Topography, Hydrology, & Soils

The WSRRI spatial priorities were directly and indirectly derived using a variety of datasets pertaining to the physical environment, including data on topography, hydrology, and soils. Though these geophysical features change over geological timespans, for our purposes they are considered to be static, so unlike the remote sensing, climate and infrastructure data, they are not updated every year.

The topographic and hydrological indices we used are all based on a digital elevation model (DEM) that represents the elevation at the surface of the Earth. We use the GLO-30 30m resolution DEM developed by the European Space Agency and hosted in the Google Earth Engine data repository (see entry in the catalog here).

From the DEM, we calculated various topographic indices in Google Earth Engine, including:

• slope

• aspect

• Heat Load Index (McCune and Keon, 2002)

• Topographic Position Index (Weiss, 2001)

• height above nearest drainage (Nobre et al., 2011)

• horizontal and vertical terrain curvature (Florinsky 2016)

In addition to the above topographic indices, we calculated the following additional indices using SAGA GIS version 9.0:

• multiresolution valley bottom flatness

• Topographic Wetness Index

• flow accumulation

• surface area

• texture

• ruggedness

• Morphometric Protection Index

Soil data used by TerrAdapt comes from SoilGrids.org, which developed a global 250m resolution soils dataset (we use version 2.0). From this dataset, we used the following variables, all calculated at a soil depth of 0-30 cm:

• percent clay content

• percent sand content

• percent silt content

• bulk density

• pH

• soil organic carbon

• soil order