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Hargreaves versus Penman-Monteith under Humid Conditions

2007; American Society of Civil Engineers; Volume: 133; Issue: 1 Linguagem: Inglês

10.1061/(asce)0733-9437(2007)133

1943-4774

Slaviša Trajković,

Solar Radiation and Photovoltaics

The Food and Agriculture Organization of the United Nations (FAO) has proposed using the Penman-Monteith equation as the standard for estimating reference evapotranspiration (ET0), and for evaluating other equations. The basic obstacle to using the FAO-56 Penman-Monteith equation (FAO-56 PM) widely is the required weather data which are not available in most of the stations. In such circumstances, a simple empirical Hargreaves equation (HARG) is often used. However, this equation generally overestimates ET0 at humid locations. Therefore, HARG requires local calibration. The main objective of this study is to investigate the possibility for calibrating the equation in the Western Balkans region, South East Europe through the adjustment of Hargreaves exponent (HE). Data from Palic, Sarajevo, and Nis have been used for estimating the adjusted HE. A value of 0.424 is proposed instead of the original 0.5 as one which should be used in the adjusted Hargreaves equation (AHARG) for the Western Balkan locations. The ET0 values estimated by AHARG were compared with FAO-56 PM estimates for eight humid locations (Varazdin, Zagreb, Bihac, Novi Sad, Negotin, Kragujevac, Nis, and Vranje). Estimates by AHARG were in close agreement with FAO-56 PM estimates at most of the locations. The SEE ranged from 0.17mmday−1 for Varazdin to 0.24mmday−1 for Vranje, averaging 0.21mmday−1. The average overestimation was about 1%. These results strongly support the use of the adjusted Hargreaves equation at humid Western Balkan locations in the case when only the temperature data are available. Further research should be undertaken for evaluating the validity of the approach presented in this paper in other regions.