A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Effects of Deforestation in Amazoniaon the Local Hydrological Cycle:The Scale-Dependence IssueCassiano D’Almeida 1 , Charles J. Vörösmarty 1 , Fekete Balazs 1 ,José A. Marengo 2 , Lelys B. de Guenni 3 , Cort J. Willmott 41 CSRC/UNH/USA2 CPTEC/INPE/BRAZIL3 Simon Bolivar University/VENEZUELA4 University of Delaware/USACassiano D’AlmeidaCSRC/University of New HampshireMorse Hall, Durham, NH 03824 USAcassiano@eos.sr.unh.eduDespite all the concern from the scientific community on major impacts ofAmazonian deforestation, its effects on the regional hydrological cycle are still uncertain.While many modeling studies have observed that large-scale conversion of theAmazonian rainforest into pastures, or croplands tend to induce an overall reduction inprecipitation, there are also meso-scale experiments that predicted the establishment ofenhanced rainfall over deforested areas. These contrasting results suggest that the neteffect of deforestation on precipitation might depend on the size of the clearing area.However, precipitation in Amazonia follows more closely the fluctuations in thegeneral circulation of the atmosphere, which seems to be still offsetting the effects ofdeforestation. Since runoff is not directly dependent on such remote forcings, it may,unlike precipitation, carry the signal of deforestation and permit a better assessment onthe scale-dependence of its effects.The present work applies different methods of Trend Analysis to historicaldischarge records in the Amazon Basin, to detect significant trends potentially associatedwith deforestation. Spectral Analysis is also applied to identify significant oscillationspresent in the data, which are then removed after the application of suitable frequencyfilters. Based on current and predicted deforestation scenarios, a numerical modelrepresenting the Water Budget Closure (WBC) system in Amazonia is also applied,providing high-resolution gridded runoff and discharge outputs.Preliminary results indicate the existence of organized spatial patterns in thetrends of non-filtered discharge records, indicating a potential association with deforestedareas. After removing significant oscillations from these records – determined frompower spectrum calculations –, these patterns might get intensified. The application ofWBC as proposed, will assess the coherence of deforestation and trend patterns.