Spatial Analysis of Precipitation Variations in Middle Zagros Using Geo-Statistical Methods (1995-2004)

This study aims to describe and model the spatial variations of precipitation in the mountainous areas of middle Zagros using geo statistical techniques. To this aim, a dataset was obtained from 249 precipitation recording stations of Meteorological organization (climatologic, synoptic, and rain gauge) and Ministry of Energy of Iran in a 10-year period (1995-2004). Among these stations, 219 stations were used for modeling the spatial variability of precipitation, and the remaining 30 stations were used to evaluate the proposed method. To check the normality of data and detect the trend, Kolmogorov- Smirnov test and Trend Analysis of ESRI Arc GIS 9.3 is utilized, respectively. An evaluation of simple, ordinary, and general kriging with and without auxiliary variables of altitude, latitude, slope, and distance from ridges show that the ordinary kriging with latitude and distance from the ridge auxiliary variables are more precise. To illustrate the spatial variability of precipitation in the area of study, profiles of precipitation and altitudes perpendicular to ridges were plotted in the 50 Km intervals. These profiles make evidence that despite the relative correlation between precipitation and topography, the points with maximum precipitation does not correspond to the highest topographic points. Moreover, leeward and windward sides present different behaviors with respect to precipitation. Finally, it is found that topographies act as barriers in the way of air masses, thus air masses in clash with mountain release large amounts of their humidity.