16-Comparison of Newly Proposed Copais Approach and Traditional Reference Evapotranspiration Equations in a Small Catchment.

Abstract

Reference crop evapotranspiration (ET0) is a key influential factor in many agricultural and hydrological projects. Alexandris and Kerkides (2003) and Alexandris et al. (2006) proposed a new empirical formula for hourly and daily estimations of reference evapotranspiration which requires data for three pertinent meteorological attributes, solar radiation Rs, air temperature T, and relative humidity RH. In this study, four reference evapotranspiration (ET) equations were compared using the weather data for five years (1995-1999) from a weather station at the Brue catchment, the United Kingdom. The PenmanMonteith equation standardized by the Food and Agriculture Organization (FA056-PM) was used to compare with the California Irrigation Management Information System (CIMIS) Penman equation, the Penman—Monteith equation standardized by the American Society of Civil Engineers, and the new empirical equation (Copais Approach) with limited meteorological data. Yearly, monthly, daily and hourly comparisons of ET() were made using statistical terms like Linear Regression Correlation Coefficient (R2) values, Root Mean Squared Differences (RMSE) and Standard Error of Estimates (SEE). The study showed that ET0 values estimated by the other evaporation methods correlated very well with the corresponding values estimated by the standardized Penman—Monteith equations in both hourly and daily time steps. This study also demonstrated that the newly proposed empirical equation (Copais approach) for hourly reference evapotranspiration worked quite efficiently with a reasonably good accuracy.