Statistical Analysis of Frost Temperatures with Risk Management Road Frost Approach in Lorestan & Chaharmahal o Bakhtiyari Provinces

In order to analyze the frost temperatures of the central Zagros in the Lorestan and Chaharmahal regions, the daily minimum temperatures of 14 weather stations were obtained from the Meteorological Organization of Iran. The mean dates of the beginning, ending, and length of the frost period were calculated for each station. The frequency and duration of different frost periods (1, 2 and over 7 days) were calculated. The results showed that the frost period begins in the northern and mountainous parts of the study area earlier than the southern parts and the lowlands. The length of the frost period showed the same behavior. Although the frost period begins at the same time in both the north of Lorestan and the east of Chaharmahal, but the mountainous nature of the eastern Chaharmahal postponed the end of the frost period. The frost period frequencies with different intensities were higher in the mountainous parts. Especially the frequency of days with zero to -10 degrees Celsius was remarkable. The variability of the beginning date was much higher the variability of the ending date, especially in the mountainous areas. Findings of the study demonstrate the necessity of the installation of road weather stations and weather watching instruments in the mountainous parts of the study area.