Determining evapotranspiration and crop coefficient values using an adjusted Penman-Monteith equation over canola (Brassica napus) in southern Manitoba
Date
2019-06-13
Authors
Britton, Tony
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The FAO-56 Penman-Monteith equation and crop coefficients were adjusted to better represent modern canola (Brassica napus) grown in Manitoba at three locations. It was hypothesized that incorporating direct measurements of available energy, developing crop coefficients using leaf area index values, or incorporating a water stress coefficient could improve the equation’s accuracy in comparison to direct eddy covariance evapotranspiration measurements. Measured average daily evapotranspiration ranged from 3.35 ± 1.70 (S.D.) mm day-1 (Miami) to 3.38 ± 1.78 mm day-1 (Glenlea). Most model adjustment combinations allowed cumulative evapotranspiration to be within 10% of measured cumulative evapotranspiration while the original FAO-56 equation estimated above the upper 10% error threshold at all locations. Growing season root mean square error and mean relative error values were lowest when all model improvements excluding the water stress coefficient were included. Improvements allow greater confidence in the FAO-56 Penman-Monteith equation’s representation of canola evapotranspiration in Manitoba.
Description
Keywords
Evapotranspiration, Eddy covariance, Penman-Monteith, Agrometeorology, Crop coefficient