15 © 2020 Conscientia Beam. All Rights Reserved. ESTIMATING REFERENCE EVAPOTRANSPIRATION BY HARGREAVES AND BLANEY-CRIDDLE METHODS IN HUMID SUBTROPICAL CONDITIONS Muhammad Hafeez 1+ Zia Ahmad Chatha 2 Alamgir Akhtar Khan 3 Allah Bakhsh 4 Abdul Basit 5 Fatima Tahira 6 1 Department of Agricultural Engineering, Faculty of Agricultural Sciences and Technology, Bahauddin Zakariya University, Multan, Pakistan. 2 Department of Food Engineering, Faculty of Agricultural Engineering, UAF, Faisalabad, Pakistan. 3 Department of Agricultural Engineering, MNSUA, Multan, Pakistan. 4,5 Department of Botany, Ghazi University, Dera Ghazi Khan, Pakistan. 6 Department of Mathematics, Institute of Southern Punjab, Multan, Pakistan. (+ Corresponding author) ABSTRACT Article History Received: 21 January 2020 Revised: 25 February 2020 Accepted: 30 March 2020 Published: 27 April 2020 Keywords Blaney-Criddle Hargreaves Humid subtropical ETo Islamabad Kakul Pakistan. Various methods are available to predict reference evapotranspiration (ETo) but the Penman-Monteith (PM) ETo method has been considered to be the most accurate ETo method to determine ETo. The PM ETo method can be solved by various weather parameters like atmospheric temperature, wind velocity, moisture content and net solar radiations. There are many weather stations in the world that have no complete set of weather parameters to predict ETo by applying PM ETo method. So alternative ETo methods like Hargreaves (HG) and Blaney-Criddle (BC) ETo methods are used which need only a fewer number of weather parameters. In this paper, two ETo methods, HG and BC are compared with PM ETo method in humid subtropical climatic conditions of Islamabad and Kakul (Abbottabad) weather stations. The study indicate that HG ETo method overestimated PM ETo method by 23.78% at Islamabad weather station and 28.47% at Kakul station. The BC ETo method overestimated PM ETo method by 37.93% at Islamabad weather station and by 22.68% at Kakul weather station. The dissimilarity of HG ETo method with PM ETo method with RMSE was 1.09 mm/day at Islamabad weather station and 1.17 mm/day at Kakul weather station. The dissimilarity of BC ETo method with PM ETo method has Root Mean Square Error (RMSE) of 2.86 mm/day at Islamabad weather station and 1.48 mm/day at Kakul weather station. Contribution/Originality: The objective of this investigation is to compare ETo by HG and BC ETo methods with PM ETo method in humid subtropical climatic conditions of Pakistan. 1. INTRODUCTION The usage of high calorie and meat-intensive food consumption are estimated to approximately twice by 2050 due to increasing of population to fulfill the diet security in the next decades, significant variations in agricultural water management are needed [1]. From January to April in 2010, a severe sacristy occur in southwest China, which thread more than sixty million public and produced greater than 23.66 billion financial fatalities [2]. In distinction to the increasing requirement on irrigated yield, water for agriculture has been decreased due to regular Current Research in Agricultural Sciences 2020 Vol. 7, No. 1, pp. 15-22. ISSN(e): 2312-6418 ISSN(p): 2313-3716 DOI: 10.18488/journal.68.2020.71.15.22 © 2020 Conscientia Beam. All Rights Reserved.