HR: 08:00h
AN: H21F-01 INVITED     [Abstracts]
TI: On the nature and causes of hydrological variability and scale effects
AU: * Sivapalan, M
EM: sivapala@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Departments of Geography and Civil and Environmental Engineering, 220 Davenport Hall, 607 S. Mathews Avenue, Urbana, IL 61801 United States
AB: Land surface hydrology involves the study of the interactions between the atmosphere and the land surface, occurring over multiple space-time scales, crucial for many hydrological applications. Hydrological effects of these interactions can be divided, as a first approximation, into two groups: 1) those associated with the wetting phase, focusing on rainfall to runoff relationships, and 2) those associated with the drying phase, focusing on evapotranspiration. Of course, some processes, such as subsurface drainage, operate continuously during both phases. During the wetting phase, the space-time variabilities resulting from the interactions undergo, firstly, a concentrating action in the spatial domain (due to topography, soil layering and the river network), and a smoothing or filtering action in the time domain (due to the flow over and within the hillslopes). Observed streamflow hydrograph at a catchment's outlet embeds within it all of the spatial and temporal variability associated with runoff processes occurring within the entire catchment area. This space-to-time transformation is a reflection of the distribution of travel distances to the outlet, combined with the distributions of travel velocities along a multiplicity of pathways. During the drying phase, there is a continuation of the movement of soil moisture vertically towards the groundwater table and down-slope towards the stream network, contributing to the recession curve and more generally to low flows. However, an additional force takes over through the drying action of the atmosphere. Because of the nonlinearity in the drying process, i.e. the rate of drying decreases as drying proceeds, the drying action of the atmosphere works against the concentrating action of the topography, to return the surface soil moisture back to one controlled by soil properties. In the temporal domain, however, the evapotranspiration process varies at time scales ranging from a few milliseconds to many decades. At small time scales, of the order of seconds to an hour, it is governed by atmospheric turbulence, at intermediate scales (of the order of hours to days) it is governed by the hourly (diurnal) and daily variations of radiation, mean wind, humidity and land surface soil moisture, while over much longer time scales (of the order of months to years), it is governed by the seasonality of soil moisture, plant physiology and phenology. This paper will present examples of these variabilities in catchments from around the world, and their ramifications for flood estimation, water balance modeling and water quality predictions.
DE: 1813 Eco-hydrology
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1839 Hydrologic scaling
DE: 1860 Streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005