An investigation into climatic and terrestrial drivers of dust storms in the Sistan region of Iran in the early twenty-first century.

Dust storms cause a wide range of impacts on environment, economy and human health in the Sistan region of southeastern Iran. This paper investigates long-term variability of dust activity over 23 years (1997-2019) using the Dust Storm Index (DSI) and the frequency of dust-storm days (DSD, visibility <1000 m) and assesses the associated importance of various terrestrial and climatic drivers. A dust storm corridor was identified, based on the prevailing wind direction at Zabol, including parts of the Hamoun lakes and surrounding desert in order to study the effects of vegetation cover and lake water levels on dust activity. The results show maximum intensity of dust storms occurred at 10:30 a.m. and in the summer, consistent with the highest wind speeds - associated with the regionally important Levar wind - and highest air temperatures and lowest precipitation and relative humidity. Strong positive correlations were demonstrated between DSI and wind speed, particularly in summer. The 2000-2004 period saw severe dust-raising activity with a DSI of 530.6. Mean wind speeds were greater and precipitation, humidity, vegetation and water coverage were lower during this severe dust-activity period than in other periods. Comparing 2000-2004 with 1997-1999, DSI was five times higher and DSD eight times higher. The dust storms with the longest duration occurred in July 2001 and June 2008 (114 h and 78 h respectively). The July 2001 event, in which wind speed peaked at 25 m/s and visibility dropped to 100 m on several occasions, may be the longest continuous dust storm on record. The key role of water and vegetation cover in the Hamouns was highlighted, indicating the importance of protecting the Hamoun ecosystems and sustainably managing their water resources in efforts to mitigate dust storm hazards in the Sistan region.