Development of a Global Representative Hillslope Data Set for Use in Earth System Models

The development of a global data set consisting of a distributed set of geomorphic parameters suitable for use in a representative hillslope parameterization within an Earth System model (ESM) is described. An element of a representative hillslope is defined by six geomorphic properties: height above the stream channel, distance to the stream channel, width, slope, aspect, and area. The methodology employs spectral analysis to identify an appropriate spatial scale at which to resolve the stream network and catchments in an ESM gridcell. This objective method is applied to an ESM grid using a global high-resolution digital elevation model (DEM) as input. The resulting spatially varying length scales then determine the stream order used to delineate catchments from the DEM. The geomorphic parameters describing the representative hillslopes are obtained by discretizing the catchments into elements based on elevation and aspect, and then averaging the geomorphic properties within each element, resulting in a statistical representation of the hillslopes within the domain. The method is applied to a DEM having a spatial resolution of 3 arcseconds (about 90 $m$ at the equator) on a grid having approximately $1°$ spatial resolution.