Hi @leige ,
Well actually I don’t think so. The parameter that represents intensity should be i_rxy, not r_y.
i_rxy represents the relative impact of each threat. Search for “The impact of threats on habitat in a grid cell is mediated by four factors.” in the User’s Guide to find a run down.
I personally think that in this formula, r_y may be used to emphasize the threat.To be clear, it should always be equal to 1, rather than floating between 0 and 1.
Threat values from threat rasters can be values of presence, absence (0,1) or on a scale of intensity using floating point values from 0 to 1. From the User’s Guide:
Each threat source needs to be mapped on a raster grid. A grid cell value on a threat’s map can either indicate intensity of the threat within the cell (e.g., road length in a grid cell or cultivated area in a gird cell) or simply a 1 if the grid cell contains the threat in a road or crop field cover and 0 otherwise. …
All mapped threats should be measured in the same scale and metric. For example, if one threat is measured in density per grid cell then all degradation sources should be measured in density per grid cell where density is measured with the same metric unit (e.g., km and km2). Or if one threat is measured with presence/absence (1/0) on its map then all threats should be mapped with the presence/absence scale.
The right side of the equation
r_y * i_rxy * beta_x * S_jr is the threat raster pixel value
r_y adjusted by the impact score for the threat, the beta score for accessibility (protected), and the sensitivity of the habitat to the threat.
Why is the z value set to 2.5?
Good question, I bet this has been addressed on the forums before. I’ll try and search for it.
According to the formula, D _xj represents the total threat level of all rasters of all threats to x raster. That being the case, is it possible in theory to exceed 1?
From the Users’s Guide:
Also note that threat weights are normalized so that the sum across all threats weights equals 1.