Spatial and temporal variations in the incidence of dust events over Iran

Dust events are natural hazards that frequently occur in many regions of Iran. The frequency of different categories of dust events over Iran during the period 1987–2016 and the first and second half of this period is analysed using visibility and the present weather data of 44 synoptic stations across Iran. These categories include dust in suspension, blowing dust, dust storm, severe dust storm and widespread dust. The frequency of dust events over Iran is calculated based on analysis of the three-hour-interval dataset of the synoptic stations and represented on a daily basis. Only one report in each day is enough to consider it as a dust event. Results indicated that the frequency of dust in suspension is extremely high over south-western and western Iran, while Zabol in eastern Iran has experienced the most frequent blowing dust and dust storm phenomena. In terms of seasonal variation of dust activity over different regions of Iran, the maximum and minimum frequency of dust events is observed in summer and winter, respectively. The frequency of dust phenomena during 1987–2001 is also compared against that during 2002–2016. It is found that the frequency of dust in suspension in most regions of Iran is significantly increased in the second period, particularly in western and south-western Iran. This implies that transport of dust towards western and south-western Iran has significantly increased in recent years. The frequency of blowing dust is also significantly increased in south-western Iran in 2002–2016 compared to that in 1987–2001, while changes in the frequency of blowing dust over Zabol in these two periods are negligible. The frequency of widespread dust is also analysed, and it is found that it only occurred over western and south-western Iran, with a much higher frequency during 2002–2016 than that of 1987–2001.