This tool can be used to calculate the relative stream power (RSP) index. This index is directly related to the stream power if the assumption can be made that discharge is directly proportional to upslope contributing area (As; `sca`). The index is calculated as:

> RSP = Asp × tan(β)

where As is the specific catchment area (i.e. the upslope contributing area per unit contour length) estimated using one of the available flow accumulation algorithms; β is the local slope gradient in degrees (slope); and, p (`exponent`) is a user-defined exponent term that controls the location-specific relation between contributing area and discharge. Notice that As must not be log-transformed prior to being used; As is commonly log-transformed to enhance visualization of the data. The slope raster can be created from the base digital elevation model (DEM) using the slope tool. The input images must have the same grid dimensions.

## Reference

Moore, I. D., Grayson, R. B., and Ladson, A. R. (1991). Digital terrain modelling: a review of hydrological, geomorphological, and biological applications. Hydrological processes, 5(1), 3-30.

## See Also

sediment_transport_index, slope, `D8FlowAccumulation` `DInfFlowAccumulation`, `FD8FlowAccumulation`

## Function Signature

`def relative_stream_power_index(self, specific_catchment_area: Raster, slope: Raster, exponent: float = 1.0) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW