Guidelines for Validating Bowen Ratio Data

Abstract

ABSTRACT. For a variety of reasons, the measurement of latent heat flux using the Bowen ratio method can sometimes result in erroneous data. This study provides guidelines for detecting erroneous Bowen ratio data and illustrates the application of these guidelines by comparingvapotranspiration (ET) from a surface can either be measured or estimated. Because measuring ET is difficult and requires specialized equipment, most applications use ET estimates instead of direct measurements. ET can be estimated from meteorological, crop, and soil information using a variety of methods, as reviewed by Doorenbos and Pruitt (1977), Jensen et al. (1990), andAllen et al. (1998). However, for some applications, especially in research, direct measurement of ET is necessary.For decades, precision weighing lysimeters have been the standard for the direct measurement of ET. If lysimeters are not available, the Bowen ratio method is often used as an alternative to lysimetric measurements (Moran et al., 1989;Kustas et al., 1999;Devitt et al., 1998;Dugas et al., 1998;Prueger et al., 1997;Cellier and Olioso, 1993).Although the theory for this method has been known for a long time (Bowen, 1926), its practical application has only been possible in recent decades, as adequate instrumentation has been developed. This method is based on the theory that one-dimensional fluxes of sensible and latent heat can be described in terms of flux-gradient relationships (Tanner, 1988): Substituting equations 1 and 2 into equation 3, and assuming K h = K w (Verma et al., 1978;Cellier and Brunet, 1992), b can be obtained from (Bowen, 1926):where g = (C p P/el) is the psychrometric constant (kPa °C -1 ), and DT and De are obtained by measuring air temperature and vapor pressure or dew point at two heights above the top of the canopy, within the boundary layer. The one-dimensional surface energy balance equation is as follows:where R n = net radiation (W m -2 ) G = soil heat flux (W m -2 ). E

Surface energy exchange and evapotranspiration from cotton crop under full irrigation conditions in the Rio Grande do Norte State, Brazilian Semi-Arid

“…To avoid errors in the estimation of the BREB fluxes, data when -1.25 < β < -0.75, when values for which the measurements of gradients of temperatures and vapor pressure were lower than the resolution limit of the sensors, and when the wind speed at the upper height was lower than 1.0 m s -1 and the difference of the wind speed between both heights was lower than 0.3 m s -1 of the sensors were eliminated (Payero et al, 2003). Each eliminated value was replaced by interpolation between two values that preceded and followed the eliminated value.…”

Reply to referee #2

“…The second flag is for the case where the Bowen ratio approaches −1, which causes the uncertainty in the BREB fluxes to be very high, as the denominator of Eqs. (12) and (13) approaches 0 (Payero et al, 2003):…”

“…Schematic overview of the measurement setup at the tower. 500 m radius it is possible to find native tree species such as beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylvestris L.), as well as the introduced species hemlock (Tsuga heterophylla (Rafinesque) Sargent) and Japanese larch (Larix kaempferi (Lambert) Carriére) (Erisman et al, 1998;Raj et al, 2014;Su et al, 2009;Bosveld and Bouten, 2001;Tietema et al, 2002;Van Wijk et al, 2000;Weligepolage et al, 2013). Canopy heights differ between cover types depending on species and growing stage.…”

“…The study site has an oceanic climate (Cfb) under the Köpen classification system, with a yearly average temperature of 9.8 • C and an average precipitation of 910 mm yr −1 (Sluijter, 2011). The topography is slightly undulating with smooth height differences (Raj et al, 2014), a well-drained soil, and a groundwater table below 40 m depth (Tiktak and Bouten, 1994). The soil texture ranges from fine sand to sandy loam (Weligepolage et al, 2012;Tietema et al, 2002;Van Wijk et al, 2000).…”

Lysimeter-Based Water Use and Crop Coefficient of Drip-Irrigated Potato in an Arid Environment

“…Micrometeorological approaches, like the Eddy covariance and Bowen ratio techniques, have been widely used in recent times for indirectly measuring ET [3][4][5][6][7]. On the other hand, lysimeters are still the standard method for directly measuring ET [8].…”