Thursday, 17 January 2002: 9:00 AM
Interaction of natural and anthropogenic factors in Amazon rainfall
Changes to the hydrologic cycle of the Amazon Basin produced by deforestation have been investigated in several climate modeling studies. Such changes must however be viewed in the context of natural fluctions of Amazon precipitation, which on an interannual basis are primarily related to ENSO. Here we evalute interactions of deforestation with interannual variability using ensembles of CCM3 simulations for the AMIP-II period (1979-1996). Ensemble results are compared for simulations which use (i) observed SSTs with undisturbed landscape; (ii) climatological SSTs with undisturbed landscape; (iii) observed SSTs with Amazonian deforestation; and (iv) climatological SSTs with Amazonian deforestation. The use of ensembles of relatively long-term (17 year) simulations for each case yields more robust results than previous studies, which mostly used shorter-term simulations.
Results indicate that deforestation and interannual fluctuations attributable to sea-surface temperature variations interact in a fundamentally nonlinear manner. Response to deforestation depends significantly on the phase of the ENSO cycle, so that the background natural variability of Amazon circulation and precipitation must be accounted for in evaluating the effects of deforestation.