Analysis of evaporative fraction diurnal behaviour

Gentine, Pierre; Entekhabi, Dara; Chehbouni, Abdelghani; Boulet, G.; Duchemin, B.

doi:10.1016/j.agrformet.2006.11.002

Cited by 272 publications

(215 citation statements)

References 50 publications

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“…Again, this is legitimate for the parallel version, but for the series version one must inquire whether local advection effects do not enhance latent heat flux values over the total potential value of a uniformly wet surface. No calibration is performed, the minimum stomatal resistance value is arbitrarily set to a realistic level for herbaceous vegetation (100 s m −1 , Gentine et al, 2007) and the G / Rn s ratio ξ is set to 40 % (a value often encountered Figure 6. Scatterplot of retrieved vs. observed latent heat flux at midday at the rainfed wheat site.…”

Section: Evapotranspiration Estimatesmentioning

confidence: 99%

The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

Boulet

Mougenot

Lhomme

et al. 2015

Hydrol. Earth Syst. Sci.

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Abstract.Evapotranspiration is an important component of the water cycle, especially in semi-arid lands. A way to quantify the spatial distribution of evapotranspiration and water stress from remote-sensing data is to exploit the available surface temperature as a signature of the surface energy balance. Remotely sensed energy balance models enable one to estimate stress levels and, in turn, the water status of continental surfaces. Dual-source models are particularly useful since they allow derivation of a rough estimate of the water stress of the vegetation instead of that of a soil-vegetation composite. They either assume that the soil and the vegetation interact almost independently with the atmosphere (patch approach corresponding to a parallel resistance scheme) or are tightly coupled (layer approach corresponding to a series resistance scheme). The water status of both sources is solved simultaneously from a single surface temperature observation based on a realistic underlying assumption which states that, in most cases, the vegetation is unstressed, and that if the vegetation is stressed, evaporation is negligible. In the latter case, if the vegetation stress is not properly accounted for, the resulting evaporation will decrease to unrealistic levels (negative fluxes) in order to maintain the same total surface temperature. This work assesses the retrieval performances of total and component evapotranspiration as well as surface and plant water stress levels by (1) proposing a new dual-source model named Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) in two versions (parallel and series resistance networks) based on the TSEB (Two-Source Energy Balance model, Norman et al., 1995) model rationale as well as state-of-the-art formulations of turbulent and radiative exchange, (2) challenging the limits of the underlying hypothesis for those two versions through a synthetic retrieval test and (3) testing the water stress retrievals (vegetation water stress and moisture-limited soil evaporation) against in situ data over contrasted test sites (irrigated and rainfed wheat). We demonstrated with those two data sets that the SPARSE series model is more robust to component stress retrieval for this cover type, that its performance increases by using bounding relationships based on potential conditions (root mean square error lowered by up to 11 W m −2 from values of the order of 50-80 W m −2 ), and that soil evaporation retrieval is generally consistent with an independent estimate from observed soil moisture evolution.

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Section: Evapotranspiration Estimatesmentioning

confidence: 99%

The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

Boulet

Mougenot

Lhomme

et al. 2015

Hydrol. Earth Syst. Sci.

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“…Estimation of the available energy differs significantly from the SEB models. A more detailed presentation of the model is available in Gentine et al (2007).…”

Section: The Soil-vegetation-atmosphere Transfer (Svat) Modelmentioning

confidence: 99%

Intercomparison of four remote-sensing-based energy balance methods to retrieve surface evapotranspiration and water stress of irrigated fields in semi-arid climate

Chirouze

Boulet

Jarlan

et al. 2014

Hydrol. Earth Syst. Sci.

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Abstract. Instantaneous evapotranspiration rates and surface water stress levels can be deduced from remotely sensed surface temperature data through the surface energy budget. Two families of methods can be defined: the contextual methods, where stress levels are scaled on a given image between hot/dry and cool/wet pixels for a particular vegetation cover, and single-pixel methods, which evaluate latent heat as the residual of the surface energy balance for one pixel independently from the others. Four models, two contextual (S-SEBI and a modified triangle method, named VIT) and two single-pixel (TSEB, SEBS) are applied over one growing season (December-May) for a 4 km × 4 km irrigated agricultural area in the semi-arid northern Mexico. Their performance, both at local and spatial standpoints, are compared relatively to energy balance data acquired at seven locations within the area, as well as an uncalibrated soilvegetation-atmosphere transfer (SVAT) model forced with local in situ data including observed irrigation and rainfall amounts. Stress levels are not always well retrieved by most models, but S-SEBI as well as TSEB, although slightly biased, show good performance. The drop in model performance is observed for all models when vegetation is senescent, mostly due to a poor partitioning both between turbulent fluxes and between the soil/plant components of the latent heat flux and the available energy. As expected, contextual methods perform well when contrasted soil moisture and vegetation conditions are encountered in the same image (therefore, especially in spring and early summer) while they tend to exaggerate the spread in water status in more homogeneous conditions (especially in winter). Surface energy balance models run with available remotely sensed products prove to be nearly as accurate as the uncalibrated SVAT model forced with in situ data.

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“…We calculated the EF from the daytime λEa and H values, and considered it as a direct proxy for evaporative stress (Maes et al, 2011;Gentine et al, 2007;Gentine et al, 2011a). The underlying hypothesis is that under unstressed conditions, a larger fraction of the available energy is used to evaporate.…”

Section: Selection Of Unstressed Daysmentioning

confidence: 99%

Potential evaporation at eddy-covariance sites across the globe

Maes¹,

Gentine²,

Verhoest³

et al. 2018

Preprint

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Abstract. Potential evaporation (Ep) is a crucial variable for hydrological forecast and in drought monitoring systems. However, multiple interpretations of Ep exist, and these reflect a diverse range of methods to calculateEp. As such, a comparison of the performance of these methods against field observations in different global ecosystems is badly needed. In this study, we used eddy-covariance measurements from 107 sites of the FLUXNET2015 database, covering 11 different biomes, to parameterize and compare the main Ep methods and 10 uncover their relative performance. For each site, we extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The evaporation measurements during these days were used as reference to validate the different methods to estimate Ep. Our results indicate that a simple radiation-driven method calibrated per biome consistently performed best, with a mean correlation of 0.93, an unbiased RMSE of 0.56 mm day -1, and a bias of -0.02 mm day -1 against in situ measurements of unstressed 15 evaporation. A Priestley and Taylor method, calibrated per biome, performed just slightly worse, yet substantially and consistently better than more complex Penman, Penman-Monteith-based or temperature-based approaches.We show that the poor performance of Penman-Monteith based approaches relates largely to the fact that the unstressed stomatal conductance was assumed constant. Further analysis showed that the biome-specific parameters required for the simple radiation-driven methods are relatively constant per biome. This makes this 20 simple radiation-driven method calibrated per biome a robust method that can be incorporated into models for improving our understanding of the impact of global warming on future global water use and demand, drought severity and ecosystem productivity.

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Analysis of evaporative fraction diurnal behaviour

Cited by 272 publications

References 50 publications

The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

Intercomparison of four remote-sensing-based energy balance methods to retrieve surface evapotranspiration and water stress of irrigated fields in semi-arid climate

Potential evaporation at eddy-covariance sites across the globe

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