The fingerprint of the summer 2018 drought in Europe on ground-based atmospheric CO <sub>2</sub> measurements
Michel Ramonet, P. Ciais, Francesco Apadula, Jakub Bartyzel, Ana Bastos, P. Bergamaschi, Pierre-Éric Blanc, Dominik Brunner, L. Caracciolo di Torchiarolo, F. Calzolari, Huilin Chen, Łukasz Chmura, A. Colomb, Sébastien Conil, Paolo Cristofanelli, Emilio Cuevas, Roger Curcoll, Marc Delmotte, Alcide di Sarra, Lukas Emmenegger, Grant L. Forster, Arnoud Frumau, Christoph Gerbig, François Gheusi, Samuel Hammer, László Haszpra, Juha Hatakka, Lynn Hazan, Michal Heliasz, Stephan Henne, A. Hensen, Ove Hermansen, P. Keronen, Rigel Kivi, Kateřina Komínková, Dagmar Kubistin, Olivier Laurent, Tuomas Laurila, Jošt V. Lavrič, Irene Lehner, K. E. J. Lehtinen, Ari Leskinen, Markus Leuenberger, Ingeborg Levin, Matthias Lindauer, Morgan Lopez, Cathrine Lund Myhre, Ivan Mammarella, Giovanni Manca, Andrew C. Manning, Michal V. Marek, Per Marklund, Damien Martin, Frank Meinhardt, N. Mihalopoulos, Meelis Mölder, Josep-Antón Morguí, Jarosław Nęcki, Simon O’Doherty, Colin O’Dowd, Mee Ottosson, Carole Philippon, Salvatore Piacentino, Jean Marc Pichon, C. Plaß-Duelmer, Alex Resovsky, Léonard Rivier, Xavier Rodó, Mahesh Kumar Sha, Bert Scheeren, Damiano Sferlazzo, T. Gerard Spain, Kieran Stanley, Martin Steinbacher, Pamela Trisolino, Alex Vermeulen, Gabriela Vítková, Dietmar Weyrauch, Irène Xueref-Rémy, K. Yala, Camille Yver Kwok
Abstract
During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO 2 ) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO 2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO 2 gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO 2 cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO 2 due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO 2 transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO 2 uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO 2 anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO 2 anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.