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13 Jul 2021
13 Jul 2021

The ExtremeX global climate model experiment: Investigating thermodynamic and dynamic processes contributing to weather and climate extremes

Kathrin Wehrli1, Fei Luo2,3, Mathias Hauser1, Hideo Shiogama4, Daisuke Tokuda5, Hyungjun Kim5, Dim Coumou2,3, Wilhelm May6, Philippe Le Sager3, Frank Selten3, Olivia Martius7,8,9, Robert Vautard10, and Sonia I. Seneviratne1 Kathrin Wehrli et al.
  • 1Institute for Atmospheric and Climate Science, Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
  • 2Institute for Environmental Studies, VU University Amsterdam, Amsterdam, Netherlands
  • 3Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands
  • 4Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan
  • 5Institute of Industrial Science, University of Tokyo, Tokyo, Japan
  • 6Centre for Environmental and Climate Science (CEC), Lund University, Lund, Sweden
  • 7Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 8Institute of Geography, University of Bern, Bern, Switzerland
  • 9Mobiliar Lab for Natural Risks, University of Bern, Bern, Switzerland
  • 10Institut Pierre Simon Laplace, Laboratoire des Sciences du Climat et de l’Environnement (LSCE), Gif sur Yvette, France

Abstract. The mechanisms leading to the occurrence of extreme weather and climate events are varied and complex. They generally encompass a combination of dynamical and thermodynamical processes, as well as drivers external to the climate system, such as anthropogenic greenhouse gas emissions and land-use change. Here we present the ExtremeX multi-model intercomparison experiment, which was designed to investigate the contribution of dynamic and thermodynamic processes to recent weather and climate extremes. The numerical experiments are performed with three Earth System Models: CESM, MIROC, and EC-Earth. They include control experiments with interactive atmosphere and land surface conditions, and experiments where either the atmospheric circulation, soil moisture or both are constrained using observation-based values. The temporal evolution and magnitude of temperature anomalies during heatwaves is well represented in the experiments with constrained atmosphere. However, mean climatological biases in temperature and precipitation are not substantially reduced in any of the constrained experiments, highlighting the importance of error compensations and tuning in the standard model versions. The results further reveal that both atmospheric circulation patterns and soil moisture conditions substantially contribute to the occurrence of heat extremes. Soil moisture effects are particularly important in the tropics, the monsoon areas and the Great Plains of the United States.

Kathrin Wehrli et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Reviewer comment on esd-2021-58', Paul Dirmeyer, 10 Sep 2021
  • RC2: 'Comment on esd-2021-58', Anonymous Referee #2, 17 Oct 2021

Kathrin Wehrli et al.

Kathrin Wehrli et al.


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Short summary
The ExtremeX experiment was designed to disentangle the contribution of processes leading to the occurrence recent weather and climate extremes. Global climate simulations are carried out with three climate models. The results show that temperature anomalies during heatwaves are well represented although climatological model biases remain. Further, a substantial contribution of both atmospheric circulation patterns and soil moisture conditions to heat extremes is identified.