| 英文摘要: | In Iran, one of the environmental issues is dust storms, especially in the west and the southwest. These storms are important factors in soil erosion, economic damage to industry, agriculture, transportation sectors, and human life. Therefore, the recognition of the frequency, occurrence probability, and the return period of these storms can be instrumental in reducing damages. The purpose of this study was the spatial analysis of the occurrence probability of dusty days in the west and southwest of Iran in April, May, June, and July, using the Markov chain. The daily dust data was used in 14 synoptic stations during 24 years (1990-2013). In this study, to detect dust storms, a horizontal visibility factor of <= 1000 m was used for all meteorological codes. At first, the days were divided into two groups of normal days and dusty days and then the frequency of matrices, probability of transmission, and the stable matrix were calculated. Finally, the spatial distribution of the occurrence probability and the return period of the dust within 2 to 5 days were depicted. The results showed that the average occurrence probability of 2-day dusts was 15% in April and May, 22% in June, and 24% in July. Also, the occurrence probability of 3-day dusts decreased to 4%, 8%, and 9%, respectively. The return period of 1-day dust in all stations of the area and all months was 1.25 day on average; however, due to the increase in the duration of the dust period, its return period increased exponentially. Spatial distribution of stable matrix also revealed that the occurrence probability of dust in the western and southeastern parts of the studied area was more than those of the others.
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