Spring enhancement and summer reduction in carbon uptake during the 2018 drought in northwestern Europe

Naomi E. Smith (1) , Linda M.J. Kooijmans (1) , Gerbrand Koren (1) , Erik van Schaik (1) , Auke M. van Der Woude (1, 2) , Niko Wanders (3) , Michel Ramonet (4, 5) , Irène Xueref-Remy (6) , Lukas Siebicke (7) , Giovanni Manca (8) , Christian Brümmer (9) , Ian T. Baker (10) , Katherine D. Haynes (10) , Ingrid T. Luijkx (1) , Wouter Peters (1, 2)

1 Meteorology and Air Quality, Wageningen University and Research
2 Centre for Isotope Research, University of Groningen
3 Department of Physical Geography, Faculty of Geosciences
4 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
5 ICOS-RAMCES - ICOS-RAMCES
6 IMBE - Institut méditerranéen de biodiversité et d'écologie marine et continentale
7 University of Göttingen, Bioclimatology
8 JRC - European Commission - Joint Research Centre [Ispra]
9 Thünen Institute of Climate-Smart Agriculture
10 Department of Atmospheric Science [Fort Collins]

We analysed gross primary productivity (GPP), total ecosystem respiration (TER) and the resulting net ecosystem exchange (NEE) of carbon dioxide (CO2) by the terrestrial biosphere during the summer of 2018 through observed changes across the Integrated Carbon Observation System (ICOS) network, through biosphere and inverse modelling, and through remote sensing. Highly correlated yet independently-derived reductions in productivity from sun-induced fluorescence, vegetative near-infrared reflectance, and GPP simulated by the Simple Biosphere model version 4 (SiB4) suggest a 130–340 TgC GPP reduction in July–August–September (JAS) of 2018. This occurs over an area of 1.6 × 106 km2 with anomalously low precipitation in northwestern and central Europe. In this drought-affected area, reduced GPP, TER, NEE and soil moisture at ICOS ecosystem sites are reproduced satisfactorily by the SiB4 model. We found that, in contrast to the preceding 5 years, low soil moisture is the main stress factor across the affected area. SiB4’s NEE reduction by 57 TgC for JAS coincides with anomalously high atmospheric CO2 observations in 2018, and this is closely matched by the NEE anomaly derived by CarbonTracker Europe (52 to 83 TgC). Increased NEE during the spring (May–June) of 2018 (SiB4 −52 TgC; CTE −46 to −55 TgC) largely offset this loss, as ecosystems took advantage of favourable growth conditions.

Keywords: drought; remote sensing; European carbon balance; CO2; data assimilation

Domains: Environmental Sciences

Naomi E. Smith, Linda M.J. Kooijmans, Gerbrand Koren, Erik van Schaik, Auke M. van Der Woude, et al.. Spring enhancement and summer reduction in carbon uptake during the 2018 drought in northwestern Europe. Philosophical Transactions of the Royal Society B: Biological Sciences, 2020, 375 (1810), pp.20190509. ⟨10.1098/rstb.2019.0509⟩. ⟨hal-02937274⟩