For each pressure X an MSAX map is calculated by applying the cause-effect relationship to the appropriate input map. These calculations are done for the existing water bodies according to the Global Lakes and Wetlands Database. Assuming no interaction among the drivers, for each water type in a grid cell, GLOBIO calculates the overall MSAi value by multiplying the MSAX values per (set of) drivers:
where i is a grid cell, MSAi is the overall value for grid cell i, MSAXi is the relative mean species abundance corresponding to the drivers LU (catchment land use and eutrophication) and CH (change in hydrological regime).
The MSA values for the different water types (lakes, rivers and wetlands) are aggregated per grid cell according to their relative area.
To obtain the MSAr of a region, GLOBIO calculates the area weighted mean of MSAi values of all relevant grid cells.
where Ai is the surface water area of grid cell i.
The relative contribution of each driver to a loss in MSA may be calculated from formulas 1 and 2.