Browsing by Author "Chevallier, Frederic"

Now showing 1 - 3 of 3

Drought rapidly diminishes the large net CO2 uptake in 2011 over semi-arid Australia
(2016-11) ma, Xuanlong; Huete, Alfredo; Cleverly, James; Eamus, Derek; Chevallier, Frederic; Joiner, Joanna; Poulter, Benjamin; Zhang, Yongguang; Guanter, Luis; Meyer, Wayne; Xie, Zunyi; Ponce-Campos, Guillermo
Each year, terrestrial ecosystems absorb more than a quarter of the anthropogenic carbon emissions, termed as land carbon sink. An exceptionally large land carbon sink anomaly was recorded in 2011, of which more than half was attributed to Australia. However, the persistence and spatially attribution of this carbon sink remain largely unknown. Here we conducted an observation-based study to characterize the Australian land carbon sink through the novel coupling of satellite retrievals of atmospheric CO2 and photosynthesis and in-situ flux tower measures. We show the 2010-11 carbon sink was primarily ascribed to savannas and grasslands. When all biomes were normalized by rainfall, shrublands however, were most efficient in absorbing carbon. We found the 2010-11 net CO2 uptake was highly transient with rapid dissipation through drought. The size of the 2010-11 carbon sink over Australia (0.97 Pg) was reduced to 0.48 Pg in 2011-12, and was nearly eliminated in 2012-13 (0.08 Pg). We further report evidence of an earlier 2000-01 large net CO2 uptake, demonstrating a repetitive nature of this land carbon sink. Given a significant increasing trend in extreme wet year precipitation over Australia, we suggest that carbon sink episodes will exert greater future impacts on global carbon cycle.
Land use change and El Niño-Southern Oscillation drive decadal carbon balance shifts in Southeast Asia
(2018-03) Kondo, Masayuki; Ichii, Kazuhito; Patra, Prabir K.; Canadell, Joseph G.; Poulter, Benjamin; Stitch, Stephen; Calle, Leonardo; Liu, Yi Y.; van Dijk, Albert I. J. M.; Saeki, Tazu; Saigusa, Nobuko; Friedlingstein, Pierre; Arneth, Almut; Harper, Anna B.; Jain, Atul K.; Kato, Etsushi; Koven, Charles D.; Li, Fang; Pugh, Thomas A. M.; Zaehle, Sonke; Wiltshire, Andy; Chevallier, Frederic; Maki, Takashi; Nakamura, Takashi; Niwa, Yosuke; Rödenbeck, Christian
An integrated understanding of the biogeochemical consequences of climate extremes and land use changes is needed to constrain land-surface feedbacks to atmospheric CO2 from associated climate change. Past assessments of the global carbon balance have shown particularly high uncertainty in Southeast Asia. Here, we use a combination of model ensembles to show that intensified land use change made Southeast Asia a strong source of CO2 from the 1980s to 1990s, whereas the region was close to carbon neutral in the 2000s due to an enhanced CO2 fertilization effect and absence of moderate-to-strong El Niño events. Our findings suggest that despite ongoing deforestation, CO2 emissions were substantially decreased during the 2000s, largely owing to milder climate that restores photosynthetic capacity and suppresses peat and deforestation fire emissions. The occurrence of strong El Niño events after 2009 suggests that the region has returned to conditions of increased vulnerability of carbon stocks.
On the ability of a global atmospheric inversion to constrain variations of CO2 fluxes over Amazonia
(2015-01) Molina, L.; Broquet, G.; Imbach, P.; Chevallier, Frederic; Poulter, Benjamin; Bonal, D.; Burban, B.; Ramonet, M.; Gatti, L. V.; Wofsy, Steven C.; Munger, J. William; Dlugokencky, E.; Ciais, Philippe
The exchanges of carbon, water, and energy between the atmosphere and the Amazon Basin have global implications for current and future climate. Here, the global atmospheric inversion system of the Monitoring of Atmospheric Composition and Climate service (MACC) was used to further study the seasonal and interannual variations of biogenic CO2 fluxes in Amazonia. The system assimilated surface measurements of atmospheric CO2 mole fractions made over more than 100 sites over the globe into an atmospheric transport model. This study added four surface stations located in tropical South America, a region poorly covered by CO2 observations. The estimates of net ecosystem exchange (NEE) optimized by the inversion were compared to independent estimates of NEE upscaled from eddy-covariance flux measurements in Amazonia, and against reports on the seasonal and interannual variations of the land sink in South America from the scientific literature. We focused on the impact of the interannual variation of the strong droughts in 2005 and 2010 (due to severe and longer-than-usual dry seasons), and of the extreme rainfall conditions registered in 2009. The spatial variations of the seasonal and interannual variability of optimized NEE were also investigated. While the inversion supported the assumption of strong spatial heterogeneity of these variations, the results revealed critical limitations that prevent global inversion frameworks from capturing the data-driven seasonal patterns of fluxes across Amazonia. In particular, it highlighted issues due to the configuration of the observation network in South America and the lack of continuity of the measurements. However, some robust patterns from the inversion seemed consistent with the abnormal moisture conditions in 2009.