Effects of simulated inundation on wetland methane flux predictions for the southeastern U.S.

textThis work provides an overview of factors that influence methane emissions from natural wetlands in the southeastern U.S. at seasonal and interannual timescales. It then examines simulations using CLM4Me, a methane biogeochemistry model run within CESM, through comparison with recently compiled flux estimations from remote sensing data. In addition, we assess how seasonal methane flux simulations in CLM4Me are affected by the use of alternative estimates of inundated land fraction. Inundation predictions are provided by DYPTOP, a TOPMODEL implementation which can be used to simulate the dynamics of wetland spatial distribution. Results may aid in future model development and in understanding the role of subtropical and temperate North American wetlands under future climate projections.Geological Science

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

We present a statistical framework to identify regional signals in station-based CO2 time series with minimal local influence. A curve-fitting function is first applied to the detrended time series to derive a harmonic describing the annual CO2 cycle. We then combine a polynomial fit to the data with a short-term residual filter to estimate the smoothed cycle and define a seasonally adjusted noise component, equal to 2 standard deviations of the smoothed cycle about the annual cycle. Spikes in the smoothed daily data which surpass this +/- 2 sigma threshold are classified as anomalies. Examining patterns of anomalous behavior across multiple sites allows us to quantify the impacts of synoptic-scale atmospheric transport events and better understand the regional carbon cycling implications of extreme seasonal occurrences such as droughts.Peer reviewe

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.JRC.C.5-Air and Climat

The fingerprint of the summer 2018 drought in Europe on ground-based atmospheric CO 2 measurements

International audienceDuring 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 (CO2) 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 CO2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing theinvestigation of how ecosystem flux anomalies impacted spatial CO2 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 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 usualsummer minimum in CO2 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 inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO2 anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas mostaffected by the temperature anomalies, 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.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’