Preprints
https://doi.org/10.5194/esd-2020-61
https://doi.org/10.5194/esd-2020-61

  17 Sep 2020

17 Sep 2020

Review status: this preprint is currently under review for the journal ESD.

A dynamical and thermodynamic mechanism to explain heavy snowfalls in current and future climate over Italy during cold spells

Miriam D'Errico1, Pascal Yiou1, Cesare Nardini2, Frank Lunkeit3, and Davide Faranda1,4 Miriam D'Errico et al.
  • 1Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CEA-CNRS-UVSQ, Université Paris-Saclay, IPSL, 91191 Gif-sur-Yvette cedex, France
  • 2Service de Physique de l'État Condensé, CNRS UMR 3680, CEA-Saclay, 91191 Gif-sur-Yvette, France
  • 3Meteorological Institute, CEN, University of Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany
  • 4London Mathematical Laboratory, 8 Margravine Gardens, London, W6 8RH, UK

Abstract. Cold and snowy spells are compound extreme events that have many societal impacts. Insight on their dynamics in climate change scenarios could help adaptation. We focus on winter cold and snowy spells over Italy, reconstructing 32 major events in the past 60 years from documentary sources. We show that despite warmer winter temperatures, some recent cold spells show abundant, sometimes exceptional snowfall amounts. In order to explain these compound phenomena, we perform ensembles of climate simulations in fixed emission scenarios changing boundary conditions (such sea–surface temperature, SST) and detect analogs of observed events. Our results show that the response of extreme cold weather events to climate change is not purely thermodynamic nor linked to the global average temperature increase, but crucially depends on the interactions of the atmospheric circulation at mid-latitudes with the thermodynamic feedback from warmer Mediterranean temperatures. This suggests how Mediterranean countries like Italy could observe large snowfall amounts even in warmer climates.

Miriam D'Errico et al.

 
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Miriam D'Errico et al.

Miriam D'Errico et al.

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Short summary
Climate change is already affecting weather extreme. In a warming climate, we will expect the intensity of cold spells to decrease in frequency and intensity. However, our analysis shows that the intensity of snowy cold spells events over Italy is not decreasing and that most of the extreme snowfalls occur in the very recent past. Using climate simulations, we show a key mechanism in modulating snowfall in a warming climate: the convective feedback of the Mediterranean Sea.
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