HR: 0830h
AN: B41C-0911    [PDF]
TI: The impact of the degree of forest fragmentation on dry-season Amazonian precipitation
AU: Weaver, C P
EM: weaver@cep.rutgers.edu
AF: Rutgers University, Center for Environmental Prediction 14 College Farm Road, New Brunswick, NJ 08901 United States
AU: * Baidya Roy, S
EM: sroy@princeton.edu
AF: Princeton University, Department of Ecology and Evolutionary Biology, Princeton, NJ 08540 United States
AU: Pacala, S W
EM: pacala@princeton.edu
AF: Princeton University, Department of Ecology and Evolutionary Biology, Princeton, NJ 08540 United States
AB: Numerical experiments have suggested that wholesale destruction of tropical forests on continental scales can lead to a large-scale decrease in precipitation. Other work, focusing on smaller scales (e.g., similar to those of local watersheds), has shown that mesoscale landscape heterogeneity, e.g., due to partial deforestation, can induce atmospheric circulations that can alter the intensity and spatial distribution of the pre-existing pattern of precipitation. One consequence of this might be a local enhancement of precipitation in a given region, which in turn could strongly impact watershed-scale hydrological and ecological processes. Therefore, the net impact on total rainfall for a given amount and pattern of deforestation (i.e., the degree of fragmentation) remains an open question. We have carried out a suite of high-resolution, month-long simulations with the Regional Atmospheric Modeling System (RAMS) to investigate the sensitivity to different imposed forest fragmentation patterns, based on satellite-observations of human-caused deforestation. These fragmentation patterns range from highly fragmented to highly clumped (though all with the same mean amount of deforestation). From these experiments we find that the degree of forest fragmentation significantly affects the monthly total rainfall in the simulation domain. This variability in total rainfall can be linked to the intensity and organization of landscape-forced mesoscale circulations and the associated vertical motion and atmospheric stability field. The key point is that forest areas interspersed with many small-scale patches of grassland or pasture can experience different total rainfall, on monthly timescales, than forest areas with fewer, larger deforested patches, even given the same total deforested area. This implies that ecological processes that are both (i) sensitive to rainfall and (ii) help control vegetation patchiness may lead to significant hydrologic feedbacks. Such feedbacks could have important consequences for the subsequent evolution of forest systems under a combination of human and natural pressures.
DE: 0315 Biosphere/atmosphere interactions
DE: 3307 Boundary layer processes
DE: 3337 Numerical modeling and data assimilation
SC: Biogeosciences [B]
MN: 2003 Fall Meeting