High-resolution global topographic index values for use in large-scale hydrological modelling
Marthews, T. R.
Dadson, S. J.
Modelling land surface water flow is of critical importance for simulating
land surface fluxes, predicting runoff and water table dynamics and for many
other applications of Land Surface Models. Many approaches are based on the
popular hydrology model TOPMODEL (TOPography-based hydrological MODEL), and the most important parameter of this
model is the well-known <i>topographic index</i>. Here we present new, high-resolution parameter
maps of the topographic index for all ice-free land pixels calculated from
hydrologically conditioned HydroSHEDS (Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales) data using the GA2 algorithm (GRIDATB 2). At
15 arcsec resolution, these layers are 4 times finer than the resolution
of the previously best-available topographic index layers, the compound
topographic index of HYDRO1k (CTI). For the largest river catchments
occurring on each continent we found that, in comparison with CTI our
revised values were up to 20% lower in, e.g. the Amazon. We found the
highest catchment means were for the Murray–Darling and Nelson–Saskatchewan
rather than for the Amazon and St. Lawrence as found from the CTI. For the
majority of large catchments, however, the spread of our new GA2 index values
is very similar to those of CTI, yet with more spatial variability apparent
at fine scale. We believe these new index layers represent greatly improved
global-scale topographic index values and hope that they will be widely used
in land surface modelling applications in the future.