A non‐isotropic gauge interpolation scheme applied to the montreal rainstorm of 14 July 1987

Abstract Raingauge data from the 14 July 1987 rainstorm over Montreal are used to underline the reduced errors obtained with a non‐isotropic interpolation scheme. This scheme modifies the geometrical distance between a point and a set of gauges on the basis of the orientation and elongation of the surface rainfall pattern. Initial guesses of these two parameters can be obtained from the two‐dimensional autocorrelation pattern of radar‐derived maps of surface rainfall. The set of optimum parameters can also be derived from raingauge data only by computing error statistics obtained from the successive omission of one gauge from the available network. The RMS error of 18% is significantly better than that of 26% obtained with isotropic interpolation. Results from data on this day also reveal that RMS errors are relatively insensitive to the functional relationship between the weights of the optimum number of gauges and the distance to a given point. The orientation and elongation of a rainfall pattern is of ...