A test for a see-saw oscillation between the Amazon and Congo basins using regional climate modeling

Abstract

The Amazon and Congo basins represent two of the three largest regions of rainfall found on the globe. Eltahir et al. (2004) have proposed the existence of a "see-saw" oscillation between these two basins, where a reduction of rainfall in one region is marked by an increase in the other. This inverse relationship has been observed both directly by Eltahir et al., using satellite data of regional rainfall (Simpson et al. 1988), and indirectly through changes in river flow measurements (Amarasekera et al. 1977) during the last century. However, little work has been done to study this see-saw effect through the use of climate models. Using a regional climate model (RegCM), the appearance of the oscillation was tested by converting rainforest area in one basin into two different land types, simulating drought-like climate conditions to induce additional rainfall in the other basin. In total, one control run and four land-modified runs were simulated for this experiment. The effects of these conditions were modeled over a one-year period (1980). It was found that in some cases, reduction of rainfall in one basin resulted in increased rainfall in small areas of the other; however, over the entirety of both basins, evidence of the see-saw hypothesis was not simulated. Several factors may have contributed to this result, including the limitations associated with using a regional model, as well as the initial conditions set for the five climate simulations.