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

Abstract

Climate\xa0 change\xa0 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 ( e ) of the sur face. In forest-climate interactions, the leaf sur face emissivity plays a decisive\xa0\xa0 role.\xa0 The accurate\xa0 determination\xa0 of leaf emissivities\xa0 is crucial for\xa0 the appropriate\xa0 interpretation\xa0 of measured\xa0 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\xa0 leaf emissivities e ( e for the spectral range of 8-14 µm) were calculated. Average e 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\xa0 transfer model ‘MixFor-SVAT ’ was applied to examine the effects of e changes on radiative, sensible and latent energy\xa0 fluxes of the Hainich\xa0 forest in Central Germany.\xa0 Model experiments\xa0 were driven by meteorological data measured at the Hainich\xa0 site. The simulations\xa0 were\xa0 forced with the calculated e value as well as with minimum and maximum values obtained from the literature.\xa0 Significant\xa0 effects\xa0 of e changes were detected.\xa0 The strongest\xa0 effect was identified for the sensible heat flux with a sensitivity of 20.7 % per 1 % e change. Thus, the variability of e should be considered in climate change studies.