One of the most important factors in natural resources researches is the depth of precipitation, especially its regional average. There are different methods for estimating the depth of precipitation such as Thiessen, arithmetic mean etc. These methods are simple and applicable, however since they do not consider spatial location and arrangement of data are not precise. Another method for preparing the isohytal maps is geostatistical approach. That is more precise and preferable precipitation gradient. In this study we used 30-years precipitation data from 52 stations. After normalizing of data and variogram analysis, three different methods, kriging, co-kriging, and weighing moving average (WMA) were used. Altitudes data were used as an auxiliary factor, in co-kriging. Cross- validation technique was used for comparison of these methods. Variographic analysis demonstrates suitable spatial elevation. The result showed that kriging method is more precise than WMA in this region. Finally, the precise spatial isohytal map is created by Kriging method. This map shows that the rainfall values extremely increased from east to the west of Mazandaran province.
