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

摘要

Climate change has distinct regional and local differences in its impacts onthe land surface. One of the important parameters determining the climate change signalis the emissivity (ε) of the surface. In forest-climate interactions, the leaf surface emissivityplays a decisive role. The accurate determination of leaf emissivities is crucial for theappropriate interpretation of measured energy and matter fluxes between the forestand the atmosphere. In this study, we quantified the emissivity of the five broadleaf treespecies Acer pseudoplatanus, Fagus sylvatica, Fraxinus excelsior, Populus simonii and Populuscandicans. Measurements of leaf surface temperatures were conducted under laboratoryconditions 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 rangeof 8-14 μm) were calculated. Average ε8-14 μm was 0.958±0.002 for all species with very littlevariation 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 andlatent energy fluxes of the Hainich forest in Central Germany. Model experiments weredriven by meteorological data measured at the Hainich site. The simulations were forcedwith the calculated ε value as well as with minimum and maximum values obtained fromthe literature. Significant effects of ε changes were detected. The strongest effect wasidentified for the sensible heat flux with a sensitivity of 20.7 % per 1 % ε change. Thus, thevariability of ε should be considered in climate change studies.