%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Allies, A.
%A Demarty, Jérome
%A Olioso, A.
%A Moussa, I. B.
%A Issoufou, H. B. A.
%A Velluet, Cecile
%A Bahir, M.
%A Mainassara, I.
%A Oi, Monique
%A Chazarin, Jean-Philippe
%A Cappelaere, Bernard
%T Evapotranspiration estimation in the Sahel using a new ensemble-contextual method
%D 2020
%L fdi:010077972
%G ENG
%J Remote Sensing
%K evapotranspiration mapping ; contextual approach ; Sahel ; MODIS ; southwest Niger
%K NIGER ; ZONE SAHELIENNE
%M ISI:000515393800039
%N 3
%P art. 380 [34 ]
%R 10.3390/rs12030380
%U https://www.documentation.ird.fr/hor/fdi:010077972
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers20-04/010077972.pdf
%V 12
%W Horizon (IRD)
%X In many tropical areas, evapotranspiration is the most important but least known component of the water cycle. An innovative method, named E3S (for EVASPA S-SEBI Sahel), was developed to provide spatially-distributed estimates of daily actual evapotranspiration (ETd) from remote sensing data in the Sahel. This new method combines the strengths of a contextual approach that is used to estimate the evaporative fraction (EF) from surface temperature vs. albedo scatterograms and of an ensemble approach that derives ETd estimates from a weighted average of evapotranspiration estimated from several EF methods. In this work, the two combined approaches were derived from the simplified surface energy balance index (S-SEBI) model and the EVapotranspiration Assessment from SPAce (EVASPA) tool. Main innovative aspects concern (i) ensemble predictions of ETd through the implementation of a dynamic weighting scheme of several evapotranspiration estimations, (ii) epistemic uncertainty of the estimation of ETd from the analysis of the variability of evapotranspiration estimates, and (iii) a new cloud filtering method that significantly improves the detection of cloud edges that negatively affect EF determination. E3S was applied to MODIS/TERRA and AQUA datasets acquired during the 2005-2008 period over the mesoscale AMMA-CATCH (Analyse Multidisciplinaire de la Mousson Africaine-Couplage de l'Atmosphere Tropicale et du Cycle Hydrologique) observatory in South-West Niger. E3S estimates of instantaneous and daily available energy, evaporative fraction, and evapotranspiration were evaluated at a local scale based on two field-monitored plots representing the two main ecosystem types in the area-a millet crop and a fallow savannah bush. In addition to these ground-based observations, the local scale evaluation was performed against continuous simulations by a locally-calibrated soil-vegetation-atmosphere transfer model for the two plots. The RMSE (root mean square error) from this comparison for E3S's ETd estimates from combined AQUA/TERRA sources was 0.5 mmday(-1), and the determination coefficient was 0.90. E3S significantly improved representation of the evapotranspiration seasonality, compared with a classical implementation of S-SEBI or with the original EVASPA's non-weighted ensemble scheme. At the mesoscale, ETd estimates were obtained with an average epistemic uncertainty of 0.4 mmday(-1). Comparisons with the reference 0.25 degrees-resolution GLEAM (global land evaporation Amsterdam model) product showed good agreement. These results suggested that E3S could be used to produce reliable continuous regional estimations at a kilometric resolution, consistent with land and water management requirements in the Sahel. Moreover, all these innovations could be easily transposed to other contextual approaches.
%$ 126 ; 072