Dust storm frequency after the 1999 drought in the Sistan region, Iran

Sustained drought and reduced precipitation in the Sistan region, Iran, has dried the Hamoun Lake and local vegetation, significantly reducing ground cover. These conditions have premitted strong wind erosion on already susceptible land. Analysis of data collected from the synoptic station in Zabol from 1999 to 2004 revealed that after 1999 the total number of dust storm events (DST) increased considerably, Accordingly, the number of hours of dusty air and the Dust Storm Index (DSI) have increased and horizontal visibility has decreased. Increasing DST and DSI values and decreasing horizontal visibility are indicators of dustiness in the region, The highest DST and DSI values-74 and 149 d, respectively-were observed in 2001. The indexes were higher in July and August every year. Additionally, a relationship was observed between increasing DST and DSI, drought occurrence and wind speed. Drought occurrence, an increase in wind speed and Lake Hamoun dryness have severely intensified dustiness in the region.