The fingerprint of the summer 2018 drought in Europe on ground-based atmospheric CO2 measurements

During the summer of 2018 a widespread drought developed over Northern and Central Europe. The significant increase in temperature and the reduction of soil moisture have influenced the carbon dioxide (CO2 ) exchanges between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in auto- and heterotrophic respiration, or allowing more frequent and/or stronger fires, which were particularly important in Sweden at the end of July 2018. In this study we characterise the resulting perturbation of the atmospheric CO2 seasonal cycles. The year 2018 has an excellent coverage of the European regions affected by drought, allowing to investigate how large-scale ecosystem flux anomalies impacted spatial CO2 gradients between stations in 2018. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the dense Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO2 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 CO2 mole fraction 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 CO2 transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO2 uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration legated from the previous summer. For stations with sufficiently long time series, the amplitudes of the CO2 anomaly observed in 2018 were compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies during these years, we found a higher CO2 anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018.

RAMONET Michel;  CIAIS Philippe;  APADULA Francesco;  BARTYZEL Jakub;  BASTOS Ana;  BERGAMASCHI Peter;  BRUNNER D.;  CARACCIOLO DI TORCHIARO Luigi;  CALZOLARI Francescopiero;  CHEN Huilin;  CHMURA Lukasz;  COLOMB Aurelie;  CONIL Sébastien;  CRISTOFANELLI Paolo;  CUEVAS-AGULLÓ Emilio;  CURCOLL Roger;  DELMOTTE Marc;  DI SARRA Alcide;  EMMENEGGER Lukas;  FORSTER Grant;  FRUMAU A;  GERBIG Christoph;  GHEUSI François;  HAMMER Samuel;  HASZPRA L.;  HATAKKA Juha;  HAZAN Lynn;  HELIASZ Michal;  HENNE S;  HENSEN A;  HERMANSEN Ove;  KERONEN P.;  KIVI R.;  KOMINKOVA Kateřina;  KUBISTIN Dagmar;  LAURENT Olivier;  LAURILA T;  LAVRIC Jost Valentin;  LEHNER Irene;  LEHTINEN K.E.J.;  LESKINEN Ari;  LEUENBERGER Markus;  LEVIN Ingeborg;  LINDAUER Matthias;  LOPEZ Morgan;  LUND MYHRE Catherine;  MAMMARELLA Ivan;  MANCA Giovanni;  MANNING A.;  MAREK Michal;  MARKLUND Per;  MARTIN Damien;  MEINHARDT Frank;  MIHALOPOULOS Nikos;  MOLDER Meelis;  MORGUI Josep Anton;  NECKI J.;  O'DOHERTY S.;  O'DOWD C.;  OTTOSSON Mikaell;  PHILIPPON Carole;  PIACENTINO S.;  PICHON Jean-Marc;  PLASS-DUELMER C.;  RESOVSKY Alex;  RIVIER L.;  RODO Xavier;  SHA Kumar Mahesh;  SCHEEREN Hubertus A.;  SFERLAZZO Damiano;  SPAIN Gerard T.;  STANLEY Kieran;  STEINBACHER M.;  TRISOLINO Pamela;  VERMEULEN Alex;  VITKOVA Gabriela;  WEYRAUCH Dietmar;  XUEREF-REMY Irene;  YALA Khalil;  YVER C.; 

2020-10-07

ROYAL SOC

JRC119209

0962-8436 (online),   

https://publications.jrc.ec.europa.eu/repository/handle/JRC119209,   

10.1098/rstb.2019.0513 (online),