Eddy covariance measurements in Sahelian semi-arid savanna

Monitoring the changes in ecosystem functioning is pivotal for
understanding the global carbon cycle. Despite its size and contribution
to the global carbon cycle, Africa is largely understudied in regard to
ongoing changes in its ecosystem functioning and their responses to
climate change. One of the reasons is the lack of long-term in situ data.
Here, we use eddy covariance to quantify the net ecosystem exchange (NEE)
and its components—gross primary production (GPP) and ecosystem
respiration (Reco) for years 2010–2022 for a Sahelian semiarid savanna to
study trends in the fluxes. Significant negative trends were found for NEE
(12.7 ± 2.8 g C m2 year−1), GPP (39.6 ± 7.9 g C m2 year−1),
and Reco (32.2 ± 8.9 g C m2 year−1). We found that NEE
decreased by 60% over the study period, and this decrease was mainly
caused by stronger negative trends in rainy season GPP than
in Reco. Additionally, we observed strong increasing trends in
vapor pressure deficit, but no trends in rainfall or soil water content.
Thus, a proposed explanation for the decrease in carbon sink strength is
increasing atmospheric dryness. The warming climate in the Sahel, coupled
with increasing evaporative demand, may thus lead to decreased GPP levels
across this biome, and lowering its CO2 sequestration.