usle

Universal Soil Loss Equation

The usle.py script in this directory calculates the average anual soil loss, using the USLE equation. The goal is to show off how the LUE framework can be used to perform the necessary calculations. Given enough hardware, LUE will perform the calculations in parallel. For very large problem sizes, LUE can use multiple distributed cooperating processes. There is no need to change the usle.py script for that. See usle-desktop.sh for an example of running the script on a single computer.

Note how the statement for calculating the anual soil loss in usle.py matches the one from the literature:

$$A = R \times K \times L \times S \times C \times P$$

With:

• $A$: Long-term average annual soil loss
• $R$: Rainfall erosivity factor
• $K$: Soil erodibility factor
• $L$: Topographic factor: slope length
• $S$: Topographic factor: slope gradient
• $C$: Cropping management factor
• $P$: Conservation practices factor

In usle.py, various kinds of operations are combined:

• Local operations, in which a new value for an output raster cell depends on one or more input raster cells at the same location in space. Examples: divide, multiply.
• Focal operations, in which a new value for an output raster cell depends on a neighbourhood of cells around an input raster cell at the same location in space. Example: slope.
• Flow direction network operations, in which a new value for an output raster cell depends on raster cells that can be reached via the flow direction network. Example: accu_threshold.

Whenever useful and possible, LUE schedules calculations from multiple operations for execution at the same time.

See also:

• https://en.wikipedia.org/wiki/Universal_Soil_Loss_Equation

Digital elevation model from Land Tirol - data.tirol.gv.at, licensed according to CC BY 4.0