Actual evapotranspiration in drylands derived from in-situ and satellite data: Assessing biophysical constraints

Monica Garcia, Inge Sandholt, Pietro Ceccato, Marc Ridler, Eric Mougin, Laurent Kergoat, Laura Morillas, Franck Timouk, Rasmus Fensholt, Francisco Domingo

Research output: Contribution to journalJournal articleResearchpeer-review


Improving regional estimates of actual evapotranspiration (lambda E) in water-limited regions located at climatic transition zones is critical. This study assesses an lambda E model (PT-JPL model) based on downscaling potential evapotranspiration according to multiple stresses at daily time-scale in two of these regions using MSG-SEVIRI (surface temperature and albedo) and MODIS products (NDVI, LAI and f(PAR)). An open woody savanna in the Sahel (Mali) and a Mediterranean grassland (Spain) were selected as test sites with Eddy Covariance data used for evaluation. The PT-JPL model was modified to run at a daily time step and the outputs from eight algorithms differing in the input variables and also in the formulation of the biophysical constraints (stresses) were compared with the lambda E from the Eddy Covariance. Model outputs were also compared with other modeling studies at similar global chyland ecosystems.

The novelty of this paper is the computation of a key model parameter, the soil moisture constraint, relying on the concept of apparent thermal inertia (f(SM-ATI)) computed with surface temperature and albedo observations. Our results showed that f(SM-ATI) from both in-situ and satellite data produced satisfactory results for lambda E at the Sahelian savanna, comparable to parameterizations using field-measured Soil Water Content (SWC) with r(2) greater than 0.80. In the Mediterranean grasslands however, with much lower daily lambda E values, model results were not as good as in the Sahel (r(2)= 0.57-0.31) but still better than reported values from more complex models applied at the site such as the Two Source Model (TSM) or the Penman-Monteith Leuning model (PML).

PT-JPL-daily model with a soil moisture constraint based on apparent thermal inertia, f(SM-ATI) offers great potential for regionalization as no field-calibrations are required and water vapor deficit estimates, required in the original version, are not necessary, being air temperature and the available energy (Rn-G) the only input variables required, apart from routinely available satellite products. (c) 2012 Elsevier Inc. All rights reserved.
Original languageEnglish
JournalRemote Sensing of Environment
Pages (from-to)103-118
Publication statusPublished - 2013
Externally publishedYes


  • Evapotranspiration
  • Surface temperature
  • Priestley–Taylor
  • Thermal inertia
  • Water-limited ecosystems


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