EGU21-2754
https://doi.org/10.5194/egusphere-egu21-2754
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nonlocal soil moisture effects during European heatwaves

Ronja Bohnenblust1, Anna L. Merrifield1, Sebastian Sippel1, Isla R. Simpson2, Karen A. McKinnon3, Erich M. Fischer1, Clara Deser2, and Reto Knutti1
Ronja Bohnenblust et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 2Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 3Institute of the Environment and Sustainability, Department of Statistics, University of California, Los Angeles, CA, USA

It has been shown that European heatwaves can be significantly intensified by dry land surface conditions. While local temperature intensification through soil moisture feedbacks are well understood, the role of nonlocal soil moisture conditions has yet to be studied in more detail. Studies suggest that through modification of the atmospheric circulation, soil moisture conditions can enhance local temperatures and even evoke a remote temperature response. 

In this study, we analyze how nonlocal soil moisture – atmosphere feedbacks contribute to the development of high temperature extremes during a seasonally persistent European heatwave. We use a CESM-based global circulation model framework described in Merrifield et al. (2019), in which near-identical heatwave-inducing atmospheric circulation patterns encounter different land surface conditions. In one ensemble the whole atmosphere is constrained, allowing only local temperature intensification by the land surface. In the other ensemble only the upper atmosphere is constrained, enabling the land surface to modify the atmospheric circulation below 300hPa.

To understand what variables and processes contribute to regional heatwave intensification in some members and damping in others on a daily timescale, a refined spatio-temporal analysis of the data set was performed. We find that local daily temperature spread across ensemble members amounts to 5°C in the ensemble with unconstrained lower atmosphere, which is 4°C more than in the ensemble where the whole atmosphere is constrained, highlighting the importance of nonlocal land – atmosphere interactions. We identify atmospheric pathways through which the land surface state in one region affected the intensity of the heatwave in another region during the initiation, peak, and decay phases of the event. These heatwave intensification storylines may help to inform seasonal prediction and improve preparedness for future European heat events.

 

How to cite: Bohnenblust, R., Merrifield, A. L., Sippel, S., Simpson, I. R., McKinnon, K. A., Fischer, E. M., Deser, C., and Knutti, R.: Nonlocal soil moisture effects during European heatwaves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2754, https://doi.org/10.5194/egusphere-egu21-2754, 2021.

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