starsExtra (version 0.2.8)

flowlength: Calculate flow length

Description

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.

Usage

flowlength(elev, veg, progress = TRUE)

Value

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

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

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)")
# }