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A Non-Stationary 1981–2012 AVHRR NDVI3g Time Series
Remote Sens. 2014, 6(9), 8923-8944; doi:10.3390/rs6098923
Article

1982–2010 Trends of Light Use Efficiency and Inherent Water Use Efficiency in African vegetation: Sensitivity to Climate and Atmospheric CO2 Concentrations

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1 Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL-CEA-CNRS-UVQS, F-91191, Gif sur Yvette, France 2 Geosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, UMR 5563 (CNRS/UPS/IRD/CNES), 14 Avenue Edouard Belin, 31400 Toulouse, France 3 Department of Ecology, Montana State University, P.O. Box 173460 Bozeman, MT 59717-3460, USA 4 Department of Ecology, College of Urban and Environmental Science, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China 5 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA 6 Max Planck Institute for Biogeochemistry, 07745 Jena, Germany 7 Department of Earth and Environment Room 449, Stone Science Building Boston University 675 Commonwealth Avenue Boston, MA 02215, USA
* Author to whom correspondence should be addressed.
Received: 29 April 2014 / Revised: 19 July 2014 / Accepted: 25 August 2014 / Published: 22 September 2014
(This article belongs to the Special Issue Monitoring Global Vegetation with AVHRR NDVI3g Data (1981-2011))
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Abstract

Light and water use by vegetation at the ecosystem level, are key components for understanding the carbon and water cycles particularly in regions with high climate variability and dry climates such as Africa. The objective of this study is to examine recent trends over the last 30 years in Light Use Efficiency (LUE) and inherent Water Use Efficiency (iWUE*) for the major biomes of Africa, including their sensitivities to climate and CO2. LUE and iWUE* trends are analyzed using a combination of NOAA-AVHRR NDVI3g and fAPAR3g, and a data-driven model of monthly evapotranspiration and Gross Primary Productivity (based on flux tower measurements and remote sensing fAPAR, yet with no flux tower data in Africa) and the ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) process-based land surface model driven by variable CO2 and two different gridded climate fields. The iWUE* data product increases by 10%–20% per decade during the 1982–2010 period over the northern savannas (due to positive trend of vegetation productivity) and the central African forest (due to positive trend of vapor pressure deficit). In contrast to the iWUE*, the LUE trends are not statistically significant. The process-based model simulations only show a positive linear trend in iWUE* and LUE over the central African forest. Additionally, factorial model simulations were conducted to attribute trends in iWUE and LUE to climate change and rising CO2 concentrations. We found that the increase of atmospheric CO2 by 52.8 ppm during the period of study explains 30%–50% of the increase in iWUE* and >90% of the LUE trend over the central African forest. The modeled iWUE* trend exhibits a high sensitivity to the climate forcing and environmental conditions, whereas the LUE trend has a smaller sensitivity to the selected climate forcing.
Keywords: inherent water use efficiency; light use efficiency; Africa; trend analysis; atmospheric CO2 effect and climate effects on vegetation inherent water use efficiency; light use efficiency; Africa; trend analysis; atmospheric CO2 effect and climate effects on vegetation
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Traore, A.K.; Ciais, P.; Vuichard, N.; MacBean, N.; Dardel, C.; Poulter, B.; Piao, S.; Fisher, J.B.; Viovy, N.; Jung, M.; Myneni, R. 1982–2010 Trends of Light Use Efficiency and Inherent Water Use Efficiency in African vegetation: Sensitivity to Climate and Atmospheric CO2 Concentrations. Remote Sens. 2014, 6, 8923-8944.

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