ABSTRACT A variety of landscape properties have been modeled successfully using topographic indices such as topographic wetness index (TWI), defined as ln(a/tanβ), where a is the specific upslope area and β is the surface slope. In this study, 25 m spatial resolution from digital elevation models (DEM) data were used to investigate the scale-dependency of TWI values when converting DEMs to 50 and 100 m. To investigate the impact of different spatial resolution, the two lower resolution DEMs were interpolated to the original 25 m grid size. In addition, to compare different flow-direction algorithms, a second objective was to evaluate differences in spatial patterns. Thus the values of TWI were compared in two different ways: 1) distribution functions and their statistics; and 2) cell by cell comparison of DEMs with the same spatial resolution but different flow- directions. As in previous TWI studies, the computed specific upstream is smaller, on average, at higher resolution. TWI variation decreased with increasing grid size. A cell by cell comparison of the TWI values of the 50 and 100 m DEMs showed a low correlation with the TWI based on the 25 m DEM. The results showed significant differences between different flow-diretction algorithms computed for DEMs with 25, 50 and 100 m spatial resolution.
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nullA. Ruhoff, N. Castro and A. Risso, "Numerical Modelling of the Topographic Wetness Index: An Analysis at Different Scales," International Journal of Geosciences, Vol. 2 No. 4, 2011, pp. 476-483. doi: 10.4236/ijg.2011.24050.
 J. P. Wilson and J. C. Gallant, “TAPES-G: A Grid-Based Terrain Analysis Program for the Environmental Sci- ences,” Computers e Geosciences, Vol. 22, No. 7, 1996, pp. 713-722.
 J. Blaszcynski, “Landform Characterization with GIS,” Photogrammetric Engineering and Remote Sensing, Vol. 63, 1997, pp. 183-191.
 J. R. Eastman, “Idrisi Andes—Guide to GIS and Image Processing,” Clark University, Worcester, 2006..
 J. Schauble, “Hydrotools for Arcview,” Institute of Applied Geosciences, Technical University of Darmstadt, Darmstadt, 2000.
 S. K. Jenson and J. O. Domingue, “Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis,” Photogrammetric Engineering and Remote Sensing, Vol. 54, 1988, pp. 1593-1600.
 D. G. Tarboton, R. L. Bras and I. Rodriguez-Iturbe, “On the Extraction of Channel Networks from Digital Elevation Data,” Hydrological Processes, Vol. 5, No. 1, 1991, pp. 81-100. doi:10.1002/hyp.3360050107
 O. Planchon and F. Darboux, “A Fast, Simple and Versatile Algorithm to Fill the Depressions of Digital Elevation Models,” Catena, Vol. 46, No. 2-3, 2001, pp. 159-176.
 K. J. Beven and M. J. Kirkby, “A Physically Based Variable Contributing Area Model of Basin Hydrology,” Hydrological Sciences Bulletin, Vol. 24, No. 1, 1979, pp. 43-69. doi:10.1080/02626667909491834
 I. D. Moore, R. B. Grayson and A. R. Ladson, “Digital Terrain Modelling: A Review of Hydrological, Geomorphological, and Biological Applications,” Hydrological Processes, Vol. 5, No. 1, 1991, pp. 3-30.
 J. P. Wilson and J. C. Gallant, “Terrain Analysis: Principles and Applications,” John Wiley & Sons Inc., New York, 2000.
 S. Kienzle, “The Effects of DEM Raster Resolution on First Order, Second Order and Compound Terrain Derivates,” Transactions in GIS, Vol. 8, No. 1, 2004, pp. 83- 111. doi:10.1111/j.1467-9671.2004.00169.x
 M. S. Horritt and P. D. Bates, “Predicting Floodplain Inundation: Raster-Based Modelling versus the Finite- Element Approach,” Hydrological Processes, Vol. 15, No. 5, 2001, pp. 825-842. doi:10.1002/hyp.188
 A. Gunter, J. Seibert and S. Uhlenbrook, “Modeling Spatial Patterns of Saturated Areas: An Evaluation of Different Terrain Inideces,” Water Resources Research, Vol. 40, 2004, pp. 1-19.
 R. Sorensen and J. Seibert, “Effects of DEM Resolution on the Calculation of topographical indices: TWI and Its Components,” Journal of Hydrology, Vol. 347, No. 1-2, 2007, pp. 79-89. doi:10.1016/j.jhydrol.2007.09.001
 N. M. R. Castro, A. V. Auzet, P. Chevallier and J. C. Leprun, “Land Use Change Effects on Runoff and Erosion from Plot to Catchment Scale on the Basaltic Plateau of Southern Brazil,” Hydrological Processes, Vol. 13, No. 11, 1999, pp. 1621-1628.
 A. L. O. Borges and M. P. Bordas, “Escolha de Bacias Representativas e Experimentais Para o estudo da eros?o no Planalto Basáltico Sul-Americano,” Congresso brasileiro e encontro nacional de pesquisa sobre conserva??o do solo, Londrina, 1990.
 N. M. R. Castro, “Ruissellement et érosion sur des bassins versants de grande culture du plateau basaltique du sud du Brésil (Rio Grande do Sul),” Tese (Doutorado), Université Louis Pasteur, Strasbourg, 1996.
 P. Chevallier, “As precipita??es na regi?o de Cruz Alta e Ijuí (RS-Brasil),” Caderno de Recursos Hídricos, Vol. 24, 1991, pp. 1-24
 M. Eineder, A. Roth, R. Bamler and B. Rabus, “The Shuttle Radar Topography Mission—A New Class of Digital Elevation Models Acquired by Spaceborne Radar,” ISPRS Journal of Photogrammetry e Remote Sensing, Vol. 57, No. 4, 2003, pp. 241-262.
 J. F. O’Callaghan and D. M. Mark, “The Extraction of Drainage Networks from Digital Elevation Data,” Computer Vision, Graphics, and Image Processing, Vol. 28, 1984, pp. 328-344.
 P. F. Quinn, K. J. Beven and R. Lamb, “The ln(a/tanβ) Index: How to Calculate it and How to Use it within the Topmodel Framework,” Hydrological Processes, Vol. 9, No. 42, 1995, pp. 161-182. doi:10.1002/hyp.3360090204
 D. G. Tarboton, “A New Method for the Determination of Flow Directions and Upslope Areas in Grid Digital Elevation Models,” Water Resources Research, Vol. 33, No. 2, 1997, pp. 309-319. doi:10.1029/96WR03137
 C. A. Onstad and D. L. Brakensiek, “Watershed Sim- ulation by the Stream Path Analogy,” Water Resources Research, Vol. 4, No. 5, 1968, pp. 965-971.
 C. D. Renno, “Sistema de análise e simula??o hidrológica aplicado a bacias hidrográficas,” Tese (Doutorado em Sensoriamento Remoto), Instituto Nacional de Pesquisas Espaciais, S?o José dos Campos, 2003.