Abstract. In the last decades terrestrial ecosystems have
reabsorbed on average more than one-quarter of anthropogenic emissions
(Le
Quéré et al., 2018). However, this large carbon sink is modulated by
climate and is therefore highly variable in time and space. The magnitude
and temporal changes in the sensitivity of terrestrial CO2 fluxes to
climate drivers are key factors to determine future atmospheric CO2
concentration and climate trajectories. In the literature, there is so far a
strong focus on the climatic controls of daily and long-term variability,
while less is known about the key drivers at a seasonal timescale and about
their variation over time (Wohlfahrt
et al., 2008). This latter temporal scale is relevant to assess which
climatic drivers dominate the seasonality of the fluxes and to understand
which factors limit the CO2 exchange during the course of the year.
Here, we investigate the global sensitivity of net terrestrial CO2
fluxes, derived from atmospheric inversion, to three key climate drivers
(i.e. global radiation and temperature from WFDEI and soil water content from
ERA-Interim) from weekly to seasonal temporal scales, in order to explore
the short-term interdependence between climate and the terrestrial carbon
budget. We observed that the CO2 exchange is controlled by temperature
during the carbon uptake period over most of the land surface (from 55 % to
52 % of the total surface), while radiation is the most widespread
dominant climate driver during the carbon release period (from 64 % to 70 %
of the total surface). As expected, soil water content plays a key role in
arid regions of the Southern Hemisphere during both the carbon uptake and
the carbon release period. Looking at the decadal trend of these
sensitivities (1985–2016) we observed that the importance of radiation as a
driver is increasing over time, while we observed a decrease in sensitivity
to temperature in Eurasia. Overall, we show that flux temporal variation due
to a specific driver has been dominated by the temporal changes in ecosystem
sensitivity (i.e. the response of ecosystem to climate) rather than to the
temporal variability of the climate driver itself over the last decades.
Ultimately, this analysis shows that the ecosystem response to climate is
significantly changing both in space and in time, with potential
repercussion on the future terrestrial CO2 sink and therefore on the
role that land may play in climate trajectories.
Soil water content effects on net ecosystem CO2 exchange and actual evapotranspiration in a Mediterranean semiarid savanna of Central Chile
