Precipitation is the main component input of watershed in flood, water balance and water resources computation.
Any rainfall-runoff simulation of basin response by models needs the accurate amount of rainfall
over the basin. Therefore the simulation of spatial distribution of rainfall is an important factor. Measuring
rainfall in scattered point stations and generalizing it to arial extent often causes considerable errors. Such
source of error is one the most important in both rainfall-runoff simulation and continues hydrologic
process and water balance modeling. A number of methods of interpolation and extrapolation of rainfall
data has been developed which have some limitations and need to be evaluated accurately for finding the
most appropriate one based on specific local conditions. For the purpose of the research a wide range area
in the south west of Iran with about 258552 km
evaluated in regional homogeneity analysis. The results show that delineation of regional homogenity partly
improves the spatial distribution of rainfall. Another conclusion is that using estimated data for data
compellation has not improved the overall results.