A Statistical Comparison of Reference Evapotranspiration Methods: A Case Study from Jharkhand State of India

ABSTRACT: Agricultural planning relying on evapotranspiration suffers due to inaccuracy in its estimation. The nonavailability of meteorological parameters required for accurate estimation of reference evapotranspiration (ET o ) resulted in the development of different methods of ET o estimation. The present study compares various universally accepted methods of ET o estimation by considering the Penman Monteith as a standard method. Comparative analysis indicated the suitability of Hargreaves (1985) method followed by Christiansen (1968) method and Pan Evaporation method (1977) . The improvement in ET o estimation was carried out through transformation of standard equations using single or multi parametric approach after analyzing dependency and sensitivity of different meteorological parameters on ET o . The developed transformed models indicated that during ET o estimation morning time relative humidity (RH 1 ) can play the dominant role (99%). ET o estimation by combination of bright sunshine hours and wind speed (WV) exhibit better role (98.8%) than the combination of minimum temperature (Tmin) and WV (98.6%). Keywords: Evapotranspiration, statistics, transformed model, meteorological parameters I. INTRODUCTION Evapotranspiration constitutes the most significant component of the hydrologic budget apart from precipitation. It is simply the amount of water returned to the atmosphere through evaporation and transpiration. It is an important climatic factor, but its accurate estimation is very difficult. Evapotranspiration varies regionally and seasonally according to weather and wind conditions. Due to this variability, water managers who are responsible for planning the distribution of water resources need to have a thorough understanding of the evapotranspiration process and knowledge about the spatial and temporal rates of evapotranspiration. The evapotranspiration rate is a function of factors such as temperature, solar radiation, humidity, wind and characteristics of the specific vegetation that is transpiring, which may vary significantly between vegetation type