HR: 14:40h
AN: H23G-05 INVITED     [Abstracts]
TI: Watershed characterization by spectral analysis of hydrological and hydrochemical time series
AU: * Kirchner, J W
EM: kirchner@seismo.berkeley.edu
AF: University of California, Department of Earth and Planetary Science, 307 McCone Hall, Berkeley, CA 94720-4767 United States
AB: Physically-based models attempt to link catchment behavior with measurable physical and chemical properties of the landscape. However, the properties of interest are usually heterogeneous on all scales, and are typically only directly measurable at scales many orders of magnitude smaller than the catchment itself. While it seems obvious that catchment models should be 'physically based,' it seems less obvious how those models should be based on physics. Although the physics underlying hydrology has been understood for decades, it is often unclear how to apply those physical laws to systems that are complex, heterogeneous at all scales, and poorly characterized by direct measurement. Thus most 'physically based' models rely on an implicit up-scaling premise, which assumes that the same governing equations that hold at the point scale will also hold at the catchment scale, with 'effective' values of the parameters determined by calibration. We need to consider the possibility that this up-scaling premise may be wrong, and that the effective governing equations for such heterogeneous systems at large scale may be different in form, not just different in the parameters, from the equations that describe the small-scale physics. Determining these large-scale governing equations will require insightful analyses of catchment-scale behavior. Here I use spectral analysis to characterize two important timescales of catchment hydrological response: the travel time distribution (i.e., how long it takes raindrops to emerge from the catchment as streamflow), and the hydraulic response function (i.e., how long it takes stream water fluxes to respond to rainfall inputs). I show that the characteristic timescale of hydraulic response is much shorter than the characteristic travel time of water through the catchment. I also show that these two quantities obey fundamentally different distributions, with different scaling properties. These patterns of behavior would not necessarily be obvious from consideration of the small-scale physics of subsurface transport. Thus these observations provide important constraints for theories of catchment hydrology.
DE: 1839 Hydrologic scaling
DE: 1847 Modeling
DE: 1860 Streamflow
DE: 1872 Time series analysis (3270, 4277, 4475)
DE: 1879 Watershed
SC: Hydrology [H]
MN: Fall Meeting 2005