Relationship of area-averaged carbon dioxide and water vapour fluxes to atmospheric variables

Area-averaged fluxes are constructed from a combination of aircraft and tower data collected during BOREAS. The averaging area includes both conifer and deciduous forests, wetlands, burned areas and bodies of water. The area-averaged water vapour flux is closely related to the area-averaged solar radiation while the area-averaged carbon dioxide flux and water use efficiency (WUE) are more related to the vapour pressure deficit (VPD). In spite of the fact that the averaging encompasses a variety of ecosystems, various relationships for the area-averaged water vapour and carbon dioxide fluxes show comparable or less scatter than those based on fluxes from individual sites. Possible causes of this unexpected result are discussed but no conclusions are offered.