Foley, Jon: California Academy of Sciences (Project Lead)
Project Funding:
2007 - 2010
NRA: 2006 NASA: Interdisciplinary Research in Earth Science
Funded by NASA
Abstract:
This proposal aims to improve our understanding of how the expansion and intensification of agriculture - including shifting cropping and deforestation practices, plus changing levels of agricultural inputs from fertilizers and irrigation - have affected terrestrial ecosystems across the world and their biogeochemical and biophysical coupling to the climate system. The study has four major objectives: Objective #1 - Documenting Shifting Patterns of Global Agriculture. In order to examine the environmental consequences of agricultural land use, it is important to not only understand the patterns of agricultural land cover (e.g., cropland, pasture), but also of land-use practices (e.g., crop selection, fertilizer use, irrigation, tillage). Using a combination of satellite-based measurements and detailed agricultural census databases, we will derive new spatially explicit, global datasets of agricultural land cover (for croplands, pastures) and land use practices (crop selection and yield, fertilizer inputs, irrigation and tillage). Objective #2 - Documenting Shifting Deforestation Practices in the Tropics. Until recently, characterizing deforestation has largely focused on estimating the changing areas of "forest" and "non-forest" pixels over time. However, tropical landscapes are highly dynamic and complex: they experience cycles of clearing, cultivation, grazing and secondary forest re-growth, resulting in a complex mosaic of intact rainforest, agricultural lands under varying management regimes, and recovering secondary forests. Using a new "hybrid" technique - blending coarse-resolution remote sensing products, fine-resolution satellite data and detailed ground-based surveys - we will examine and document the pan-tropical patterns of gross forest clearing, agricultural land use, and subsequent abandonment and forest re-growth. Furthermore, we will determine characteristic land-cover transition rates following deforestation across the tropics, so that these data may be used in next-generation carbon cycle and coupled carbon-climate models. Objective #3 - Examining Impacts of Changing Agricultural Practices on Terrestrial Ecosystems. We will use a highly integrated, off-line terrestrial ecosystem model (PEGASUS), in conjunction with datasets derived in Objectives #1 and #2, to explore how global ecological and hydrological systems are responding to changes in agricultural land use and management practices (i.e. changing crop selections, increasing fertilizer use and irrigation, shifting fallow cycles, differing modes of deforestation and abandonment). We will use this off-line model, which is far more computationally efficient than our coupled CCSM-IBIS climate-biosphere model, for key hypothesis testing, parameter estimation, algorithm testing, and model validation studies. We will specifically consider global-scale changes in productivity, carbon storage, soil nutrient balance, and continental-scale river discharge. Objective #4 - Exploring Impacts of Agriculture on Coupled Climate-Biosphere System. Finally, we will use a next-generation coupled climate-biosphere model (CCSM-IBIS), with new, detailed treatments of global agricultural lands (including detailed treatments of sub-grid processes, multiple crop types, management systems, fertilizer inputs, and irrigation) to examine the coupling between terrestrial ecosystems and the atmosphere. Using this model, we will consider how agricultural land use practices affect both the biophysical (through energy / water balance) and biogeochemical (through CO2) linkages between terrestrial ecosystems and the atmosphere, paying particular attention to the tropics. We will also work to redefine the notion of "radiative forcing" and "global climatic sensitivity" of the climate system, which overlooks the impacts of land-cover change.
More details may be found in the following project profile(s):