Independent estimation of sensible and latent fluxes in a vineyard using improved surface renewal analysis

Abstract

Turbulent fluxes are key components of surface energy balance. Micrometeorological techniques, such as eddy covariance (EC), are commonly used to estimate sensible (H) and latent (LE) heat fluxes, because they provide direct measurements and do not interfere with the normal crop canopy development. However, EC has technical difficulties, strict size, and surface homogeneity requirements and is relatively expensive. Surface renewal analysis (SRA) is a promising alternative for turbulent flux estimation, because it is more economical, has less-stringent fetch requirements, and can be deployed in heterogeneous canopies or markedly sloped surfaces. Castellví (SRA_Cast) presented a methodology to estimate H using SRA, avoiding the high-frequency wind speed records that are necessary for determining stability and friction velocity, which are then used to calibrate the α parameter (a factor that corrects the nonuniform heating of an air parcel). Instead, an iterative procedure using wind speed recorded using a simple cup anemometer can be used. Here, we estimated sensible and latent heat fluxes and latent heat flux as residual from the energy–balance equation using SRA_Cast during January 2018 and compared the results with EC measurements in a trilled vineyard (heterogeneous canopy), in Pirque, Santiago de Chile. Values of H and LE through SRA_Cast present a high agreement with EC, with slopes (b) of 1.11 and 0.88 and coefficients of determination (R²) of 0.97 and 0.89, respectively. LE_{res_SRA} showed values of 1.60 and 0.80 for b and R², respectively. Energy balance closure was slightly better for SRA than for EC (b, 0.73 and 0.71; R², 0.94 and 0.95), proving to be a reasonably good and simpler alternative for turbulent flux estimation.