Upscaling in Computational Hydrology: Chasing after the “Holy Grail”

Title of talk: Upscaling in Computational Hydrology: Chasing after the “Holy Grail”

Scale issues are ever-present in the modelling of hydrologic processes. While hydrologists have a fairly refined understanding of the drivers of changing soil moisture, snow melt, and evaporative demand at the scale of a single soil plot, snow pillow, or plant, determining how these ‘point-scale processes’ integrate over a hillside, farm, or watershed is elusive. Explicitly modelling all of the detail is nigh impossible. This is due the naturally occurring heterogeneity in any environment, the difficulty of practically characterizing heterogeneous internal properties and states, and our inability to measure integrated fluxes anywhere but at stream gauges. Computational hydrologists have developed a number of approaches for addressing this combined lack of system knowledge at scales of interest via ‘upscaling’ approaches which attempt to represent the net behavior of a system driven by point-scale physics over a heterogeneous domain, in effect replacing the complications of a heterogeneous world with new physical relations which describe the dependence of bulk fluxes upon bulk storage and (often) statistical descriptions of internal heterogeneity.