عنوان مقاله [English]
Background and objectives: As a natural phenomenon, dust storm occurs in all climatic conditions, however, as a typical feature of arid and semi-arid climate, causes severe problems in infrastructures and activities of human society such as agriculture, transportation and industries. Dust storm is a phenomena that has a high frequency of occurrence in some parts of the world, especially in the Middle East. Dust storm occurrence in this region has been increased in the past decade, even in the humid months of the year. Studies on dust storms in Iran have shown that many environmental factors contribute to occurrence of this phenomenon and its long-term stability besides the natural factors. The objective of this study was to investigate the dust deposition rate during a one-year period, and its relationship with selected climatic and spatial factors, in Javanrood township.
Materials and methods: This study was carried out in an area of about 5500 hectares in Javanrood township, located in Kermanshah province. Since the beginning of August 2015 until the end of June 2016, dust samples were collected at the end of each season, from 35 sampling points randomly distributed throughout the township, including 21 points located in the urban and 14 points located in the rural areas. Dust deposition rate was calculated by dividing the mass of dust on the sampler surface and the sampling period. Dust deposition rate relationship with selected climatic parameters such as prevailing wind speed, wind direction, humidity, rainfall and mean temperature (provided by Meteorological Organization), and spatial parameters such as distance from the western border of the country (assuming that Iraq country is one of the dust resources in this region) and the elevation (above sea level) were examined using Pearson correlation test.
Results: The average rate of dust deposition was 0.38 gr m-2 day-1(1376 kg ha-1 year-1) in the study area. In terms of time, spring season had the highest rate of deposition with an average of 0.47 gr m-2 day-1, and summer had the lowest rate with an average of 0.26 gr m-2 day-1. Considering the spatial aspect, rural areas in winter had the highest rate of deposition with an average of 0.52 gr m-2 day-1, while, urban areas in summer had the lowest amount of deposition rate of 0.23 gr m-2 day-1 in average. Results indicated that the amount of dust deposition in the study area is higher than defined standard levels for most parts of the world. The dust deposition in the rural parts was greater than urban parts, probably because of the adjacency to the dust source areas. The dust deposition rate decreased with increasing in elevation. It had positive and significant correlations with direction and speed of wind (at p< 0.01 and 0.05, respectively) and negative correlations with humidity and rainfall means.
Conclusion: It seems that the differences among the values of dust deposition, were resulted from local dust events, the elevation differences, the distance from Iraq border, differences in sampling platforms height, and also adjacency to the farmlands and uncovered pastures. High levels of atmospheric dust deposition in the region and its relation with climatic factors, is probably due to the simultaneous effects of local and regional (which is created in neighboring countries and transported to the area) dust storm events.