Study of Spatial & Temporal Distribution of Precipitation and its Impacts on Transportation Systems in Iran

Recognition of weather events has great role in decreasing road accidents and road Maintenance costs. During recent years the role of atmospheric conditions in road safety, winter road maintenance and environmental impacts have been of great importance among researchers. Knowing the starting and ending time of snowfall is important in winter road maintenance management, safety acts of police, and more preparedness of drivers and all related to transportation systems. In this paper, based on statistics of 119 meteorological stations, we have determined probability of starting and ending of precipitation. Starting of snowfall in Iran depends on elevation, latitude and environmental factors, so that on Albors, Zagros, Khorasan and Azerbaijan mountainous regions, starting time of snowfall is usually November, however very high mountainous regions may have snowfall in October. Based on the map of distribution of special and temporal ending time of snowfall in most of mountainous regions, this event will be continued up to May. Therefore starting and duration of winter road maintenance in Iran would be determined based on analysis out puts. Finally may statistics in the country may be examined because of the importance of studying weather related road accidents (Road accidents accompanied by precipitation). In this research we have used road accidents statistics related to safety and traffic section of The Iranian Road and Transportation Organization in the period 1990 - 1998. Determining the spatial and temporal distribution of each effective factor in accidents are other objectives of this paper. As a result, the maximum number of road accidents in rainy conditions have occured in Fars, Kohkiloye va Boyer Ahmad and Hormozgan provinces. In snowy conditions most of road accidents have occured in Charmahal va Bakhtiyari, Zanjan and Tehran provinces.