 |
| Titel |
Performance of evapotranspiration models for a maize agro-ecosystem: from bare soil to maximum coverage in irrigated and rainfed conditions |
| VerfasserIn |
O. Gharsallah, A. Facchi, C. Gandolfi |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065873
|
|
|
|
|
|
| Zusammenfassung |
| To assure an efficient management and planning of irrigation water resources, an accurate
computation of actual evapotranspiration (ET) from cropped surfaces is needed. ET models
can be classified in two categories: “direct” methods, based on the original Penman-Monteith
(P-M) equation, in which the canopy resistance rc is modelled, and “indirect” methods, based
on the calculation of ET for a well-watered reference grass (ET0) with constant rc multiplied
by a crop coefficient that represents the relative rate of ET from a specific crop and condition
to that of the reference.
This last procedure, standardized by FAO-56 bulletin, is the most widely adopted for the
estimation of ET. However, in literature there are evidences that direct methods (P-M models
with rc modelled) are still the most performing. In fact, for indirect methods, errors
introduced by the calculation of ET0considering a constant rc for reference crop and by the
estimation of the crop coefficient, which actually integrates several physical and biological
factors, can be relevant.
This study evaluates the performance of different models for the estimation of ET for a
maize agro-ecosystem in the Padana Plain (Northern Italy). The following models have been
considered: 1) the “one-step” P-M model using a constant daily canopy resistance following
the classical Monteith approach; 2) the “one-step” P-M model using a variable canopy
resistance based on the approach of Katerji-Perrier, in which rc is calculated as a function of
climate variables, aerodynamic resistance, vegetation type and its water status; 3) the
“two-step” Shuttleworth model as updated by Shuttleworth and Gurney (1990), which
combines one-dimensional models of crop transpiration and of soil evaporation,
where canopy and soil surface resistances regulate the heat and mass transfer at the
plant and soil surfaces, and aerodynamic resistances regulate those between these
surfaces and the atmospheric boundary layer; 5) the indirect “single crop coefficient”
method proposed by FAO-56; 6) the indirect “double crop coefficient” method
proposed by FAO-56, which allows the separation of soil evaporation and crop
transpiration.
Latent heat fluxes measured in 2006, 2010 and 2011 in an experimental maize field by
eddy-covariance are used to evaluate the models accuracy. Crop, soil and meteo data
monitored contextually are used for different models implementation. Data from the closest
standard agro-meteorological station are adopted in the ET0 calculation for indirect
methods.
Results of this work confirm what reported by other authors in the literature,
demonstrating that the calculation of crop evapotranspiration by direct method is more
accurate than the use of indirect methods for both irrigated (2006, 2010) and rainfed (2011)
conditions. |
|
|
|
|
|
|