Supplementary figures S1-S6 from The fingerprint of the summer 2018 drought in Europe on ground-based atmospheric CO<sub>2</sub> measurements
Creators: name: M. Ramonet
name: P. Ciais
name: F. Apadula
name: J. Bartyzel
name: A. Bastos
name: P. Bergamaschi
name: P. E. Blanc
name: D. Brunner
name: L. Caracciolo Di Torchiarolo
name: F. Calzolari
name: H. Chen
name: L. Chmura
name: A. Colomb
name: S. Conil
name: P. Cristofanelli
name: E. Cuevas
name: R. Curcoll
name: M. Delmotte
name: A. Di Sarra
name: L. Emmenegger
name: G. Forster
name: A. Frumau
name: C. Gerbig
name: F. Gheusi
name: S. Hammer
name: L. Haszpra
name: J. Hatakka
name: L. Hazan
name: M. Heliasz
name: S. Henne
name: A. Hensen
name: O. Hermansen
name: P. Keronen
name: R. Kivi
name: K. Komínková
name: D. Kubistin
name: O. Laurent
name: T. Laurila
name: J. V. Lavric
name: I. Lehner
name: K. E. J. Lehtinen
name: A. Leskinen
name: M. Leuenberger
name: I. Levin
name: M. Lindauer
name: M. Lopez
name: C. Lund Myhre
name: I. Mammarella
name: G. Manca
name: A. Manning
name: M. V. Marek
name: P. Marklund
name: D. Martin
name: F. Meinhardt
name: N. Mihalopoulos
name: M. Mölder
name: J. A. Morgui
name: J. Necki
name: S. O'Doherty
name: C. O'Dowd
name: M. Ottosson
name: C. Philippon
name: S. Piacentino
name: J. M. Pichon
name: C. Plass-Duelmer
name: A. Resovsky
name: L. Rivier
name: X. Rodó
name: M. K. Sha
name: H. A. Scheeren
name: D. Sferlazzo
name: T. G. Spain
name: K. M. Stanley
name: M. Steinbacher
name: P. Trisolino
name: A. Vermeulen
name: G. Vítková
name: D. Weyrauch
name: I. Xueref-Remy
name: K. Yala
name: C. Yver Kwok
Publisher: name: The Royal Society
Year: 2020
Subjects: Environmental Science

description: 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<sub>2</sub>) 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<sub>2</sub> seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing to investigate how ecosystem flux anomalies impacted spatial CO<sub>2</sub> 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<sub>2</sub> 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<sub>2</sub> 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<sub>2</sub> transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO<sub>2</sub> 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<sub>2</sub> anomaly observed in 2018 were compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO<sub>2</sub> 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'.