flowAccumulation: 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 SpatRaster
flowAccumulation(x, weight=NULL, filename="", ...)

Value

SpatRaster

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

Author

Emanuele Cordano

Details

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

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/

Examples

Run this code

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)

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