Effects of deforestation & climate change on carbon & water cycling in Amazonia

Andes-Amazon Project
Tom Powell, Naomi Levine, Ke Zhang
The purpose of the Andes-Amazon Project is to predict how land-cover along with changes in climate will affect the composition, structure, and functioning of the Amazonian ecosystem over the next century. Using a combination of terrestrial models and field measurements, researchers will discover the role of land-cover change and climate in driving savannization of the Amazon and determine forest sensitivity to associated changes in climate, carbon flux, and hydrology.

Is deforestation changing the hydrologic climate and vegetation dynamics of the Amazon?
Marcos Longo
The Amazon forest has experienced significant deforestation since the 1970s. Approximately 17% of the original forest has been converted to pasture for cattle grazing or croplands. In the past, deforestation has occurred near the availability of paved road access. Currently, the Brazilian government plans to increase the number of paved roads in the Amazon, which may increase the deforestation of yet undisturbed areas. The impact of deforestation on rainfall in the Amazon is still unclear, but a massive deforestation is likely to reduce evapotranspiration, affecting the overall water cycle strength. This can lead to a decrease in precipitation and an increase in drought frequency. Deforestation, however, is not yet widespread, and the current deforestation scale may induce atmospheric circulations that can potentially reorganize patterns of precipitation rather than merely reducing it. In both cases, the remaining forest experiences a significant change in water and light availability, which could alter the state of the ecosystem. To understand these biosphere-atmosphere interactions resulting from deforestation, we use a state-of–the-art fully-coupled biosphere-atmosphere model (ED2-BRAMS). By considering the complex interactions between the biome and the atmospheric circulations, and by utilizing land use change scenarios that realistically represent regions likely to be deforested, we aim to better understand dynamic changes in precipitation and vegetation in the Amazon.

What impact will projected changes in climate and atmospheric [CO2] have on the Amazon forest?
Tom Powell
Climate models predict that a reduction in precipitation over much of the Amazon basin will be one of the consequences of climate change. Both field studies and models have shown considerable dieback of the Amazon forest when exposed to a prolonged and extreme reduction in precipitation. We are using data from our recent field campaigns to the Caxiuanã National Forest and Tapajó's National Forest in Brazil to parameterize a mechanistic representation of water movement through the soil-plant-atmosphere continuum in the ED model.  This hydrodynamic formulation in ED will be parameterized to represent drought tolerant and intolerant plant functional types, which will enable us to explore the mechanisms by which tropical trees succumb to drought and how their resilience is modulated by rising atmospheric CO2. This research is supported in part by the NSF-Amazon PIRE project, which seeks to build international partnerships between emerging scientists in the U.S. and Brazil.  This research is also supported by an NSF Doctoral Dissertation Improvement Grant.

Tree Canopy

The Fate of Amazonian Ecosystems and Eco-hydrological Consequences Under Projected Climate and Land-use Changes
Ke Zhang
Deforestation and drought have imposed regional-scale perturbations onto Amazonian ecosystems and are predicted to cause large negative impacts on the Amazonian ecosystems and associated regional carbon dynamics in the 21st century. However, global climate models (GCMs) vary greatly in their projections of future climate change in Amazonia, giving rise to uncertainty in the expected fate of the Amazonian ecosystems over the coming century. In this study, we explore the possible eco-hydrological consequences of the Amazonian ecosystems under projected climate and land-use changes in the 21st century using a suite of state-of-the-art biosphere models driven by three representative, bias-corrected climate projections from three IPCC GCMs, coupled with two land-use change scenarios (a business-as-usual and a strict governance scenario). We identify the relative roles of climate change, CO2 fertilization, land-use change and fire, and their synergies in driving the projected composition and structure of the Amazonian ecosystems. 

Canopy in Amazonia