Effects of DEM scale on the spatial distribution of the TOPMODEL topographic wetness index and its correlations to watershed characteristics
D. R. Drover1, C. R. Jackson2, M. Bitew2, and E. Du31Virginia Water Resources Research Center, Virginia Tech, Blacksburg, VA 24061, USA 2Warnell School of Forestry and Natural Resources, Univ. of Georgia, Athens, GA 30605, USA 3Climate Science Department, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
Received: 30 Jun 2015 – Accepted for review: 10 Sep 2015 – Discussion started: 12 Nov 2015
Abstract. Topographic wetness indices (TWIs) calculated from digital elevation models (DEMs) are meant to predict relative landscape wetness and should have predictive power for soil and vegetation attributes. While previous researchers have shown cumulative TWI distributions shift to larger values as DEM resolution decreases, there has been little work assessing how DEM scales affect TWI spatial distributions and correlations with soil and vegetation properties. We explored how various DEM resolutions (2, 5, 10, 20, 30, and 50 m) subsampled from high definition LiDAR altered the spatial distribution of TWI values and the correlations of these values with soil characteristics determined from point samples, Natural Resources Conservation Service (NRCS) soil units, depths to groundwater, and managed vegetation distributions within a first order basin in the Upper Southeastern Coastal Plain with moderate slopes, flat valleys, and several wetlands. Point-scale soil characteristics were determined by laboratory analysis of point samples collected from riparian transects and hillslope grids. DEM scale affected the spatial distribution of TWI values in ways that affect our interpretation of landscape processes. At the finest DEM resolutions, valleys disappeared as TWI values were driven by local microtopography and not basin position. Spatial distribution of TWI values most closely matched the spatial distribution of soils, depth to groundwater, and vegetation stands for the 10, 20, and 30 m resolutions. DEM resolution affected the shape and direction of relationships between soil nitrogen and carbon contents and TWI values, but TWI values provided poor prediction of soil chemistry at all resolutions.
Drover, D. R., Jackson, C. R., Bitew, M., and Du, E.: Effects of DEM scale on the spatial distribution of the TOPMODEL topographic wetness index and its correlations to watershed characteristics, Hydrol. Earth Syst. Sci. Discuss., 12, 11817-11846, doi:10.5194/hessd-12-11817-2015, 2015.