Assessment the efficiency of 6 interpolation methods for estimation of annual rainfal stations using Geography Information System (GIS): (A case study on 21 rainfalls station in Golestan province, Iran)

Precipitation is one of the most important entrance parameters of a watershed basin. Concentrated (point) rainfall measurements, unsuitable dispersion of rainfall stations and also lack of connection roads to some of areas for measurements, cause that the interpolation for some areas become essential. The field statistical methods because of consideration to stations situation and spatial correlation, it can be suitable but there are some limitation because of insufficient data. In this study in order to assessment of efficiency of different interpolation methods for estimation of rainfall stations without data in north of Iran, 21 rainfall station with yearly rainfall data were selected, while 4 stations were choose as evidences. In next step in Ilwis version 3.1, according to the 17 stations (except 4 evidence stations) data for each 4 evidence rainfall stations was created for Golestan province, in this step for interpolation, 6 methods were applied as follows: Nearest Point 'Universal Kriging' Kriging 'Moving Surface' Moving Average and Trend Surface. Finally the estimated value for 4 evidence stations compared with the evidence data (recorded data). The assessments showed that Universal Kriging method had the least error in comparison with the other methods in this case.