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Lund University (2016)

Improvement of the GPP estimations for Sudan using the evaporative fraction as water stress factor

Dissegna, Maria Angela

Titre : Improvement of the GPP estimations for Sudan using the evaporative fraction as water stress factor

Auteur : Dissegna, Maria Angela

Université de soutenance : Lund University

Grade : Master thesis, 2016

Résumé
The Gross Primary Production "GPP" quantifies the amount of carbon entering an ecosystem. It is an ecosystem service since it is a source of energy for all organisms and it is estimated to reduce atmospheric CO2 in about 123 Pg C per year at the global scale. Therefore, the improvement of estimation methods at large spatial scales using tools such as remote sensing has gain relevance in the last years. The study evaluates two approaches of a Light Use Efficiency model with the aim to improve existing estimations of GPP in semi-arid areas. The tested inputs were the Fraction of Absorbed Photosynthetically Active Radiation "FAPAR" and the Enhanced Vegetation Index "EVI" used to represent the existent vegetation ; coupled with the Evaporative Fraction as a term to represent moisture availability. The two approaches were tested trough a site level comparison between the GPP estimated from the records of the Eddy covariance flux tower located in Demokeya site in Sudan and the MODIS GPP product MOD17A2.
The results show that the inclusion of the Evaporative Fraction increased the accuracy of the GPP estimations in the two approaches during the dry seasons but it underestimates of GPP during the rainy seasons. Both approaches performed significantly better compared to the existing MODIS GPP estimations (MOD17A2) and overall the use of FAPAR performed better than EVI for the case of Demokeya site

Mots clés : semi-arid regions, light use efficiency models, evaporative fraction, gross primary production, Physical Geography and Ecosystem analysis, GEM

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Page publiée le 9 janvier 2017, mise à jour le 30 janvier 2018