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| Titel |
Evaluation of land surface model simulations of evapotranspiration over a 12-year crop succession: impact of soil hydraulic and vegetation properties |
| VerfasserIn |
S. Garrigues, A. Olioso, J. C. Calvet, E. Martin, S. Lafont, S. Moulin, A. Chanzy, O. Marloie, S. Buis, V. Desfonds, N. Bertrand, D. Renard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 7 ; Nr. 19, no. 7 (2015-07-16), S.3109-3131 |
| Datensatznummer |
250120763
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| Publikation (Nr.) |
 copernicus.org/hess-19-3109-2015.pdf |
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| Zusammenfassung |
Evapotranspiration has been recognized as one of the most uncertain terms in
the surface water balance simulated by land surface models. In this study,
the SURFEX/ISBA-A-gs (Interaction Sol–Biosphere–Atmosphere) simulations of evapotranspiration are assessed at the
field scale over a 12-year Mediterranean crop succession. The model is
evaluated in its standard implementation which relies on the use of the ISBA
pedotransfer estimates of the soil properties. The originality of this work
consists in explicitly representing the succession of crop cycles and
inter-crop bare soil periods in the simulations and assessing its impact on
the dynamics of simulated and measured evapotranspiration over a long period
of time. The analysis focuses on key parameters which drive the simulation
of ET, namely the rooting depth, the soil moisture at saturation, the soil
moisture at field capacity and the soil moisture at wilting point. A
sensitivity analysis is first conducted to quantify the relative
contribution of each parameter on ET simulation over 12 years. The impact of
the estimation method used to retrieve the soil parameters (pedotransfer
function, laboratory and field methods) on ET is then analysed. The benefit
of representing the variations in time of the rooting depth and wilting
point is evaluated. Finally, the propagation of uncertainties in the soil
parameters on ET simulations is quantified through a Monte Carlo analysis
and compared with the uncertainties triggered by the mesophyll conductance
which is a key above-ground driver of the stomatal conductance.
This work shows that evapotranspiration mainly results from the soil
evaporation when it is continuously simulated over a Mediterranean crop
succession. This results in a high sensitivity of simulated
evapotranspiration to uncertainties in the soil moisture at field capacity
and the soil moisture at saturation, both of which drive the simulation of soil
evaporation. Field capacity was proved to be the most influencing parameter
on the simulation of evapotranspiration over the crop succession. The
evapotranspiration simulated with the standard surface and soil parameters
of the model is largely underestimated. The deficit in cumulative
evapotranspiration amounts to 24 % over 12 years. The bias in daily
daytime evapotranspiration is −0.24 mm day−1. The ISBA pedotransfer
estimates of the soil moisture at saturation and at wilting point are
overestimated, which explains most of the evapotranspiration underestimation.
The use of field capacity values retrieved from laboratory methods leads to
inaccurate simulation of ET due to the lack of representativeness of the
soil structure variability at the field scale. The most accurate simulation
is achieved with the average values of the soil properties derived from the
analysis of field measurements of soil moisture vertical profiles over each
crop cycle. The representation of the variations in time of the wilting
point and the maximum rooting depth over the crop succession has little
impact on the simulation performances. Finally, we show that the
uncertainties in the soil parameters can generate substantial uncertainties
in ET simulated over 12 years (the 95 % confidence interval represents
23 % of cumulative ET over 12 years). Uncertainties in the mesophyll
conductance have lower impact on ET. Measurement random errors explain a
large part of the scattering between simulations and measurements at
half-hourly timescale. The deficits in simulated ET reported in this work
are probably larger due to likely underestimation of ET by eddy-covariance
measurements. Other possible model shortcomings include the lack of
representation of soil vertical heterogeneity and root profile along with
inaccurate energy balance partitioning between the soil and the vegetation
at low leaf area index. |
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