Collaborative Research: The Role of Canopy Structure on Variability of Water and Heat Fluxes from Forested Watersheds

Duke University, Durham NC

Investigators

Abstract

9902957 Albertson This study investigates the exchange of water vapor, energy, and momentum between forested watersheds and the atmospheric boundary layer (ABL), using a combination of emerging tools in numerical simulation of turbulent flow and transport through and above plant canopies and recent result from a comprehensive field campaign. The field experiment, conducted in October of 1997, included seven research groups measuring land surface fluxes of water vapor, heat, carbon dioxide, and momentum on seven towers situated within a pine forest at Duke Forest near Durham, North Carolina. The data set studied here is the first comprehensive experiment that includes simultaneous velocity statistics and flux measurements at as many as seven locations in the canopy sublayer of a forest along with detailed leaf area density profile measurements in space. To explore and generalize the relationship between forest structure and observed heat and water vapor fluxes, an investigation using three-dimensional Large Eddy Simulations (LES) is proposed. These simulations are the first to explicitly consider variability in leaf area density in space and employ radiative transfer schemes to realistically account for energy attenuation by foliage elements. The simulations, which treat the foliage as a multiply-connected porous medium, will permit investigating how the spatial structure of forest canopies interact with energy/radiation and the turbulent transport dynamics to give rise to the observed spatial patterns in land surface flux fields within and above the canopy. An anticipated result is an understanding of what spatial variability in fluxes could be attributed to spatial variability in canopy structure for flux measurements within the canopy sublayer. The results from this study will guide future field experiments that seek to estimate forest-wide average fluxes from tower measurement and will rigorously assess the range of applicability of one-dimensional canopy models.