Upscaling of saturated conductivity for Hortonian runoff modelling

Stochastic and deterministic upscaling techniques are developed that upscale saturated conductivity at the support of 0.04 m(2) to representative actual infiltration (I-b) for support units (blocks) of 10(1)-10(4) m(2), as a function of steady state rainfall and runon to the block, under Hortonian runoff (infiltration excess overland flow). Parameters in the upscaling techniques represent the surface runoff flow pattern and the spatial probability distribution of saturated conductivity within the 10(1)-10(4) m(2) block. The stochastic upscaling technique represents the spatial process of infiltration and runoff using a simple process-imitating model, estimating I-b using Monte Carlo simulation. The deterministic upscaling technique aggregates these processes by a deterministic function relating rainfall and runon to I-b. The stochastic upscaling technique is shown to be capable to upscale saturated conductivity derived from ring infiltrometers to I-b values of plots (1 m(2)) corresponding to measured I-b values using rainfall simulators. It is shown that both upscaling techniques can be used to estimate I-b for each time step and each block in transient rainfall-runoff models, giving better estimates of cumulative runoff from a hillslope and a small catchment than model runs that do not use upscaling techniques. (c) 2005 Elsevier Ltd. All rights reserved.