06 Apr 2021

06 Apr 2021

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

Increased vulnerability of European ecosystems to two compound dry and hot summers in 2018 and 2019

Ana Bastos1, René Orth1, Markus Reichstein1, Philippe Ciais2, Nicolas Viovy2, Sönke Zaehle1, Peter Anthoni3, Almut Arneth3, Pierre Gentine4,5, Emilie Joetzjer6, Sebastian Lienert7, Tammas Loughran8, Patrick C. McGuire9, Sungmin O1, Julia Pongratz7, and Stephen Sitch10 Ana Bastos et al.
  • 1Max-Planck Institute for Biogeochemistry, Hans-Knöll Str. 10, 07745, Jena, Germany
  • 2Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France
  • 3KIT, Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany
  • 4Dept. of Earth and Environmental Engineering, Columbia University, NY 10027, USA
  • 5Earth Institute and Data Science Institute, Columbia University, NY 10027, USA
  • 6CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 7Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 8Ludwig-Maximilian University, Geography Dept., Luisenstr. 37, 80333, Munich, Germany
  • 9Department of Meteorology, Department of Geography Environmental Science, and National Centre for Atmospheric Science, University of Reading, Earley Gate, RG66BB Reading, UK
  • 10College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK

Abstract. In 2018 and 2019, central Europe was stricken by two consecutive extreme dry and hot summers (DH2018 and DH2019). The DH2018 had severe impacts on ecosystems and likely affected vegetation activity in the subsequent year, for example though depletion of carbon reserves or damage from drought. Such legacies from drought and heat stress can further increase vegetation susceptibility to additional hazards. Temporally compound extremes such as DH2018 and DH2019 can, therefore, result in an amplification of impacts by preconditioning effects of past disturbance legacies.

Here, we evaluate how these two consecutive extreme summers impacted ecosystems in central Europe and how the vegetation responses to the first compound event (DH2018) modulated the impacts of the second (DH2019). To quantify the modulating role of vegetation responses to the impacts of each compound event, we first train a set of statistical models for the period 2001–2017 to predict the impacts of DH2018 and DH2019 on Enhanced Vegetation Index (EVI) anomalies from MODIS. These estimates can be seen as the expected EVI anomalies, had the impacts of DH2018 and DH2019 been consistent with past sensitivity to climate. These can then be used to identify modulating effects by vegetation activity and composition or other environmental factors such as elevated CO2 or warming trends.

We find two regions in which the impacts of the two DH events were significantly stronger than those expected based on previous climate–vegetation relationships. One region, largely dominated by grasslands and crops, showed much stronger impacts than expected in both DH events due to an amplification of their sensitivity to heat and drought, possibly linked to changing background CO2 and temperature conditions. A second region, dominated by forests, showed browning from DH2018 to DH2019, even though dry and hot conditions were partly alleviated in 2019. This browning trajectory was mainly explained by the preconditioning role of DH2018 to the observed response to DH2019 through legacy effects, and possibly by increased susceptibility to biotic disturbances, which are also promoted by warm conditions.

Dry and hot summers are expected to become more frequent in the coming decades posing a major threat to the stability of European forests. We show that state-of-the-art process based models miss these legacy effects. These gaps may result in an overestimation of the resilience and stability of temperate ecosystems in future model projections.

Ana Bastos et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2021-19', Anonymous Referee #1, 10 May 2021
  • RC2: 'Comment on esd-2021-19', Anonymous Referee #2, 11 May 2021
  • RC3: 'Comment on esd-2021-19', Anonymous Referee #3, 18 May 2021

Ana Bastos et al.

Ana Bastos et al.


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Short summary
Temperate biomes in Europe are not prone to recurrent dry and hot conditions in summer. However, these conditions may become more frequent in the coming decades. Because stress conditions can leave legacies for many years, this may result in reduced ecosystem resilience under recurrent stress. In 2018 and 2019, central Europe was stricken by two consecutive extreme dry and hot summers, which provide two case-studies to understand how such consecutive events impact European ecosystems.