Simplifying daily evapotranspiration estimates over short full-canopy crops

A knowledge of daily evapotranspiration (lambdaE) from surface radiative te mperature at a regional scale is of interest in agronomy, The aerodynamic f ormulation and the radiative Bowen ratio-energy balance method provide good estimates of instantaneous lambdaE based on remote-sensed canopy temperatu res, Instantaneous latent heat nux estimates for the daytime period ran be integrated to obtain a value for daily lambdaE when detailed crop knowledge and continuous meteorological measurements are available. We propose a dif ferent method for estimating daily evapotranspiration for short, unstressed crops with a leaf area index (LAI) > 3. The method is based on the radiati ve Bowen ratio-energy balance method and on the similarity between the diur nal course of lambdaE and solar irradiance. This regression-based approach uses continuous measurements of air vapor pressure, air temperature, surfac e radiative temperature, and solar irradiance during daylight hours. Moreov er, detailed crop knowledge is not required. The method was tested in a Med iterranean area with semicontinental climatic characteristics on grass (Fes tuca arundinacea Schreb.), wheat (Triticum aestivum L.), and alfalfa (Medic ago sativa L.). Daily lambdaE was estimated with an error <15% compared wit h estimates of <lambda>E made using a Bowen ratio-energy balance equipment. This new approach is promising for remote sensing applications at a region al scale, although it requires further verification for other climatologica l conditions.