Effects of interannual variation and interdecadal trend on the Amazon Basin climate and global circulation

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St. Croix, Kathryn Julia
Major Professor
Chen, Tsing-Chang
Takle, Eugene S.
Committee Member
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The purpose of this study is to look at the factors impacting the climate of the Amazon Basin and the global circulation patterns. Currently mass deforestation is affecting the climate, species and overall existence of the tropical forests of the Amazon Basin. Sources show that Amazonian deforestation rates are as high as 20,000 to 50,000 km2 per year (Nobre et al, 1991; and Shukla et al, 1990). Many deforestation studies (Dickinson and Henderson-Sellers et al, 1988; Nobre et al, 1991; etc.) used models to simulate Amazon deforestation to assess the impacts deforestation has on the regional climate. Overall deforestation studies found a decrease in regional rainfall, evapotranspiration, and moisture flux convergence and an increase in surface temperature due to imposed deforestation. However, the deforestation studies did not look at the possibility that other climate factors also influence the Amazon Basin. Overall, this study's results show that the interannual variation and interdecadal trends in Amazon Basin rainfall and heating affect the regional climate and the global circulation patterns. An interannual variation exists over the Amazon Basin creating a variation Southern Hemisphere summers with a larger than average or smaller than average rainfall and moisture flux convergence totals, defined as wet or dry summers. An interdecadal increase in Amazon Basin rainfall, precipitable water and moisture flux convergence are also found over the region by the use of long-term station data and NCEP/NCAR reanalysis data. The interannual variation and interdecadal increase in Amazon Basin rainfall alter the divergent and rotational circulation patterns as well. The changes in the rotational circulation patterns during wet and dry seasons and the interdecadal patterns are also generated by a simplified barotropic model with an imposed forcing over the Amazon Basin that simulates the interannual variation in regional rainfall and heating. An in depth comparison between the interannual variation and interdecadal results and the deforestation studies found that; (1) the interannual wet season changes and the interdecadal changes suppress the regional drying and decrease in Amazon rainfall and, (2) moisture flux convergence due to deforestation and interannual dry season changes enhance the drying and decrease in Amazon Basin moisture due to deforestation.