The calculation of inverse distance values is based on the equation
(22.4)
the weights are in this case defined by
(22.5) 
Where the index i refers to the station index and p is the power parameter taking on a positive value. The larger the power parameter value the more peaky the interpolated surface will be at the station values. Note that at the measurement locations the station value is always used.
The catchment wide weights used for the inverse distance method are
(22.6) 
where the catchment wide weight is then given by
(22.7) 
the evaluation of the above is done through a numerical integration using evenly distributed grid.
