Abstract––Local Interpolation and regional analyzing of rainfall are one of the important issues of Water Resources and Meteorology. There are several methods for this purpose. IDW is one of the classic methods for estimating precipitation. This method of interpolation at each point gives a weight to the distance to the reference point. IDW method has been modified in various ways in different research and new parameters such as elevation were added to it. This reform has two modes. The First state is the ratio of elevation to distance and the second is the inverse of multiplying elevation and distance. This paper has three objectives. First is generalizing the alignments of various elevation and distances in MIDW. Second is dimensionless the weights (separately and integrated) according to relationship that is used. Third is analyzing interpolation errors of daily rainfall regionally. Genetic algorithm is used to find optimal answers. Results showed that optimal answers primarily is depending on the reverse effects of multiply of altitude and distance (55%) and with a direct effect of altitude and inverse effect of distance (45%). It's then 71% of cases shows that integrated dimensionless yields better result than separately ones. Impacts of elevation were established in all MIDW methods. Results showed that this parameter should be used in interpolation of rainfall. Case study is a daily rainfall catchment of Mashhad plain.

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