Estimation and Application of Bowen Ratio Fluxes over Crop Surfaces - An Overview

Abstract

Bowen-ratio (~) is defined as the ratio of sensible heat flux (H} to the latent heat flux (LE) from a surface and its values varies from 0.1 over tropical oceans to greater than 10 over deserts. The Bowen ratio - energy balance (BREB) metllOd is the simple yet most practical method for estimating latent and sensible heat i1uxes from any surface. It is estimated from the principle of conservation of energy and combines measurement oftemperature and vapour pressure gradients apmt from net radiation (QJl) and soil heat flux to give estimate of energy and mass fluxes over a surface. If advection is negligible and P is small and positive, this method measures the surface fluxes accurately. ThiS method is useful in estimating evapotranspiration (ET) oyer canopy in various stages of crop growth as well as LE/QI1' which is a better indicator of crop water demand than either crop coefficient or crop factor. In semi-arid environment, BT esti!llation over the crop surface with non-exchanging psychrometer is comparable to the Iysimetric measurements.