Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 4.256 IF 4.256
  • IF 5-year value: 4.819 IF 5-year
    4.819
  • CiteScore value: 4.10 CiteScore
    4.10
  • SNIP value: 1.412 SNIP 1.412
  • SJR value: 2.023 SJR 2.023
  • IPP value: 3.97 IPP 3.97
  • h5-index value: 58 h5-index 58
  • Scimago H <br class='hide-on-tablet hide-on-mobile'>index value: 99 Scimago H
    index 99
Volume 13, issue 12 | Copyright
Hydrol. Earth Syst. Sci., 13, 2399-2412, 2009
https://doi.org/10.5194/hess-13-2399-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  14 Dec 2009

14 Dec 2009

Reducing scale dependence in TOPMODEL using a dimensionless topographic index

A. Ducharne A. Ducharne
  • Laboratoire Sisyphe, CNRS/UPMC, Paris, France

Abstract. This paper stems from the fact that the topographic index used in TOPMODEL is not dimensionless. In each pixel i in a catchment, it is defined as xi=ln(ai/Si), where ai is the specific contributing area per unit contour length and Si is the topographic slope. In the SI unit system, ai/Si is in meters, and the unit of xi is problematic. We propose a simple solution in the widespread cases where the topographic index is computed from a regular raster digital elevation model (DEM). The pixel length C being constant, we can define a dimensionless topographic index yi=xi-lnC. Reformulating TOPMODEL equations to use yi instead of xi helps giving the units of all their terms and emphasizes the scale dependence of these equations via the explicit use of C outside from the topographic index, in what can be defined as the transmissivity at saturation per unit contour length T0/C. The term lnC defines the numerical effect of DEM resolution, which contributes to shift the spatial mean x of the classical topographic index when the DEM cell size C varies. A key result is that both the spatial mean y of the dimensionless index and T0/C are much more stable with respect to DEM resolution than their counterparts x and T0 in the classical framework. This shows the importance of the numerical effect in the dependence of the classical topographic index to DEM resolution, and reduces the need to recalibrate TOPMODEL when changing DEM resolution.

Publications Copernicus
Download
Citation
Share