Paper Information

Journal:   JOURNAL OF WATER AND SOIL (AGRICULTURAL SCIENCES AND TECHNOLOGY)   MARCH-APRIL 2012 , Volume 26 , Number 1; Page(s) 236 To 250.
 
Paper: 

EVALUATION AND CALIBRATION OF DIFFERENT METHODS TO ESTIMATE REFERENCE CROP EVAPOTRANSPIRATION UNDER CLIMATIC DATA LIMITATIONS (CASE STUDY: KHORASAN RAZAVI PROVINCE)

 
 
Author(s):  DEHGHAN H.*, ALIZADEH A.
 
* DEPARTMENT OF WATER ENGINEERING, FACULTY OF AGRICULTURE, FERDOWSI UNIVERSITY OF MASHHAD
 
Abstract: 

Crop reference evapotranspiration (ETo) is an important agrometeorological parameter for water resources and hydrological studies, as well as for irrigation planning and management. There are several methods to estimate ETo, but their performance in different environments are not the same. The FAO Penman–Monteith (FAO PM) method has been considered as a universal standard method to estimate ETo for more than a decade. In some situations, using FAO PM is limited due to lack of input variables. In these cases, calculating ETo using FAO PM method with estimated variables is introduced, that has recommended by the FAO paper No.56. So, the purpose of this study is evaluating FAO PM performance to estimate ETo with missing data on wind speed, net radiation and saturation vapor pressure deficit, in Khorasan Razavi province. Empirical methods of ETo estimation including Priestley-Taylor, Hargreaves and Thornthwaite that require less input data, were calibrated for the region. Meteorological data from 10 synoptic stations in Khorasan Razavi province were collected to compare estimates of ETo using FAO PM method, by means of full and missing data. The results showed that when the net radiation and wind speed data are missing, again FAO PM Method is a good option for estimating evapotranspiration in Khorasan Razavi province, so that the RMSE value is less than 0.71 mm day-1. Also, Priestley–Taylor method is a good option to estimate ETo, when wind speed and vapor pressure deficit are missing, especially when this method was calibrated according to local conditions (RMSE=0.56 mm day-1). When only temperature data are available, adjusted Hargreaves and modified Thornthwaite methods were better options to estimate ETo than the FAO PM method, since RMSEs from these methods (0.57 and 0.63 mm day-1, respectively) were smaller than FAO PM (RMSE=0.88 mm day-1).

 
Keyword(s): CROP REFERENCE EVAPOTRANSPIRATION, PRIESTLEY-TAYLOR, HARGREAVES, THORNTHWAITE, MISSING DATA
 
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