Albedo of an Amazon tropical rainforest: field measurements, remote sensing, modeling, and its influence on the regional climate / Albedo de uma floresta tropical Amazônica: medições de campo, sensoriamento remoto, modelagem, e sua influência no clima regional

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Albedo is defined as a ratio between reflected solar radiation and incoming solar radiation over a surface. It is a main factor that affects the terrestrial radiation balance and has been frequently considered in the global and regional climate studies. Amazon is one of planets regions where the response of regional atmospheric circulation is more intense. Simulation studies using several models show that a conversion of tropical rainforest in pasturelands causes reduction in the local precipitation, which is mainly dependent of surface albedo changes. The objective of present work is to investigate the sources of spatial and temporal variation of an Amazon tropical rainforest surface albedo, using field measurements, modeling and satellite products; and to investigate the role of surface albedo changes, after Amazon tropical deforestation, in the regional climate. In this work it was used observed data from four forests (Caxiuanã, Cuieiras, Ducke and Jaru Reserves) and two pastures (Dimona and Nossa Senhora Aparecida) belonging to LBA (Large-Scale Biosphere-Atmosphere Experiment in Amazonia) and ABRACOS (Anglo Brazilian Amazonian Climate Observation Study) projects. It was also used six different satellite systems: CG99, ERBE, SRB/ISLSCP2, UMD and MODIS white-sky and MODIS blacksky. For the simulation of Amazon tropical rainforest surface albedo the point IBIS (Integrated Biosphere Simulator) model and it coupled to CCM3 climate model was used. The results of this work show that: the main sources of variation of albedo in hourly and monthly scale are the vegetation cover and atmospheric transmissivity, and that the canopy wetness is an important source of variation in hourly scale and should be included in the models; that the simulated albedo show strong sensitivity to superior canopy parameters of leaf orientation and infrared reflectance and no sensitivity was found for the lower canopy parameters, consistent with the canopy structure; that an incorporation of canopy wetness in the radiative transfer calculation improve the results in a hourly scale, reducing the albedo during the hours with precipitation, but not in a seasonal scale, excluding the canopy wetness as a main source of the seasonal variability in tropical rainforest; that the different satellite systems present a considerable variation related to the field measured albedos, including great seasonal differences; that the precipitation anomalies can be explained by a linear relationship between radiative processes, where the changes in surface albedo and net radiation explain approximately 96% and 99% of the annual variation of precipitation and that the replacement of forest by soybean cropland affects more the regional climate than the conversion in pasture, probably due to the high value of soybean cropland albedo

ASSUNTO(S)

sensoriamento remoto climatologia albedo modelagem modeling albedo remote sensing

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