Scale – dependent effects on the surface energy fluxes modelling in heterogeneous/complex ecosystems using the Two-Source Energy Balance (TSEB)

Abstract:

A key assumption of two source energy balance models is that the effective source/sink for turbulent flux exchange at the surface and the entire canopy/soil is described by a bulk surface/canopy/soil temperature and resistance. Therefore, the spatial resolution of radiometric surface/canopy/soil temperature (T_RAD) used as an input to these models and how well they agreed with this “bulk” concept influence the final estimations. In complex ecosystems, with more than two layers of vegetation, bare soil and heterogeneous distribution patterns, the representativeness of the sensor average temperature and the up-scaling of the ecosystem structural vegetation characteristics will be more crucial for the precision of the results than in more homogeneous landscapes. The aim of this study is to analyze the scale-effects derived from TSEB application, comparing the observed energy fluxes and the estimated ones obtained from multiple T_RAD data sources of different nature (tree/grass/soil ground-based observations, tower footprint and low and medium satellite T_RAD) and how the up-scaling of the vegetation characteristics contribute to the discrepancies. The area selected for this purpose is a savanna type FLUXNET site (Tonzi ranch, CA, US). These ecosystems present canopy mosaics that differ in phenology, physiology and functioning, and bare soil, all of them influencing the turbulent and radiative exchanges.