Wednesday, 30 May 2012
Rooftop Ballroom (Omni Parker House)
The vegetal cover has been changed by natural and human activities. These changes have altered regional and global climates through biophysical and biogeochemical processes. In this work, the effects of land cover change (LCC) on the energy and carbon balance in the semiarid region of Brazil are analyzed using the Integrated Biosphere Simulator (IBIS) model. In each simulation conducted, it was considered a different type of vegetation cover on a grid point (9° 03 ' 30.6 '' S; 40° 19 ' 45.1 '' W). The caatinga is the predominant natural vegetation observed in the study area; thus, the first simulation assumes that the grid is completely covered by caatinga (dense shrubland); the second simulation was completely covered by pasture, and the third simulation was covered by degraded caatinga. Results of a simulated conversion from complete caatinga cover to pasture and to degraded caatinga explain that surface albedo (at wet and dry season) increases, consequently the energy balance was altered. Maximum rates of daytime Net Ecosystem CO2 Exchange (NEE) during the wet season (JanuaryMarch) period were, on average, 2.8 µmol m2 s1 for caatinga while for degraded caatinga were, on average, 0.6 µmol m2 s1 (negative values denote net ecosystem CO2 uptake). It indicates that the metabolic activity of the ecosystem decreased and this land cover (degraded caatinga) is acting as a source of CO2 to the atmosphere, however with low rates. Moreover, the Net Primary Production (NPP) also decreases with the land cover conversion. It is emphasized that this was the first step of the experiment. The second step of this experiment is being done to assess the Impact of LCC on surface energy and carbon balance using the IBIS-2.6 model coupled to Center for Weather Forecasting and Climate Studies AGCM (MCGA/CPTEC/IBIS-2.6, Kubota and Bonatti, 2009). We are using the model version with 28 levels and T126 horizontal resolution. Two numerical runs are performed. In the control run, NEB is covered by its natural vegetation (caatinga); in the land cover change run, NEB vegetation is changed to pasture. Each run consists of five 6-yr numerical integrations. The present work has important implications for land use management issues in semiarid region of Brazil, including efforts to restore and preserve the natural ecosystem. This study also provides more evidence for the need to consider anthropogenic land cover change when evaluating climate trends.
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