Spatial Analysis and Zoning Climatic Hazards of Threshold Rainfall Indicator in Road Network of Iran Using GIS

In this study¡ daily rainfall data of 95 synoptic stations of the country were used in a 18-year statistical period (1990-2007) in order to determine spatial – temporal distribution and zoning severity of risk degree of rainfall event in road transport network of the country. In addition¡ Spline with Barrier Interpolation Method was also used in this study by Critical Threshold Indicators in Arc GIS environment (rainfall with severity of 30mm and more¡ rainfall exceeding 90 percent and coefficient of variability of daily rainfall). The results show that maximum risk degree of spatial distribution and frequency of severity of rainfall can be observed in west-part roads of the Caspian region and central and northwest part of mountainous region of the country. In the same direction¡ maximum frequency of threshold rainfall severity is related to the main roads of cities of Anzali (304 days)¡ Kuhrang (277 days) and Rasht (210 days). In the same direction¡ maximum risk of temporal distribution of rainfall severity is observed in January (In Day month especially in southwest regions of the country) and March (April month in west regions of the country) in monthly scale in main roads network. The maximum coefficient of rainfall changes is observed in southeast regions of the country and maximum rainfall share exceeding 90 percent of total annual rainfall in the country is seen in west region of the country and also in west part of northern region.