| Regional-scale catchments are characterised
typically by natural variability in climatic and land-surface features. This
paper addresses the important question regarding the appropriate level of
spatial disaggregation necessary to guarantee a hydrologically sound
consideration of this variability. Using a simple hydrologic model along with
physical catchment data, the problem is reconsidered as a model parameter
identification problem. With this manner of thinking the subjective nature as to
what to include in the disaggregation scheme is removed and the problem
reconsidered in terms of what can be supported by the available data. With such
an approach the relative merit of different catchment disaggregation schemes is
viewed in terms of their ability to provide constrained parameterisations that
can be explained in terms of the physical processes deemed active within a
catchment. The outlined methodology was tested for a regional-scale catchment,
located in eastern Australia, and involved using the quasi-distributed VIC
catchment model to recover the characteristic responses resulting from the
disaggregation of the catchment into combinations of climate, soil and
vegetation characteristics. A land-surface classification based on a combination
of soil depth and land cover type was found to provide the most accurate
streamflow predictions during a 10-year validation period. Investigation of the
uncertainty associated with the predictions due to weakly identified parameters
however, revealed that a simpler classification based solely on land cover
actually provided a more robust parameterisation of streamflow response. The
result alludes to the hydrological importance of distinguishing between forested
and non-forested land cover types at the regional-scale, and suggests that given
additional information soil-depth / storage considerations may also have proved
significant. Improvements to the outlined method are discussed in terms of
increasing the informative content available to differentiate between competing
catchment responses.
Keywords: regional-scale, spatial variability,
disaggregation, hydrotype, quasi-distributed, parameterisation, uncertainty |