flowAccumulation: Flow accumulation

In terra: Spatial Data Analysis

Flow accumulation

Description

Computes flow accumulation or the total contributing area in terms of numbers of cells upstream of each cell.

Usage

## S4 method for signature 'SpatRaster'
flowAccumulation(x, weight=NULL, filename="", ...) 

Arguments

x	SpatRaster with flow direction, see terrain.
weight	SpatRaster with weight/score daa. For example, cell area or precipitation
filename	character. Output filename
...	additional arguments for writing files as in writeRaster

Details

The algorithm is an adaptation of the one proposed by Zhou at al, 2019.

Value

SpatRaster

Author(s)

Emanuele Cordano

References

Zhou, G., Wei, H. & Fu, S. A fast and simple algorithm for calculating flow accumulation matrices from raster digital elevation. Front. Earth Sci. 13, 317–326 (2019). doi:10.1007/s11707-018-0725-9. Also see: https://ica-abs.copernicus.org/articles/1/434/2019/

See Also

terrain,watershed, NIDP

Examples

elev1 <- array(NA,c(9,9))
elev2 <- elev1
dx <- 1
dy <- 1 
for (r in 1:nrow(elev1)) {
  y <- (r-5)*dx
  for (c in 1:ncol(elev1)) {
    
    x <- (c-5)*dy
    elev1[r,c] <- 5*(x^2+y^2)
    elev2[r,c] <- 10+5*(abs(x))-0.001*y 
  }
} 


## Elevation raster
elev1 <- rast(elev1)
elev2 <- rast(elev2)

t(array(elev1[],rev(dim(elev1)[1:2])))
t(array(elev2[],rev(dim(elev2)[1:2])))

plot(elev1)
plot(elev2)

## Flow direction raster
flowdir1<- terrain(elev1,v="flowdir")
flowdir2<- terrain(elev2,v="flowdir")

t(array(flowdir1[],rev(dim(flowdir1)[1:2])))
t(array(flowdir2[],rev(dim(flowdir2)[1:2])))

plot(flowdir1)
plot(flowdir2)

## 
flow_acc1 <- flowAccumulation((flowdir1))
flow_acc2 <- flowAccumulation((flowdir2))

weight <- elev1*0+10

flow_acc1w <- flowAccumulation(flowdir1,weight)
flow_acc2w <- flowAccumulation(flowdir2,weight)

t(array(flow_acc1w[],rev(dim(flow_acc1w)[1:2])))
t(array(flow_acc2w[],rev(dim(flow_acc2w)[1:2])))

plot(flow_acc1w)
plot(flow_acc2w)


## Application wth example elevation data

elev <- rast(system.file('ex/elev.tif',package="terra"))
flowdir <- terrain(elev,"flowdir")

weight <- cellSize(elev,unit="km")
flowacc_weight <- flowAccumulation(flowdir,weight)
flowacc  <- flowAccumulation(flowdir)

terra documentation built on Oct. 14, 2024, 5:07 p.m.