Calculate flow length — flowlength • starsExtra

Calculates flow length for each pixel in a Digital Elevation Model (DEM) raster. Inputs and output are rasters of class stars, single-band (i.e., only `"x"` and `"y"` dimensions), with one attribute.

flowlength(elev, veg, progress = TRUE)

Arguments

elev: A numeric stars raster representing a Digital Elevation Model (DEM).
veg: A matching logical stars raster representing vegetation presence. TRUE values represent vegetated cells where flow is absorbed (i.e. sinks), FALSE values represent cells where flow is unobstructed.
progress: Display progress bar? The default is TRUE

Value

A numeric stars raster where each cell value is flow length, in resolution units.

References

The algorithm is described in:

Mayor, A. G., Bautista, S., Small, E. E., Dixon, M., & Bellot, J. (2008). Measurement of the connectivity of runoff source areas as determined by vegetation pattern and topography: A tool for assessing potential water and soil losses in drylands. Water Resources Research, 44(10).

Examples

# Example from Fig. 2 in Mayor et al. 2008

elev = rbind(
  c(8, 8, 8, 8, 9, 8, 9),
  c(7, 7, 7, 7, 9, 7, 7),
  c(6, 6, 6, 6, 6, 5, 7),
  c(4, 5, 5, 3, 5, 4, 7),
  c(4, 5, 4, 5, 4, 6, 5),
  c(3, 3, 3, 3, 2, 3, 3),
  c(2, 2, 2, 3, 4, 1, 3)
)
veg = rbind(
  c(TRUE,  TRUE,  TRUE,  TRUE,  FALSE, FALSE, TRUE),
  c(TRUE,  TRUE,  TRUE,  TRUE,  TRUE,  FALSE, FALSE),
  c(FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE),
  c(FALSE, TRUE,  FALSE, FALSE, FALSE, FALSE, TRUE),
  c(TRUE,  TRUE,  FALSE, FALSE, FALSE, FALSE, FALSE),
  c(TRUE,  TRUE,  TRUE,  FALSE, FALSE, FALSE, FALSE),
  c(FALSE, TRUE,  TRUE,  FALSE, FALSE, TRUE,  TRUE)
)
elev = matrix_to_stars(elev)
veg = matrix_to_stars(veg)

# Calculate flow length
fl = flowlength(elev, veg, progress = FALSE)

# Plot
plot(
  round(elev, 1), text_values = TRUE, breaks = "equal", 
  col = terrain.colors(6), main = "input (elevation)"
)

plot(
  veg*1, text_values = TRUE, breaks = "equal", 
  col = rev(terrain.colors(2)), main = "input (vegetation)"
)

plot(
  round(fl, 1), text_values = TRUE, breaks = "equal", 
  col = terrain.colors(6), main = "output (flowlength)"
)

# \donttest{
# Larger example
data(carmel)
elev = carmel
elev[is.na(elev)] = 0
veg = elev > 100
fl = flowlength(elev, veg, progress = FALSE)
plot(fl, breaks = "equal", col = hcl.colors(11), main = "flowlength (m)")

# }