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. # Eddy covariance measurements in Sahelian semi-arid savanna [Eddy covariance measurement…](Eddy covariance measurement…) ## Description of the data and file structure The CO2 flux data and evapotranspiration were collected using CPEC200 system, installed in Dahra, Senegal semi-arid savanna field site. It is one of the very few eddy covariance systems on the African continent. On top of the CO2 flux data, other environmental variables were measured: air and soil temperature, soil moisture, normalized difference vegetation index, precipitation, photosynthetically active radiation, and relative humidity. This data includes the years 2010-2022. ### Files and variables #### File: ECDahra.xlsx **Description:** Data contains half-hourly means and sums of CO2 fluxes (NEE - net ecosystem exchange; GPP - gross primary production; Reco - ecosystem respiration) and environmental variables. #N/A values represent missing CO2 flux values. ##### Variables * Column A - Index * Column B - Year * Column C - Day of Year * Column D - Half-hour of measurement * Column E - Hour of measurement * Column F - Half-hour displayed as consecutive integer * Column G - Month of measurement * Column H - Week of measurement * Column I - Measured NEE [µmol CO2 m-2 s-1] * Column J - Measured GPP [µmol CO2 m-2 s-1] * Column K - Measured Reco [µmol CO2 m-2 s-1] * Column L - Reco gap-filled in ReddyProc [µmol CO2 m-2 s-1] * Column M - Epoch Time * Column N - Average air temperature [degree Celsius] * Column O  - Average vapor pressure deficit [hPa] * Column P - Average soil moisture measured at 5 cm depth [%] * Column Q - Average soil moisture measured at 10 cm depth [%] * Column R - Average relative humidity [%] * Column S - Sum of precipitation [mm] * Column T - Average soil temperature [degree Celsius] * Column U - Average photosynthetically active radiation [µmol m-2 s-1] * Column V - Daily mean normalized difference vegetation index [-] * Column W - Time * Column X - NEE predicted by Random Forest [µmol CO2 m-2 s-1] * Column Y - GPP predicted by Random Forest [µmol CO2 m-2 s-1] * Column Z - Reco predicted by Random Forest [µmol CO2 m-2 s-1] * Column AA - Gap-filled NEE [µmol CO2 m-2 s-1] * Column AB - Gap-filled GPP [µmol CO2 m-2 s-1] * Column AC - Gap-filled Reco [µmol CO2 m-2 s-1] * Column AD - NEE [g C m-2 30min-1]  * Column AE - GPP [g C m-2 30min-1]  * Column AF - Reco [g C m-2 30min-1]  * Column AG - Record number * Column AH - Season (dry or rainy) * Column AI - Evapotranspiration [mm] * Column AJ - Water use efficiency [g C kg-1 H2O] * Column AK - Inherent water use efficiency [g C hPa kg-1 H2O]