Effects of soil heat storage and phase shift correction on energy balance closure of paddy fields

Abstract

RESUMENSe utilizó el método de covarianza eddy para medir los flujos de energía en un arrozal con ahorro de agua de riego en la Llanura del Sur de China, durante la etapa de crecimiento del arroz en 2013. También se analiza la respuesta del balance de energía superficial al cambio de almacenamiento térmico en el suelo entre las placas de flujo térmico enterradas a una profundidad específica y la superficie, y la corrección del desfase de los componentes del balance de energía, por medio de tres métodos estadísticos: mínimos cuadrados ordinarios (MCO), proporción del balance de energía (PBE) y remanente del balance de energía (D). Los resultados muestran que la curva de los MCO se incrementó 8.8% en promedio y el PBE medio diario aumentó 0.5% después de considerar el cambio en el almacenamiento térmico del suelo. El rango de las magnitudes de D registradas cada media hora varía de -129-260 W m -2 a -102-194 W m -2 , y los valores absolutos de D decrecieron 9.9% en promedio. Tomando en cuenta la fase de corrección, el incremento en los coeficientes de regresión de los MCO (con un promedio de 11.3%) y el decremento de D en las mediciones realizadas cada media hora (que van de -61 a 176 W m -2 ), ambos indicaron que la corrección de la fase de desplazamiento mejoró el cierre del balance de energía superficial en escalas de media hora, especialmente entre el amanecer y el mediodía, pero careció de utilidad en la escala diaria. Esto indica que ambos métodos son útiles para mejorar el grado del cierre del balance de energía, representado en diferentes escalas temporales con un índice de evaluación adecuado. Es necesario realizar investigaciones ulteriores que presten mayor atención a otros aspectos de la corrección. ABSTRACTThe eddy covariance technique was used to measure the energy fluxes of a paddy field under water-saving irrigation in the South China Plain for the stage of rice growth in 2013. This study analyzed the energy balance components and evaluated the energy balance closure. The study also discussed the response of surface energy balance to the change in soil heat storage between the heat flux plates buried at a specific depth and the surface, and the phase shift correction of energy balance components, by using three different statistical methods, namely ordinary least squares (OLS), energy balance ratio (EBR), and energy balance residual (D). The results showed that the OLS slope increased by an average of 8.8%, and the mean daily EBR increased by 5.0% after considering the change in soil heat storage. The range of half-hourly D over a four-month period decreased from -129 -260 W m −2 to -102 -194 W m −2, and the absolute value of D decreased by 9.9% on the average. Considering the phase correction, the increase in OLS regression coefficients with an average of 11.3% and the decrease in half-hourly D, ranging from -61 to 176 W m −2 , both indicated that phase shift correction improved the surface energy balance closure at the half-hourly scale, specifically in the period from sunrise to noon, but had no...

Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

“…As reported by different studies, the omission of the soil heat storage results in the underestimation of the energy EBC by up to 7 %. For instance, Liu et al (2017) reported an increase in OLS slope of an average 8.8 % and a mean daily EBR increase of 5 % when the soil heat storage term was considered in their study in the Taihu Lake region of the Southern China Plain. In their study in the three sites in the Badan Jaran desert, Li et al (2014) analysed the effect of including soil heat storage derived by different methods in the energy balance closure; their EBR improved by between 1.5 and 4 %.…”

Surface Energy Partitioning and Evaporative Fraction in a Water-Saving Irrigated Rice Field

“…Energy balance closure was evaluated via the energy balance ratio (EBR) method, which was calculated based on the cumulative available energy (Rn -G) and turbulent energy fluxes (LE + Hs) over specific time periods. Both hourly and daily EBR were improved by including the fluxes correction [11] compared with the results for original measurements (Figure 1), with an average increase of 14.5% and 12.8% for the hourly and daily scale, respectively. Yet, the energy fluxes measured by the EC system are not completely closed after the correction due to the energy balance deficit problem, although the mean daily EBR (0.93 and 0.85 in 2015 and 2016 rice seasons, respectively) of the EC measurement in the WSI rice fields was acceptable.…”

“…The value of EF fluctuates greatly before sunset among observation days, as seen from the error bar in Figure 2. This was ascribed to the large temperature variation, unstable atmospheric turbulence, and advection exchange at sunset, and the inaccurate instantaneous fluxes measurement by the EC system [11]. In addition, the EF was occasionally greater than 1 during the transition periods in the morning or evening (at 7:00-8:00 and 15:00-16:00).…”

“…The surface energy budget has been measured in many different terrestrial ecosystems using the eddy covariance (EC) technique. However, the energy fluxes measured by the EC system are not completely closed due to the systematic and random errors, as indicated in the literature [6][7][8][9][10][11].…”

Determining Threshold Values for a Crop Water Stress Index-Based Center Pivot Irrigation with Optimum Grain Yield

“…The inclusion of border plots effectively separated irrigation treatments. To induce slight drought and promote the penetration of roots of wheat, the irrigation quota was reduced at the over-winter and jointing stages, whereas more water was delivered at the critical flowering and filling stages [40,41]. The amount of full irrigation (I4) was calculated according to Equation (1), and detailed information of irrigation for different treatments was presented in Table 1.…”