Effects of evolving canopy structure on turbulence statistics in and above a hedgerow vineyard

Abstract:

Vertical profiles of mean flow and turbulence statistics have been already studied over several vegetation types, leading to a thorough characterization of turbulent field properties within and above the canopy space in spite of high complexity of the processes. However, only few studies investigated the influence of slow canopy seasonal structural changes on turbulent flow, and the few available datasets are usually limited to measurements before and after foliage growth. Seasonal variations of foliage density play a crucial role increasing canopy roughness and, consequently, determining the degree of coupling between vegetation and the atmosphere. Therefore, the study of turbulent transport processes along with a regular monitoring of foliage growth are required both to parameterize higher order closure models and to improve the prediction of bulk aerodynamic properties during the canopy developing period.

The aim of this study was to follow the continuous evolution of turbulent statistics from budbreak to fully developed foliage in a hedgerow vineyard in the North East of Italy. Synchronous measurements from a vertical profile of five sonic anemometers on a 5 m tower have been collected at 20 Hz from beginning of April to mid of July 2015. In the same period, detailed measurements of Leaf Area Density (LAD) profile and canopy architecture were performed at regular intervals (ca. weekly) around the tower. Mean flow, scaled turbulence statistics (σ_w/u*, σ_u/u*) profiles and turbulent kinetic energy budget correlate with canopy development and determine the degree of coupling between lower atmosphere and the canopy space. Peculiar geometrical structure of the hedgerow vineyard also imposes a strong directional behaviour of mean flow inside the canopy.

The knowledge of the evolution of turbulent flow around growing canopies is necessary to fully understand and model mass and energy exchanges of natural and managed vegetation.