HR: 08:15h
AN: B31E-02 INVITED    [Abstracts]
TI: Ecohydrologic Hypotheses Revisited: Global Synthesis with Canopy-Scale, FLUXNET Observations
AU: * Williams, C A
EM: caw@umbc.edu
AF: University of Maryland Baltimore County, GEST, Biospheric Sciences, Code 614.4 NASA GSFC, Greenbelt, MD 20771, United States
AU: Reichstein, M
EM: mreichstein@bgc-jena.mpg.de
AF: Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Str. 10, Jena, 07745, Germany
AU: Buchmann, N
EM: nina.buchmann@ipw.agrl.ethz.ch
AF: Institute of Plant Science, Grasslands, ETH Zurich, LFW C 56 Universitätstrasse 2, Zurich, 8092, Switzerland
AU: Baldocchi, D
EM: biomet@nature.berkeley.edu
AF: Department of Environmental Science, Policy & Management, University of California Berkeley, 345 Hilgard Hall, Berkeley, CA 94720, United States
AU: Papale, D
EM: darpap@unitus.it
AF: Laboratoria di Ecologia Forestale, Di. S.A.F.Ri.- Facolta di Agraria, Via Camillo de Lellis, Viterbo, 01100, Italy
AU: Beer, C
EM: cbeer@bgc-jena.mpg.de
AF: Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Str. 10, Jena, 07745, Germany
AB: Global synthesis of canopy-scale evapotranspiration measurements shows smooth transition from water-limited to energy-limited control, broadly consistent with catchment-scale relations and of a surprisingly similar functional form to that proposed by Budyko. Annual evaporative index (evaporated fraction of annual precipitation) tends to be reduced by precipitation in the form of snow as well as seasonal hydrologic surplus. Unexpectedly, grasslands tend to have a higher ratio of actual to potential evapotranspiration than treed landscapes, particularly savannas and shrublands. Control of daily evapotranspiration by soil moisture and potential evapotranspiration is well described by a logistic function akin to the two-stage model of evaporation decay, except during spring thaw when soil moisture can be high but ecosystems evapotranspire relatively little. Sites with seasonal droughts following periods of hydrologic surplus demonstrate significant water storage capacity that sustains evapotranspiration during periods of water deficit. Taken together, a simple framework of supply- or demand- limited evapotranspiration is supported by global FLUXNET observations, however climate seasonality and variability, the timescale of analysis, as well as vegetation cover all exert additional control.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1833 Hydroclimatology
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2007 Fall Meeting