24 Jun 2022
24 Jun 2022

Analysis of multi-seasonal meteorological storylines leading to reduced forest greenness in Europe in 2000–2020

Mauro Hermann1, Matthias Röthlisberger1, Arthur Gessler2,3, Andreas Rigling2,3, Cornelius Senf4, Thomas Wohlgemuth2, and Heini Wernli1 Mauro Hermann et al.
  • 1Institute for Atmospheric and Climate Science (IAC), ETH Zürich, Zurich, Switzerland
  • 2Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zurich, Switzerland
  • 3Institute of Terrestrial Ecosystems (ITES), ETH Zürich, Zurich, Switzerland
  • 4Ecosystem Dynamics and Forest Management Group, Technical University of Munich, Freising, Germany

Abstract. Recent forest decline in Europe is strongly influenced by meteorological conditions imposed by seasonal variations of temperature, T2m, and precipitation, P, and can be monitored with forest greenness. This study quantitatively investigates anomalous characteristics of the three-year meteorological storyline preceding events of reduced forest greenness in Europe's temperate and Mediterranean biome in the phase space of seasonal-mean anomalies of (T2m, P). A specific focus is on the amplitude, persistence, and co-variability of these anomalies. A pragmatic approach based on remote sensing observations of normalized difference vegetation index NDVI serves to identify low forest NDVI events at the 50 km scale in Europe in June to August 2000–2020. An independent forest disturbance data set is used to qualitatively validate the identified more than 1'500 low NDVI events. These events occur in summers with particularly dry and hot conditions but their meteorological storylines feature significant anomalies during multiple seasons preceding the events, with clear differences between the two biomes. In the Mediterranean biome, the anomalously dry conditions persist over more than 1.5 y prior to the events, whereas T2m is anomalously warm only during the last 0.4 y. In contrast, in the temperate biome, T2m is anomalously large during most of the 2.5 y prior to the events and, most interestingly, the autumn/winter preceding the events is characterized by anomalously wet and warm conditions. These anomalies potentially induce a negative legacy on the following summer drought. The seasonal-mean anomalies of P are strongly determined by synoptic-scale weather systems, such that long dry periods are characterized by a deficit of cyclones and an excess of anticyclones. A final analysis investigates the peculiarities of low NDVI events that occur in two consecutive summers and the potential role of drought legacy effects. In the temperate biome, the second event summer of an event sequence has less hot and less dry anomalies than the first one and than during a single event. In summary, detailed investigations of the multi-annual meteorological storyline of low forest NDVI events provided clear evidence that anomalies of surface weather and synoptic-scale weather systems over time periods of up to 2.5 y can negatively impact European forest activity, with important differences between the temperate and Mediterranean biomes.

Mauro Hermann 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 egusphere-2022-425', Anonymous Referee #1, 19 Jul 2022
  • RC2: 'Comment on egusphere-2022-425', Anonymous Referee #2, 14 Aug 2022

Mauro Hermann et al.

Mauro Hermann et al.


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Short summary
Recent forest decline requires understanding forest response to multi-seasonal meteorology. We investigate meteorology over 3 years preceding events of low forest greenness in Europe in 2000–2020 in a highly systematic and quantitative way. We identify time periods when meteorological variables and weather systems are significantly anomalous or persistent. Our interdisciplinary results present progress in understanding how changing meteorology will impact forest performance in this century.