Estimation of standardized reference evapotranspiration on the Canadian Prairies using simple models with limited weather data

Abstract

Potential evapotranspiration (PET) can be accurately determined with a Penman-Monteith model, however this model requires many different inputs which are not measured at most climatic stations. The agricultural region of the Canadian Prairies is a large geographic region of similar dry continental climate (cold semi-arid to subhumid) and could benefit from simple, yet accurate models for determination of evapotranspiration. The purpose of our study was to develop simple (limited data) ET models to estimate ET that was calculated using the ASCE standardized reference Penman-Monteith equation. We used daily weather data from 2003 and 2004 from ten stations across the agricultural region of the prairies. We compared our developed models to other published simple models by Baier-Robertson, Hargreaves, and Linacre. All models used the standardized reference evapotranspiration as the comparison standard. Using individual climatic stations within and outside the data set used to develop our models, we compared averages, standard errors, regression parameters r, slope, and intercept, as well as the coefficient of efficiency accuracy of fit. Of the temperature based models (which included calculated extraterrestrial radiation), our model and Hargreave’s model were the most accurate. Temperature-humidity models improved the estimate of evapotranspiration, compared to temperature based models. The Linacre and the Baier-Robertson temperature and temperature-humidity models were not accurate and are not recommended for estimating evapotranspiration in the Canadian Prairies. Incorporation of temperature, humidity and wind speed into a physically based model resulted in the most accurate and precise estimation of standardized reference evapotranspiration.