Collaborative Research: Precipitation and Streamflow Reconstruction and Analysis in the Amazon River Basin

Tree ring reconstruction of paleoclimate in the tropics is challenging because tropical trees rarely have reliable annual banding. Consequently, the climate history of tropical areas like the Amazon of South America is poorly known, including how recent flood and drought extremes are typical of natural climate fluctuations, or if they are attributable to global climate warming and deforestation. Cedrela odorata has been demonstrated to grow annual rings that can be used to reconstruct wet-season precipitation in the eastern Amazon. This project will use C. odorata and historical records to create a 250 to 300 year long record of rainfall extremes in the eastern Amazon, constrain the elevations of high and low river levels in the 19th century, and use climate and water cycle models to determine what are the physical mechanisms that govern the occurrence of floods and droughts in the region, including the impact of deforestation. The project will also investigate the paleoclimate potential of another species, Denezia excelsa, develop an outreach and education website on the forests and climate of the Amazon, and lead workshops on tree ring dating methods. The amplitude of difference between the seasonal high and low flows of the Amazon appear to be increasing, however in the absence of a long-term record of high- and low-stands through time, it is not clear whether these recent observations are within the range of natural fluctuations, or if anthropogenic climate change or deforestation play roles. This project will use new tree-ring records of hydroclimate and historical records from the Brazilian Digital library to reconstruct Amazon River extremes through time. The physical mechanisms behind drought and flood extremes in the Amazon, including Pacific and Atlantic sea surface temperature forcing and the potential role of a fully forested vs partially deforested watershed will be explored with the Community Earth System Model Version 2.1 (CESM2.1). Climate model output will be input into a hydrologic model of the Amazon River system for the spatial reconstruction of 19th century high and low flow extremes identified with tree-ring and historical information and to test the impact of forest cover loss on river levels in the Amazon. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.