The fingerprint of the summer 2018 drought in Europe on ground-based atmospheric CO₂measurements

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'.

A historical, geographical and ecological perspective on the 2018 European summer drought

“…In this special issue, we provide a synthesis of studies ranging from in situ to continental scales, from in situ monitoring to large-scale remote sensing and to atmospheric and surface modelling to address these questions. Based on dense atmospheric CO 2 mole fraction measurements in Europe, Ramonet et al [38] show that CO 2 concentrations were above the previous years' values during July and August over most of Europe, especially in Central Europe and Scandinavia, but they also point to lower CO 2 mole fractions during spring (May and June). These measurements have large surface flux sensitivity footprints [39] and suggest an increased spring CO 2 sink, followed by a reduction of this sink in summer.…”

An algorithm to detect non-background signals in greenhouse gas time series from European tall tower and mountain stations

“…For the 90day application, we concentrate on the extended summer growing season (April-October) to examine the capacities of the methodology in detecting large-scale terrestrial biosphere anomalies. We focus in particular on the summer of 2018, which saw a spate of intense droughts and heat waves across Central and Northern Europe that altered continent-wide GPP and CO2 storage and flux patterns (Lindroth et al, 2020;Ramonet et al, 2020;Rinne et al, 2020;Wang et al, 2020). Table 2 summarizes the results of the SSA extraction for the ten sites for the period 1 November 2015 to 31 March 2020.…”

“…Figure 8 shows the 90-day extraction procedure at each of the ten sites and is analogous to Fig. 4, except that we show the period 1 January 2018 to 1 January 2019, as we wish to assess the algorithm's performance with regard to the timing, intensity and extent of the 2018 drought and heat wave events across Central and Northern Europe (Ramonet et al, 2020). Figure 9 https://doi.org/10.5194/amt-2021-16 Preprint.…”

Cézeaux-Aulnat-Opme-Puy De Dôme: a multi-site for the long-term survey of the tropospheric composition and climate change

“…Greenhouse gas (CO 2 , CH 4 , N 2 O, and SF 6 ) measurements in November 2000 were part of the SNO-RAMCES/ICOS-France French monitoring program (Broquet et al, 2013;Lopez et al, 2015;Ramonet et al, 2010;Sturm et al, 2005). Three types of analyzers were used: non-dispersive infrared instruments (NDIR, LICOR-6251 from 7 November 2000 to 20 November 2007; LICOR-6252 from 21 November 2007 to 3 April 2011); gas chromatography (GC, Agilent HP-6890N from July 2010 to April 2015); and cavity ringdown spectrometers (CRDS) commercialized by PICARRO (G1301/no.…”

“…Radionuclide measurements are used to determine the boundary layer/free tropospheric conditions (Farah et al, 2018). The CO 2 surface fluxes are estimated and revealed a clear seasonal cycle, under the influence of plant assimilation, and burning of fossil fuel (Lopez et al, 2015;Ramonet et al, 2020). According to Lopez et al (2015), the measurements observed at PUY during the night are representative of the central part of France, mostly west of the station.…”