Spatial and temporal calibration of Hargreaves equation for calculating monthly ETo based on Penman‐Monteith method

The Penman-Monteith equation is the most common method for estimating reference crop evapotranspiration (ETo). However, this method needs full weather data, but few stations with complete weather data exist in Fars province in Iran. On the other hand, the Hargreaves equation is a simpler method for estimating ETo. In this study, using the weather data of seven synoptic stations in Fars province in Iran and seven synoptic stations outside the province, the Hargreaves equation was calibrated based on the Penman-Monteith method for every month of the year and for a yearly time step. The results indicate that different coefficients should be used for each month of year and yearly time step instead of the original coefficient of 0.0023 in the Hargreaves equation. Therefore, it is possible to estimate monthly ETo by using the calibrated coefficients of the Hargreaves equation for different regions of Fars province for each month of the year. Also, according to the geographical locations of each station and by using the GIS-assisted methods, spatial distribution maps of yearly calibrated coefficients in Fars province were prepared by the inverse distance square method. Copyright © 2007 John Wiley & Sons, Ltd.

[1]  Vijay P. Singh,et al.  Cross Comparison of Empirical Equations for Calculating Potential Evapotranspiration with Data from Switzerland , 2002 .

[2]  G. W. Snedecor.  Statistical Methods , 1964 .

[3]  Hossein Dehghanisanij,et al.  Assessment of evapotranspiration estimation models for use in semi-arid environments , 2004 .

[4]  Nan Zhongren,et al.  GIS-assisted spatially distributed modeling of the potential evapotranspiration in semi-arid climate of the Chinese Loess Plateau , 2004 .

[5]  Zohrab Samani,et al.  Estimating solar radiation and evapotranspiration using minimum climatological data , 2000 .

[6]  I. Lorite,et al.  Regional calibration of Hargreaves equation for estimating reference ET in a semiarid environment , 2006 .

[7]  V. Caselles,et al.  A simplified equation to estimate spatial reference evaporation from remote sensing-based surface temperature and local meteorological data , 2004 .

[8]  Richard G. Allen,et al.  Estimating Reference Evapotranspiration Under Inaccurate Data Conditions , 2002 .

[9]  Mohammad Saeed.  The Estimation of Evapotranspiration by Some Equations Under Hot and Arid Conditions , 1986 .

[10]  A. Martínez-cob,et al.  A wind-based qualitative calibration of the Hargreaves ET0 estimation equation in semiarid regions , 2004 .

[11]  Davar Khalili,et al.  Regional classification for dryland agriculture in southern Iran , 2002 .

[12]  George H. Hargreaves,et al.  Reference Crop Evapotranspiration from Temperature , 1985 .

[13]  Suat Irmak,et al.  Daily Grass and Alfalfa-Reference Evapotranspiration Estimates and Alfalfa-to-Grass Evapotranspiration Ratios in Florida , 2003 .

[14]  Claudio O. Stöckle,et al.  Evaluation of estimated weather data for calculating Penman-Monteith reference crop evapotranspiration , 2004, Irrigation Science.

[15]  Luis S. Pereira,et al.  Validation of the FAO methodology for computing ETo with limited data. Application to south Bulgaria , 2006 .

[16]  R. Lemeur,et al.  Evaluation of three evapotranspiration models in terms of their applicability for an arid region , 1990 .

[17]  H. R. Fooladmand,et al.  A computer model for design of microcatchment water harvesting systems for rain-fed vineyard , 2004 .

[18]  Richard G. Allen,et al.  Comparison of Reference Evapotranspiration Calculations as Part of the ASCE Standardization Effort , 2003 .

[19]  William O. Pruitt,et al.  Adaptation of the Thornthwaite scheme for estimating daily reference evapotranspiration , 2004 .

[20]  L. S. Pereira,et al.  Crop evapotranspiration : guidelines for computing crop water requirements , 1998 .

[21]  George H. Hargreaves,et al.  Defining and Using Reference Evapotranspiration , 1994 .

[22]  Pradeep Kashyap,et al.  Evaluation of evapotranspiration estimation methods and development of crop-coefficients for potato crop in a sub-humid region , 2001 .

[23]  R. G. Allen,et al.  Computation of ETo under Nonideal Conditions , 1997 .

[24]  C. Willmott.  Some Comments on the Evaluation of Model Performance , 1982 .

[25]  R. L. Snyder,et al.  An evaluation of common evapotranspiration equations , 1999, Irrigation Science.

[26]  R. G. Allen,et al.  Adjusting temperature parameters to reflect well-watered conditions , 1999 .

[27]  Devendra M. Amatya,et al.  Comparison of methods for estimating REF-ET , 1995 .

[28]  Marvin E. Jensen,et al.  Operational estimates of reference evapotranspiration , 1989 .

[29]  Terry A. Howell,et al.  Lysimetric evaluation of daily potential evapotranspiration models for grain sorghum , 1991 .