Comparative Analysis of Reference Evapotranspiration by Hargreaves and Blaney-Criddle Equations in Semi-Arid Climatic Conditions

Abstract

There are various equations for calculation of reference evapotranspiration (ETo), but the Penman-Monteith (PM FAO-56) equation has been considered as the standard ETo equation. The key problem of PM FAO-56 equation is that it uses large number of weather parameters like air temperature, wind velocity, humidity and sun radiation as input. These weather parameters are not accessible at all weather stations of the world especially in developing countries. So, ablatives ETo equations like Hargreaves (HG) and Blaney-Criddle (BC) equations are used for estimation of ETo which required very small number of weather parameters that are readily available at most of the weather stations of the world. A research is conducted to compare HG and BC ETo equations for estimation of monthly ETo under semi-arid climatic regions of Lahore, Faisalabad and Peshawar, Pakistan. The PM FAO-56 ETo equation is considered as reference ETo equation for the assessment of HG ETo and BC ETo equation. The statistical results indicate that HG ETo equation overestimates PM FAO-56 ETo method by 7.91% at Lahore weather station, 5.59 % at Faisalabad weather station and 11.95% at Peshawar weather station. The BC ETo equation overestimates PM FAO-56 ETo equation by 34.345% at Lahore weather station, 28.637% at Faisalabad weather station and 21.44% at Peshawar weather station. The variation of HG ETo equation with PM FAO-56 ETo equation with RMSE of 0.487 mm/day at Lahore weather station, 0.521 mm/day at Faisalabad weather station and 0.985 at Peshawar weather station is noted. The variation of BC ETo equation with PM FAO-56 ETo equation having RMSE of 3.03 at Lahore weather station, 2.58 at Faisalabad weather station and 1.96 at Peshawar weather station is noted. Contribution/Originality: The objectives of this study is to compare the HG ETo and BC) ETo equations against FAO-56 PM ETo equation in semi-arid climatic conditions. 1. INTRODUCTION Pakistan is under the problem of water shortage and the demand of water for irrigation is also increased due to mounting demand of food and fiber [1]. Pakistan is in between the arid to semi-arid region [2]. The knowledge of

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“…They concluded that the Hargreaves-Samani equation calibrated with the maximum temperature is better than those calibrated with other meteorological data. Similarly, monthly ET values were computed using the modified Blaney-Criddle and Hargreaves-Samani equations, obtaining data from three stations located in the semi-arid climate regions of Pakistan and compared with PM-driven ET values [38]. Overall, it was stated in the study that both equations overestimated PMdriven ET values, although the findings of the Hargreaves-Samani method were superior to those of the modified Blaney-Criddle method.…”

“…However, it is important to note that a zero correlation does not necessarily imply the absence of any relationship between the variables; it simply means that there is no linear relationship [67]. DET quantifies the model's goodness of fit and can be expressed as shown in Equation (38). It is a statistical metric that determines the proportion of the variance in the dependent variable that is explained by the independent variables in a regression model.…”

Estimation of Reference Evapotranspiration in a Semi-Arid Region of Mexico

“…The accuracy of the HS and BC equations has been evaluated by several authors, comparing their results with the FAO-56 Penman–Monteith (PM) reference method; HS was the equation that attained the best fit in semi-arid regions [ 32 , 33 ]. Other authors state that the HS method works well in most climatic regions, except for wet areas where it tends to overestimate ET 0 [ 16 , 34 , 35 , 36 ].…”