Preprints
https://doi.org/10.5194/wcd-2022-45
https://doi.org/10.5194/wcd-2022-45
 
17 Aug 2022
17 Aug 2022
Status: this preprint is currently under review for the journal WCD.

European heatwaves in present and future climate simulations: A Lagrangian analysis

Lisa Schielicke1,2 and Stephan Pfahl1 Lisa Schielicke and Stephan Pfahl
  • 1Institut für Meteorologie, Freie Universität Berlin, Berlin, Germany
  • 2Institut für Geowissenschaften, Abteilung Meteorologie, Universität Bonn, Bonn, Germany

Abstract. Heatwaves are prolonged periods of anomalously high temperatures that can have devastating impacts on the environment, society and economy. In the recent history, heatwaves have become more intense and more numerous over most continental areas and it is expected that this trend will continue due to the ongoing global temperature rise. This general intensification may be modified by changes also in the underlying thermodynamical and dynamical processes. In order to study potential changes in heatwave characteristics and dynamics, we compare Lagrangian backward trajectories of air streams associated with historic (1991–2000) and future (2091–2100) heatwaves in six different European regions. We use a percentile-based method (Heat Wave Magnitude Index daily) to identify heatwaves in a large ensemble of climate simulations (Community Earth System Model – Large Ensemble (CESM-LE) with 35 members). In general, we find that air parcels associated with heatwaves are located to the east or inside the respective regions three days prior to the events. For future heatwaves, the model projects a north-/northeastward shift of the origin of the air masses in most study regions. Compared to climatological values, air streams associated with heatwaves show a larger temperature increase along their trajectory, which is connected to stronger descent and/or stronger diabatic heating when the air parcels enter the boundary layer. We find stronger descent associated with adiabatic warming in the northern, more continental regions and increased diabatic heating in all regions (except of the British Isles) in the simulated future climate. The enhanced diabatic heating is even more pronounced for heatwaves over continental regions. Diabatic temperature changes of near-surface air are driven by sensible heat fluxes, which are stronger over dry soils. The amplified diabatic heating associated with future heatwaves may thus be explained by an additional drying of the land surface.

Lisa Schielicke and Stephan Pfahl

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2022-45', Anonymous Referee #1, 25 Aug 2022
  • RC2: 'Comment on wcd-2022-45', Anonymous Referee #2, 08 Sep 2022
  • EC1: 'Comment on wcd-2022-45', Tim Woollings, 12 Sep 2022

Lisa Schielicke and Stephan Pfahl

Lisa Schielicke and Stephan Pfahl

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Short summary
Future European temperature extremes associated with heatwaves will be even more amplified compared to the mean increase of summer temperatures. Following the airstreams associated with heatwaves backwards in time shows, that this amplification is probably linked to a feedback between boundary-layer air and dryer soils. Moreover, in some regions stronger descent contributes to a further amplification of 2 m temperatures.