Submitted to: Southwest Hydrology
Publication Type: Review Article
Publication Acceptance Date: 11/16/2007
Publication Date: 1/1/2008
Citation: Baker, J.M. 2008. Challenges and Cautions in Measuring Evapotranspiration. Southwest Hydrology. 7(1):24-25.
Technical Abstract: Our ability to measure evapotranspiration has improved dramatically in recent years, and several methods have been adapted into commercially-available systems. However, potential practitioners should understand the conditions under which these systems can be used and the limits on their accuracy. The two principal methods are Bowen ratio/energy balance (BREB) and eddy covariance. The BREB approach is robust, but it is an indirect method that requires the measurement of net radiation, soil heat flux, and gradients of both temperature and humidity. All of these measurements have errors associated with them, limiting the overall accuracy of the ET measurement. Eddy covariance is a more direct measurement, but there are several corrections that must be applied, so data analysis is more complicated. Both methods require uniform sites of large size to satisfy the need for adequate upwind fetch. Either approach can yield reasonable accuracy, but the user must be knowledgeable, and the instruments must be maintained and periodically calibrated.