, Nat. Hazards Earth Syst. Sci. Discuss., https://doi.org/10.5194/nhess-2018-55, in review, 2018.
Stefan Brönnimann et al.
Stefan Brönnimann et al.

Data sets

Daily precipitation and temperature time series from multiple climate model simulations for the Aare river catchment (Switzerland) J. Rajczak, S. Brönnimann, E. M. Fischer, C. C. Raible, M. Rohrer, and C. Schär https://doi.pangaea.de/10.1594/PANGAEA.886881
Stefan Brönnimann et al.

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Short summary
Heavy precipitation events in Switzerland are expected to become more intense, but seasonality also changes. Analyzing a large set of model simulations, we find that annual maximum rainfall events become less frequent in late summer and more frequent in early summer and early fall. The seasonality shift is related to summer drying. Results suggest that changes in the seasonal cycle need to be accounted for when preparing for moderately extreme precipitation events.
Heavy precipitation events in Switzerland are expected to become more intense, but seasonality...
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