Strategy for applying scaling technique to water retention curves of forest soils
Abstract
Describing the infiltration of water in soils on a forested hillslope requires the information of spatial variability of water retention curve (WRC). By using a scaling technique, Hayashi et al. (2009), found that the porosity mostly characterizes the spatial variability of the WRCs on a forested hillslope. This scaling technique was based on a model, which assumes a lognormal pore size distribution and contains three parameters: the median of log-transformed pore radius, ψm, the variance of log-transformed pore radius, σ, and the effective porosity, θe. Thus, in the scaling method proposed by Hayashi et al. (2009), θe is a scaling factor, which should be determined for each individual soil, and that ψm and σ are reference parameter common for the whole data set. They examined this scaling method using θe calculated as a difference between the observed saturated water content and water content observed at ψ = -1000 cm for each sample and, ψm and σ derived from the whole data set of WRCs on the slope. Then it was showed that this scaling method could explain almost 90 % of the spatial variability in WRCs on the forested hillslope. However, this method requires the whole data set of WRCs for deriving the reference parameters (ψm and σ). For applying the scaling technique more practically, in this study, we tested a scaling method using the reference parameter derived from the WRCs at a small part of the slope. In order to examine the proposed scaling method, the WRCs for the 246 undisturbed forest soil samples, collected at 15 points distributed from downslope to upslope segments, were observed. In the proposed scaling method, we optimized the common ψm and σ to the WRCs for six soil samples, collected at one point on the middle-slope, and applied these parameters to a reference parameter for the whole data sets. The scaling method proposed by this study exhibited an increase of only 6 % in the residual sum of squares as compared with that of the method using the whole data set of WRCs. This result showed that on the natural forested hillslope, the scaling method proposed by Hayashi et al. (2009) can describe the spatial variability in WRCs well without the whole data sets of WRCs on the slope. Reference Hayashi, Y., K. Kosugi, and T. Mizuyama. 2009. Characterization of soil WRCs of a natural forested hillslope using a scaling technique based on a lognormal pore-size distribution.Soil Science Society of America Journal. 73:55-64
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H41F0962H
- Keywords:
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- 1838 HYDROLOGY / Infiltration;
- 1849 HYDROLOGY / Numerical approximations and analysis;
- 1865 HYDROLOGY / Soils;
- 1875 HYDROLOGY / Vadose zone