HR: 11:30h
AN: H22A-05    [Abstracts]
TI: Remote Sensing of Semiarid Ecosystems: Methods for Determining How Water Availability Affects Vegetation Pattern and Process
AU: * Scanlon, T M
EM: tms2v@virginia.edu
AF: University of Virginia, Department of Environmental Sciences Clark Hall, Charlottesville, VA 22903 United States
AB: A combination of field investigations, modeling, and satellite remote sensing over spatial scales ranging from O10⁰-10⁵ m are used to infer how water availability governs the distribution and function of semi-arid vegetation. The Kalahari Transect (KT) in southern Africa, which spans a north-south aridity gradient from approximately 1600 mm to 200 mm of mean annual rainfall, was selected as the field setting for this investigation due to its features that are amenable for remote sensing, which include uniform sandy soils and level topography. At the landscape scale, high-resolution IKONOS images reveal that tree clustering at sites along the KT is fractal, and cellular automata modeling indicates that this spatial organization is driven by interannual variability in rainfall. The IKONOS images also allow us to assess how landscape heterogeneity affects land-atmosphere interaction in terms of the spatial variability of evapotranspiration. A large eddy simulation model applied to the remotely-sensed boundary conditions shows that water availability profoundly affects the degree of spatial coupling between the vegetation and surface fluxes. At the regional scale, 16-year time series of NDVI fields from the AVHRR sensor combined with ground-based rainfall fields enable quantification of the land cover distribution (tree, grass, bare soil) over the entire transect. The vegetation functional types respond to water availability at vastly different timescales: a soil moisture model applied to the satellite-derived land cover reveals that tree density is highly correlated with long-term mean rainfall, while the annual extent of grass cover can be successfully simulated by considering only the transient availability of near-surface soil moisture and the tree cover at a particular location. These results suggest that mixed tree/grass semi-arid ecosystems are ideally suited to reach a dynamic equilibrium with respect to the use of a fluctuating limiting resource (water) by having functional components that responds to variability in rainfall over long timescales (trees) and short timescales (grasses).
DE: 0400 Biogeosciences
DE: 1818 Evapotranspiration
DE: 1854 Precipitation (3354)
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2005 Joint Assembly