Representativeness of Eddy-Covariance flux footprints for areas surrounding AmeriFlux sites

Large datasets of greenhouse gas and energy surface-atmosphere fluxes measured with the eddy-covariance technique (e.g., FLUXNET2015, AmeriFlux BASE) are widely used to benchmark models remote-sensing products. This study addresses one major challenges facing model-data integration: To what spatial extent do flux measurements taken at individual sites reflect model- or satellite-based grid cells? We evaluate footprints—the temporally dynamic source areas that contribute fluxes—and representativeness these footprints for target within 250–3000 m radii around towers) often in flux-data synthesis modeling studies. examine land-cover composition vegetation characteristics, represented here by Enhanced Vegetation Index (EVI), across 214 sites, potential biases as a consequence footprint-to-target-area mismatch. Monthly 80% footprint climatologies vary through time ranging four orders magnitude from 103 107 m2 due measurement heights, underlying vegetation- ground-surface wind directions, turbulent state atmosphere. Few located truly homogeneous landscape. Thus, common integration approaches use fixed-extent area introduce on order 4%–20% EVI 6%–20% dominant land cover percentage. These site-specific functions extents, land-surface characteristics. advocate need be awareness, especially research applications against data products explicit information. propose simple index based our evaluations can guide identify site-periods suitable specific provide general guidance use.