عنوان مقاله [English]
Background and objectives: In the recent decades dust storms have become serious natural hazards in the world. Although dust storms have been investigated in various aspects variation in wind speed and visibility and the frequency of dust storms requires more investigation. In this study, diurnal, monthly and yearly variation of parameters including wind speed, visibility and PM10 (particulate matter 10 micrometers or less in diameter) and frequency of dust storms is studied in the Sistan region for the twenty seven-year period.
Materials and methods: The Sistan in the southeast part of Iran is considered as the study area. Sistan has an arid and semi-arid climate with very low precipitation (59 mm) and air humidity and high evaporation (nearly 4820 mm) and annual temperature (22°C). To analysis the diurnal, monthly and yearly variation of wind speed and visibility, the collected data at the Zabol meteorological station were obtained from the Iran Meteorological Organization for study period. DDI (Dusty Days Index; the days with wind speed more than 15 m/s and visibility less than 1000 m) and DSI (Dusty Index) were applied in this study to analysis the monthly and yearly frequency of dust storms during 1991-2018. Furthermore, the hourly concentration of PM10 was received from the meteorological and environmental stations of the respective centers during 2013-2018.
Results: The results show similar diurnal, monthly and yearly patterns of wind speed, visibility and PM10 variation in all months during study period. The highest PM10 concentration and lowest visibility were observed at 10:30 am in accords with highest wind speed. The lowest PM10 and highest visibility occurred at 7:30 pm in accord with lowest wind speed. The greatest values of DDI, DSI and PM10 were observed in June. Furthermore, the greatest values of DDI, DSI and PM10 were observed in 2001 during study period. The period of 1999-2004 is dusty than the periods of 1990-1999 and 2005-2018 as DSI is 14, 174 and 66 days respectively. A strong correlation was observed between wind speed and visibility, wind speed and PM10 concentration and, visibility and PM10. These result show that either PM10 concentration or visibility depend on wind speed. Furthermore, a positive relationship was observed between PM10 and DSI and DDI.
Conclusion: In stud period, the Sistan region is dusty than other regions of Iran due to having greater frequency and intensity of dust storm. As the dustiness of Sistan is highly dependent on the situation of Hamoun lake, lake recovery is critical to reduce the intensity and frequency of dust storms.