poster - International Conference of Agricultural Engineering

Monteith equation to climatic and parametric factors in a semi-arid climate for a reference
grass surface, grain sorghum and sweet sorghum in Italy. For grass, available energy and
aerodynamic resistance played a major role. For sweet sorghum, the model was most
sensitive to vapor pressure deficit. For grain sorghum under water stress, the most sensitive
term was canopy resistance. Irmak et al. (2006) calculated the sensitivity coefficient of the
standardized daily ASCE-Penman-Monteith equation in different climates of United States.
Recently, Ali et al. (2009) calculated the sensitivity coefficient of the FAO Penman-Monteith
equation under the environment of a semi-humid sub-tropic region of Bangladesh. The
results showed that the ET o estimates are most sensitive to maximum temperature, relative
humidity, sunshine duration, wind speed and minimum temperature, respectively. Estevez et
al. (2009) calculated the sensitivity coefficients of the standardized ASCE-Penman-Monteith
equation from 87 automatic weather stations in Spain. The results showed a large degree of
daily and seasonal variability, especially for temperature and relative humidity. Also, the
sensitivity of ET o to the same climatic variables showed significant differences among
locations. Sensitivity of the daily standardized ASCE equation to meteorological variables
has not yet been studied in Iran. Thus, the objective of this study was to investigate the
sensitivity of the standardized daily ASCE ET o equation to climatic variables under different
subclasses of arid and semiarid climatic conditions in Kerman province, southeast of Iran
and to derive sensitivity coefficients for each one.
2. Materials and Methods
2.1. Study area and weather data source
The study was carried out in Kerman province (Southeast of Iran), located between the
latitudes 27° and 30° N and the longitudes 55° and 58° W. Site elevations range from 400 to
2775 m above mean sea level. All agricultural productions in this area are irrigation-based.
In this region irrigation water resources are supplied mostly from groundwater and slightly
spring and Qanat. Surface irrigation is the most popular method of irrigation in this area,
however, frequent droughts have led to switch over to pressurized irrigation systems to
improve water use efficiency and prevent depletion of groundwater resources.
Meteorological data used in this analysis were obtained over 4 stations in Kerman province
from the Kerman Meteorological Department. These stations are located in different
subclasses of arid and semiarid climates of the province based on extended-De Martonne
classification (Khalili, 1997). Daily weather data were used in this study. Table 1 lists the
annual average weather data of 4 meteorological stations in Kerman province, including the
corresponding site elevations and coordinates. Average annual rainfall ranged from 61.3 mm
at Bam to 261.6 mm at Baft; the range for the annual air temperature was 14.8-25.0 °C; 31-
43 %, for relative humidity; and 0.5-1.6 m s-1 for wind speed at 2 m.
TABLE 1: Summary of weather station sites characteristics used in the study
2.2. ASCE standardized reference evapotranspiration equation
The purpose of the standardized reference ET equation and calculation procedures is to
bring commonality to the calculation of reference ET and to provide a standardized basis for
determining or transferring crop coefficients for agricultural and landscape use (ASCE-
EWRI, 2005). For the standardization, the ASCE-Penman-Monteith method was applied for
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