Contrasting response of European forest and grassland energy exchange to heatwaves

Adriaan J. Teuling (1, 2) , Sonia I. Seneviratne (1) , Reto Stöckli (3) , Markus Reichstein (4) , Eddy Moors (5) , Philippe Ciais (6, 7) , Sebastiaan Luyssaert (8) , Bart van den Hurk (9) , Christof Ammann (10) , Christian Bernhofer (11) , Ebba Dellwik (12) , Damiano Gianelle (13) , Bert Gielen (14) , Thomas Grünwald (11) , Katja Klumpp (15) , Leonardo Montagnani (16, 17) , Christine Moureaux (18) , Matteo Sottocornola (13) , Georg Wohlfahrt (19)

1 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
2 Hydrology and Quantitative Water Management Group
3 Federal Office of Meteorology and Climatology
4 MPI-BGC - Max Planck Institute for Biogeochemistry
5 WUR - Wageningen University and Research Centre
6 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
7 ICOS-ATC - ICOS-ATC
8 CNRS - Centre National de la Recherche Scientifique
9 KNMI
10 Agroscope
11 Institute of Hydrology and Meteorology [Dresden]
12 Risø DTU - Risø National Laboratory for Sustainable Energy
13 IASMA - Istituto Agrario di San Michele all'Adige
14 Department of Biology
15 UREP - Unité de recherche sur l'Ecosystème Prairial
16 Forest Services
17 Free University of Bozen-Bolzano
18 Gembloux Agro-BioTech
19 Institute of Ecology

Recent European heatwaves have raised interest in the impact of land cover conditions on temperature extremes. At present, it is believed that such extremes are enhanced by stronger surface heating of the atmosphere, when soil moisture content is below average. However, the impact of land cover on the exchange of water and energy and the interaction of this exchange with the soil water balance during heatwaves is largely unknown. Here we analyse observations from an extensive network of flux towers in Europe that reveal a difference between the temporal responses of forest and grassland ecosystems during heatwaves. We find that initially, surface heating is twice as high over forest than over grassland. Over grass, heating is suppressed by increased evaporation in response to increased solar radiation and temperature. Ultimately, however, this process accelerates soil moisture depletion and induces a critical shift in the regional climate system that leads to increased heating. We propose that this mechanism may explain the extreme temperatures in August 2003. We conclude that the conservative water use of forest contributes to increased temperatures in the short term, but mitigates the impact of the most extreme heat and/or long-lasting events.

Domaines: Sciences du Vivant [q-bio]

Adriaan J. Teuling, Sonia I. Seneviratne, Reto Stöckli, Markus Reichstein, Eddy Moors, et al.. Contrasting response of European forest and grassland energy exchange to heatwaves. Nature Geoscience, 2010, 3 (10), pp.722-727. ⟨10.1038/ngeo950⟩. ⟨hal-02663686⟩