2004 Volume 17 Issue 3 Pages 264-273
By analyzing the time series of measurements of soil moisture at a point along with precipitation and potential evaporation using the bucket with a bottom hole (BBH) model, we evaluated water balance terms at the point. The estimates of those terms made at nine points on a 1.5m grid in a small grass-covered area showed their own spatial variations. The results obtained are summarized as follows.
(a) Ranking of the spatial variability of the water balance terms involved in the BBH model was W (soil moisture) < E (evaporation) < Rs (surface runoff) < Gd (gravity drainage).
(b) Clear patterns showing the spatial variation in surface runoff and gravity drainage in a 3×3m patch were obtained, which suggests that subsurface water below the ASSL (30cm thick) has flow systems on spatial scales of a few meters.
(c) The spatial variation patterns of the water balance terms obtained by the parameterization of the BBH model did not necessarily agree with that of soil moisture but showed ones peculiar to the terms. This means that the parameterization takes the effects of other factors than soil moisture such as the micro topographic relief, vegetation cover, soil texture and structure into account appropriately, because such factors should by nature exhibit spatially not random but organized variations.
(d) Daily evaporation estimates made by the BBH model were in good agreement with the measurements taken for reference by the Bowen ratio method, though it was conducted by the expedient of disregarding an insufficiency of fetch and neglecting the heat flux into the soil.
