Topographic Indices, NYC

Topographic indices calculated in support of Kelleher and McPhillips (in review). We calculated two topographic indices - absolute sink depth (m) and topographic wetness index (-) - using TauDEM (v. 5.3) software and the D-infinity flow routing algorithm.

Watersheds include those in Manhattan (CP1, CP2, M1, M2) and Staten Island (SI1, SI2). Naming convention and sites are shown in the associated manuscript. Note that processing for Baltimore is limited to the extent of each watershed that overlaps with the Baltimore city limits, though processing occurred for the entire watershed and was masked to this area.

Values were processed based on the LiDAR digital elevation models (DEM) for NYC, linked below in references (note: to make datasets comparable, the NYC DEM was coarsened to 0.91 m resolution). As presented in the associated manuscript, all topographic index values were extracted for all surfaces (e.g., bare soil, pavement, sidewalks, and vegetated areas) that excluded open water and building footprints (where topographic processing and DEM coverages are less reliable). Land cover datasets are linked below.

Naming convention for all files first specifies watershed name (NYC: cp1, cp2, m1, m2, si1, si2) followed by topographic index type (twi = topographic wetness index, sink = sink depth).

Descriptions for how each topographic index are calculated are specified in the associated manuscript. Generally, sink depths were calculated by differencing the filled and unfilled DEMs, and TWI was calculated from topographic slope and accumulated area, both processed within TauDEM (note: when negative slopes were calculated, these were replaced with very small values, e.g., 0.001).