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| Titel |
Modelling bulk surface resistance from MODIS time series data to estimate actual regional evapotranspiration |
| VerfasserIn |
Dario Autovino, Mario Minacapilli, Giuseppe Provenzano |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103479
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| Publikation (Nr.) |
 EGU/EGU2015-2889.pdf |
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| Zusammenfassung |
| Estimation of actual evapotraspiration by means of Penman-Monteith (P-M) equation
requires the knowledge of the so-called “bulk surface resistance”, rc,act, representing the
vapour flow resistance through the transpiring crop and evaporating soil surface. The
accurate parameterization of rc,act still represents an unexploited topic, especially
in the case of heterogeneous land surface. In agro-hydrological applications, the
P-M equation commonly used to evaluate reference evapotranspiration (ET0) of
a well-watered “standardized crop” (grass or alfalfa), generally assumes for the
bulk surface resistance a value of 70 s m-1. Moreover, specific crop coefficients
have to be used to estimate maximum and/or actual evapotranspiration based on
ET0.
In this paper, a simple procedure for the indirect estimation of rc,act as function of a
vegetation index computed from remote acquisition of Land Surface Temperature (LST), is
proposed.
An application was carried out in an irrigation district located near Castelvetrano, in
South-West of Sicily, mainly cultivated with olive groves, in which actual evapotranspiration
fluxes were measured during two years (2010-2011) by an Eddy Covariance flux tower (EC).
Evapotranspiration measurements allowed evaluating rc,actbased on the numerical inversion
of the P-M equation. In the same study area, a large time series of MODIS LST data,
characterized by a spatial resolution of 1x1 km and a time step of 8-days, was also acquired
for the period from 2000 to 2014.
A simple Vegetation Index Temperatures (VTI), with values ranging from 0 to 1, was
computed using normalized LST values. Evapotranspiration fluxes measured in 2010 were
used to calibrate the relationship between rc,act and VTI, whereas data from 2011 were used
for its validation.
The preliminary results evidenced that, for the considered crop, an almost constant value
of rc,act, corresponding to about 250 s m-1, can be considered typical of periods in which the
crop is well-watered and VTIs are lower than 0.5 (from September to mid-April)
whereas, during dry periods the values of rc,act increased exponentially with VTI, until
reaching a maximum of about 1100 s m-1, corresponding approximately to a VTI of
0.98.
Using estimated values of rc,actin the P-M equation made it possible to identify the
seasonal trend of actual evapotranspiration, with errors of about 0.5 mm d-1. The
proposed approach can be suggested for estimating crop water requirements at
regional scale and, potentially, as a tool to manage water resources in agriculture. |
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