Evaluation of Two Surface Renewal Methods for Calculating the Sensible Heat Flux over a Tea Field Ecosystem in Hilly Terrain

Abstract

Seasonal drought happens frequently in the lower slope hilly areas of China, which leads to a huge economic loss to China’s famous tea production. An accurate determination of the evapotranspiration (ET) value of different seasons can provide a crucial decision parameter for irrigation management. The surface renewal (SR) method is an accurate and inexpensive method compared with the eddy covariance (EC) method, which is widely used to calculate the sensible heat flux (H). The latent heat flux (LE) evapotranspiration can be estimated indirectly when combined with the energy–balance equation. This research investigated the traditional and improved calculation methods of H (SRsnyder and SRchen), based on the surface renewal theory, over a tea field for one year. The calculation accuracy was obtained from the statistical analysis between the SR and EC methods. Different months’ applicability was evaluated to determine the best calculation method for the tea field. The traditional calculation method (SRsnyder) is based on the van slope model using the second, third, and fifth structure function. The improved SR model (SRchen) introduces a third order temperature function and friction velocity for calculation. The results indicate that SRchen shows a good calculation accuracy of H in the spring seasons (February to April), summer (May to July), and autumn (August to October). The determination coefficients of regression analysis (R2) ranges were [0.66, 0.88] with most values greater than 0.8. The root mean square error (RMSE) ranges were [34.15, 69.22] W/m2. However, during this period, SRsnyder had a poor calculation accuracy of H, and the range of R2 was [0.45, 0.74] with the RMSE ranges of [32.28, 63.25] W/m2. In the winter (November to January), the calculation accuracy of both models was relatively low with R2 almost 30% lower than that of other seasons. Therefore, this study suggests the use of the SRchen method to estimate the H of a tea field ecosystem in the low slope hilly area of the Yangtze River region in the spring, summer, and autumn. While in the winter, the SRsnyder method is recommended.