Received: 15 May 2011, Reviewed: 19 May 2011, Revised: 21 May 2011, Accepted: 26 May 2011 Estimating the Real Capacity of Rain Erosion Using GIS (The Fournier Case Study for Isfahan) A, Gandomkar Najafabad Branch, Islamic Azad University, Najafabd, Iran aagandomkar@yahoo.com Interpolation, the generalization of point data to scatter data, and combining maps are three cases of important applications of GIS. In this study, it has been tried to make the estimation of rain erosion capacity (Fournier Method) more real through using GIS capability in interpolation and the generalization of point data to scatter data. In Fournier method, the rain erosion capacity is calculated through the use of two climatic parameters (annual precipitation and the rainfall mean in the rainiest month of year) and two physiological parameters (the height and slop of the region). The findings of this study indicated that there is significant difference between these two methods of calculating rain erosion capacity. Using the means of rain erosion potential was estimated to be almost 3.4 tones per square kilometers annually while this amount was estimated to be 4.5 tones per square kilometers annually by using GIS capabilities. [Amir Gandomkar, Estimating the Real Capacity of Rain Erosion Using GIS (The Fournier Case Study for Isfahan). International Journal of Agricultural Science, Research and Technology, 2011; 1(1):33-38]. Keywords: Interpolation, Point data, Scatter data, Rain erosion capacity 1. Introduction One of the problems that researchers of geomorphology-climatology and civil are met in city planning, is estimating the real amount of the rain deposition, because in some cases complex factors should be computed which their assessment is difficult, time consuming and expensive. There are more than 90 methods to estimate deposition square of an area which is different in accordance with the type of the deposition in used elements (Gandomkar, 2000). Douglas's Method, Musgrave's Method (1947) and Fournier's Method (1960) are some common examples of estimating deposition. These models have used some limited factors which are quite simple to obtain or evaluate. In some other methods, various factors are used, such as: USLE Method (Wishmayer 1947), EMP Method (Yaroslov Serni 1952), Fao Method, Estlic Method (Zashar 1982), Psiac Method (PSIAC) and SLEMSA Method (Ramesht, 1996). Fournier's Method (1960) estimates amount of annual deposition of an area with respect to climatic and morphologic specialties. In this method, two climatic parameters (average annual precipitation and rainfall mean in the rainiest month of year) and two physiological parameters (The height and slope of the region) are used to compute the square of the rain erosion capacity as following (Chorley and et al, 1985). Equation(1): 1.56 - tanS) H (0.46Log P 2.65Log Log 2 s Q × + = ρ H : Average height of the region according to meter S: Average slope of the region according to degree P: Average annual precipitation according to mm Qs: Deposition according to ton in square kilometer in a year ρ 2 : Rainfall mean in the rainiest month of year according to mm (Rafahi, 1999). Fournier studied floating deposition weight for 78 arid or semi arid areas in Tunisia and Algeria which had a survey from 2460 to 1060000 square kilometer. He showed that there's a meaningful relationship between the deposition weight and regard monthly rain to average annual ( P 2 ρ ) in areas which have different unevenness. In this relation, p is the average annually precipitation according to mm and ρ 2 is the Rainfall mean in the rainiest month of year according to mm. So it's clear that in arid and semi arid areas which most precipitation of a year happens in one or two special International Journal of Agricultural Science, Research and Technology Available online on: www.ijasrt.com Abstract