Abstract
3-hourly Net Ecosystem Exchange (NEE) is estimated at spatial scales of 0.25 degrees over the European continent, based on the pre-operational inverse modelling framework CarboScope Regional (CSR) for the years 2006 to 2019. To assess the uncertainty originating from the choice of a-priori flux models and observational data, ensembles of inversions were produced using three terrestrial ecosystem flux models, two ocean flux models, and three sets of atmospheric stations. We find that the station set ensemble accounts for 61 % of the total spread of the annually aggregated fluxes over the full domain when varying all these elements, while the biosphere and ocean ensembles resulted in much smaller contributions to the spread of 28 % and 11 %, respectively. These percentages differ over the specific regions of Europe, based on the availability of atmospheric data. For example, the spread of the biosphere ensemble is prone to be larger in regions that are less constrained by CO2 measurements. We further investigate the unprecedented increase of temperature and simultaneous reduction of Soil Water Content (SWC) observed in 2018 and 2019. We find that NEE estimates during these two years suggest an impact of drought occurrences represented by the reduction of Net Primary Productivity (NPP), which in turn lead to less CO2 uptake across Europe in 2018 and 2019, resulting in anomalies up to 0.13 and 0.07 PgC yr-1 above the climatological mean, respectively. Annual temperature anomalies also exceeded the climatological mean by 0.46 °C in 2018 and by 0.56 °C in 2019, while standardized-precipitation-evaporation-index (SPEI) anomalies declined to −0.20 and −0.05 SPEI units below the climatological mean in both 2018 and 2019, respectively. Therefore, the biogenic fluxes showed a weaker sink of CO2 in both 2018 and 2019 (−0.22±0.05 and −0.28±0.06 PgC yr-1, respectively) in comparison with the mean −0.36±0.07 PgC yr-1 calculated over the full analysed period (i.e., fourteen years). These translate into a continental-wide reduction of the annual sink by 39 % and 22 %, respectively, larger than the typical year-to-year standard deviation of 19 % observed over the full period.
Highlights
The atmospheric mole fractions of Greenhouse Gases (GHGs) like CO2, CH4, and N2O have drastically increased since the industrial era began (Friedlingstein et al, 2019), primarily caused by anthropogenic GHG emissions
We find that the station set ensemble accounts for 61% of the total spread of the annually aggregated fluxes over the full domain when varying all these elements, while the biosphere and ocean ensembles resulted in much smaller contributions to the spread of 28% and 11%, respectively
We find that Net Ecosystem Exchange (NEE) estimates during these two years suggest an impact of drought occurrences represented by the reduction of Net Primary Productivity (NPP), which in turn lead to less CO2 uptake across Europe in 2018 and 2019, resulting in anomalies up to 0.13 and 0.07 PgC yr-1 above the climatological mean, respectively
Summary
The atmospheric mole fractions of Greenhouse Gases (GHGs) like CO2, CH4, and N2O have drastically increased since the industrial era began (Friedlingstein et al, 2019), primarily caused by anthropogenic GHG emissions. We 65 discuss the interannual variability (IAV) over this period, with special focus on the changes of NEE in 2018 and 2019, in light of the water availability and temperature variations that occurred in the wake of anomalously warm and dry conditions over the continent. These changes are analysed using the seasonal and annual NEE fluxes aggregated over different subregions in Europe.
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