Quantification Of Leaf Emissivities Of Forest Species: Effects On Modelled Energy And Matter Fluxes In Forest Ecosystems

Abstract

Climate  change  has distinct regional and local differences in its impacts on the land sur face. One of the important parameters determining the climate change signal is the emissivity (ε) of the sur face. In forest-climate interactions, the leaf sur face emissivity plays a decisive   role.  The accurate  determination  of leaf emissivities  is crucial for  the appropriate  interpretation  of measured  energy and matter fluxes between the forest and the atmosphere. In this study, we quantified the emissivity of the five broadleaf tree species Acer pseudoplatanus, Fagus sylvatica, Fraxinus excelsior, Populus simonii and Populus candicans. Measurements of leaf sur face temperatures were conducted under laboratory conditions in a controlled-climate chamber within the temperature range of +8 °C and +32°C. Based on these measurements, broadband  leaf emissivities ε (ε for the spectral range of 8-14 µm) were calculated. Average ε_{8-14 µm} was 0.958±0.002 for all species with very little variation among species. In a second step, the soil-vegetation-atmosphere  transfer model ‘MixFor-SVAT ’ was applied to examine the effects of ε changes on radiative, sensible and latent energy  fluxes of the Hainich  forest in Central Germany.  Model experiments  were driven by meteorological data measured at the Hainich  site. The simulations  were  forced with the calculated ε value as well as with minimum and maximum values obtained from the literature.  Significant  effects  of ε changes were detected.  The strongest  effect was identified for the sensible heat flux with a sensitivity of 20.7 % per 1 % ε change. Thus, the variability of ε should be considered in climate change studies.