Modelling evapotranspiration of six irrigated crops under
Mediterranean climate conditions
Nader Katerji
a
, Gianfranco Rana
b,
*
a
INRA, Unite
´
de Recherche ‘‘Environnement et Grandes Cultures’’, 78850 Thiverval-Grignon, France
b
CRA, Istituto Sperimentale Agronomico, via C. Ulpiani 5, 70125 Bari, Italy
Received 30 June 2005; received in revised form 28 March 2006; accepted 13 April 2006
Abstract
Two models based on the Penman–Monteith equation have been used to calculate the evapotranspiration, on hourly and daily
scales, for six crops (grass, tomato, soybean, sunflower, grain sorghum, sweet sorghum), grown in a Mediterranean region, in well
watered conditions. These crops presented different sensitivity to the air vapour pressure deficit, due to their height ranging between
0.1 and 2.8 m. In the first model (model 1), the canopy resistance was considered variable and modelled as function of climatic
variables. The experimental tests showed that this model simulated well the evapotranspiration for the six crops, both at hourly and
daily scales. On the other hand, the simulations obtained by this model 1 at daily scale are clearly more accurate than those obtained
by using the standard FAO 56 method. In the second model (model 2), the canopy resistance, locally determined, is considered
constant. The experiments showed that the model 2 simulated acceptably the evapotranspiration only for the short crops: the grass
(at hourly and daily scales) and the tomato (only at daily scale), but with lower performances than the model 1. For the other four
crops (soybean, sunflower, grain sorghum and sweet sorghum) the model 2 seems to be not adapted to calculate correctly the
evapotranspiration. In the conclusions we discuss the advantages linked to the use of the model 1 for the direct calculation of the
evapotranspiration.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Fixed canopy resistance; Variable canopy resistance; Height crop; Penman–Monteith formulation; Vapour pressure deficit;
Aerodynamic resistance
1. Introduction
In Mediterranean regions irrigation is the only means
of producing both high and stable crop yields. Due to
the limited water resources in this region, both accurate
and available determination of the crop water require-
ments is nowadays a needed condition to maintain
efficient irrigated agriculture (Hamdy and Lacirignola,
1999). Moreover, for correct irrigation scheduling it is
necessary to know the quantity of water losses by a crop
due to evapotranspiration.
The evapotranspiration (E) of an irrigated crop can be
calculated directly by using the Penman–Monteith
formula (Monteith, 1965) with a specific value of the
crop resistance parameter and the meteorological
variables measured near/above the canopy. In practice,
the use of this formulation needs, for each species,
specific modelling of the canopy resistance (r
c
)in
relation to the environmental variables (Jarvis, 1976;
Katerji and Perrier, 1983; Jarvis and McNaughton, 1986;
Stewart, 1988).On the other hand, for crops only partially
covering the soil a correction of the resistance r
c
is
necessary in the case of non-irrigated crops, to take into
account the soil evaporation (i.a. Katerji and Perrier,
www.elsevier.com/locate/agrformet
Agricultural and Forest Meteorology 138 (2006) 142–155
* Corresponding author. Tel.: +39 080 5475026;
fax: +39 080 5475023.
E-mail addresses: katerji@bcgn.grignon.inra.fr (N. Katerji),
g_rana@libero.it (G. Rana).
0168-1923/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.agrformet.2006.04.006