# Upslope contributing area and wetness index calculation

### Description

Determine upslope contributing area based on an elevation raster and, optionally, compute the topographic wetness index.

### Usage

1 | ```
upslope.area(dem, log = TRUE, atb = FALSE, deg = 0.1, fill.sinks = TRUE)
``` |

### Arguments

`dem` |
Elevation raster (in m), using a projected coordinate system with identical x and y resolutions. |

`log` |
Return the natural log of the values. |

`atb` |
If TRUE, include both the upslope contributing area and the topographic wetness index |

`deg` |
Minimum intercell slope to identify with a sink (degrees). |

`fill.sinks` |
Fill sinks before calculation using the threshold angle given by deg. |

### Note

This is a wrapper to the function implemented in the TOPMODEL package by Wouter Buytaert.

### Author(s)

Peter Metcalfe and Wouter Buytaert

### References

Quinn, P. F., Beven, K. J., & Lamb, R. (1995). The In (a/tan/beta) index: How to calculate it and how to use it within the Topmodel framework. Hydrological processes, 9(2), 161-182.

### Examples

1 2 3 4 5 6 7 8 | ```
## Not run:
require(dynatopmodel)
data(brompton)
a.atb <- upslope.area(brompton$dem, atb=TRUE)
sp::plot(a.atb, main=c("Upslope area (log(m^2/m))", "TWI log(m^2/m)"))
## End(Not run)
``` |