Temporal variations in the frequency and concentration of dust events over Iran based on surface observations

Abstract

Using surface meteorological records of a 20-year period from 1991 to 2010, temporal variations in the frequency and concentration of transported dust events over Iran are investigated. Five regions of frequent dust events are identified. In the order of importance, these areas are the Khuzestan Plain, the coastal plain of the Persian Gulf, west of Iran, Tabas and Sistan. The first three areas create a belt of high frequency of dust events along the western foothills of the Zagros Mountains. The Khuzestan Plain is the area with the highest frequency of dust events, over which dust laden air is almost permanently present in summer, while the coastal plain of the Persian Gulf is the second most affected area. These two areas, along with west of Iran, are mostly influenced by transported dust from sources outside of Iran, while Tabas and Sistan are mostly influenced by arid lands in the interior of Iran. In contrast, the southern coastal strip of the Caspian Sea is the area with the least frequent dust episodes. Throughout Iran, the frequency of dust events strengthens in spring, peaks in summer and significantly weakens in autumn and winter, with the least observed frequency in winter. Significant monthly variations of the frequency of dust events were also identified, with the most and least frequencies in July and December, respectively. In terms of long-term frequency of dust events, our observational analyses show an overall rising trend of the frequency of Iran's dust events in recent years, predominantly attributed to increasingly frequent dust outbreaks in Iraq due to human intervention.